Working!

Adding extract_from functionality + unit tests

.github/workflows/aarch64.yml

@@ -1,4 +1,4 @@
-name: Ubuntu ppc64le (GCC 11)
+name: Ubuntu aarch64 (GCC 13)
 
 on:
   push:

.github/workflows/ubuntu24-cxx20-noexcept.yml

@@ -0,0 +1,22 @@
+name: Ubuntu 24.04 CI (CXX 20, noexcept)
+
+on: [push, pull_request]
+jobs:
+  ubuntu-build:
+    if: >-
+      ! contains(toJSON(github.event.commits.*.message), '[skip ci]') &&
+      ! contains(toJSON(github.event.commits.*.message), '[skip github]')
+    runs-on: ubuntu-24.04
+    strategy:
+      matrix:
+        cxx: [g++-13, clang++-16]
+    steps:
+      - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29 # v4.1.6
+      - name: Prepare
+        run: cmake -DSIMDJSON_CXX_STANDARD=20 -DSIMDJSON_EXCEPTIONS=OFF -DSIMDJSON_DEVELOPER_MODE=ON  -B build
+        env:
+          CXX: ${{matrix.cxx}}
+      - name: Build
+        run: cmake --build build -j=2
+      - name: Test
+        run: ctest --output-on-failure --test-dir build

.github/workflows/ubuntu24-noexcept.yml

@@ -31,4 +31,4 @@ jobs:
           echo -e '#include <simdjson.h>\nint main(int argc,char**argv) {simdjson::dom::parser parser;simdjson::dom::element tweets = parser.load(argv[1]); }' > tmp.cpp && c++ -Idestination/include -Ldestination/lib -std=c++17 -Wl,-rpath,destination/lib -o linkandrun tmp.cpp -lsimdjson && ./linkandrun jsonexamples/twitter.json &&
           mkdir testfindpackage &&
           cd testfindpackage &&
-          echo -e 'cmake_minimum_required(VERSION 3.1)\nproject(simdjsontester)\nset(CMAKE_CXX_STANDARD 17)\nfind_package(simdjson REQUIRED)'> CMakeLists.txt && mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../destination .. &&  cmake --build .
+          echo -e 'cmake_minimum_required(VERSION 3.14)\nproject(simdjsontester)\nset(CMAKE_CXX_STANDARD 17)\nfind_package(simdjson REQUIRED)'> CMakeLists.txt && mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../destination .. &&  cmake --build .

.github/workflows/ubuntu24-nothread.yml

@@ -31,4 +31,4 @@ jobs:
           echo -e '#include <simdjson.h>\nint main(int argc,char**argv) {simdjson::dom::parser parser;simdjson::dom::element tweets = parser.load(argv[1]); }' > tmp.cpp && c++ -Idestination/include -Ldestination/lib -std=c++17 -Wl,-rpath,destination/lib -o linkandrun tmp.cpp -lsimdjson && ./linkandrun jsonexamples/twitter.json &&
           mkdir testfindpackage &&
           cd testfindpackage &&
-          echo -e 'cmake_minimum_required(VERSION 3.1)\nproject(simdjsontester)\nset(CMAKE_CXX_STANDARD 17)\nfind_package(simdjson REQUIRED)'> CMakeLists.txt && mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../destination .. &&  cmake --build .
+          echo -e 'cmake_minimum_required(VERSION 3.14)\nproject(simdjsontester)\nset(CMAKE_CXX_STANDARD 17)\nfind_package(simdjson REQUIRED)'> CMakeLists.txt && mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX:PATH=../destination .. &&  cmake --build .

CMakeLists.txt

@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 3.14)
 project(
     simdjson
     # The version number is modified by tools/release.py
-    VERSION 4.0.0
+    VERSION 4.0.7
     DESCRIPTION "Parsing gigabytes of JSON per second"
     HOMEPAGE_URL "https://simdjson.org/"
     LANGUAGES CXX C

Doxyfile

@@ -38,7 +38,7 @@ PROJECT_NAME           = simdjson
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = "4.0.0"
+PROJECT_NUMBER         = "4.0.7"
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a

README.md

@@ -62,6 +62,7 @@ Real-world usage
 - [WasmEdge](https://wasmedge.org)
 - [RonDB](https://github.com/logicalclocks/rondb)
 - [GreptimeDB](https://github.com/GreptimeTeam/greptimedb)
+- [mamba](https://github.com/mamba-org/mamba)
 
 
 If you are planning to use simdjson in a product, please work from one of our releases.
@@ -117,6 +118,7 @@ Godbolt
 -------------
 
 Some users may want to browse code along with the compiled assembly. You want to check out the following lists of examples:
+* [C++26 reflection example](https://godbolt.org/z/K3Px64TqK)
 * [simdjson examples with errors handled through exceptions](https://godbolt.org/z/7G5qE4sr9)
 * [simdjson examples with errors without exceptions](https://godbolt.org/z/e9dWb9E4v)
 

benchmark/distinct_user_id/yyjson.h

@@ -44,7 +44,10 @@ struct yyjson_base {
 
 struct yyjson : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<uint64_t> &result) {
-    return yyjson_base::run(yyjson_read(json.data(), json.size(), 0), result);
+    yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(distinct_user_id, yyjson)->UseManualTime();
@@ -52,11 +55,15 @@ BENCHMARK_TEMPLATE(distinct_user_id, yyjson)->UseManualTime();
 #if SIMDJSON_COMPETITION_ONDEMAND_INSITU
 struct yyjson_insitu : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<uint64_t> &result) {
-    return yyjson_base::run(yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0), result);
+    yyjson_doc *doc = yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(distinct_user_id, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
+
 } // namespace distinct_user_id
 
 #endif // SIMDJSON_COMPETITION_YYJSON

benchmark/find_tweet/yyjson.h

@@ -36,18 +36,26 @@ struct yyjson_base {
 
 struct yyjson : yyjson_base {
   bool run(simdjson::padded_string &json, uint64_t find_id, std::string_view &result) {
-    return yyjson_base::run(yyjson_read(json.data(), json.size(), 0), find_id, result);
+    yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
+    bool b = yyjson_base::run(doc, find_id, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(find_tweet, yyjson)->UseManualTime();
+
 #if SIMDJSON_COMPETITION_ONDEMAND_INSITU
 struct yyjson_insitu : yyjson_base {
   bool run(simdjson::padded_string &json, uint64_t find_id, std::string_view &result) {
-    return yyjson_base::run(yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0), find_id, result);
+    yyjson_doc *doc = yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
+    bool b = yyjson_base::run(doc, find_id, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(find_tweet, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
+
 } // namespace find_tweet
 
 #endif // SIMDJSON_COMPETITION_YYJSON

benchmark/json2msgpack/yyjson.h

@@ -100,6 +100,7 @@ struct yyjson : yyjson2msgpack {
            std::string_view &result) {
     yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
     result = to_msgpack(doc, reinterpret_cast<uint8_t*>(buffer));
+    yyjson_doc_free(doc);
     return true;
   }
 };
@@ -113,6 +114,7 @@ struct yyjson_insitu : yyjson2msgpack {
     yyjson_doc *doc =
         yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
     result = to_msgpack(doc, reinterpret_cast<uint8_t*>(buffer));
+    yyjson_doc_free(doc);
     return true;
   }
 };
@@ -120,4 +122,4 @@ BENCHMARK_TEMPLATE(json2msgpack, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
 } // namespace json2msgpack
 
-#endif // SIMDJSON_COMPETITION_YYJSON
+#endif // SIMDJSON_COMPETITION_YYJSON

benchmark/kostya/yyjson.h

@@ -49,18 +49,26 @@ struct yyjson_base {
 
 struct yyjson : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<point> &result) {
-    return yyjson_base::run(yyjson_read(json.data(), json.size(), 0), result);
+    yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(kostya, yyjson)->UseManualTime();
+
 #if SIMDJSON_COMPETITION_ONDEMAND_INSITU
 struct yyjson_insitu : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<point> &result) {
-    return yyjson_base::run(yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0), result);
+    yyjson_doc *doc = yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(kostya, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
+
 } // namespace kostya
 
 #endif // SIMDJSON_COMPETITION_YYJSON

benchmark/large_random/yyjson.h

@@ -47,18 +47,26 @@ struct yyjson_base {
 
 struct yyjson : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<point> &result) {
-    return yyjson_base::run(yyjson_read(json.data(), json.size(), 0), result);
+    yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(large_random, yyjson)->UseManualTime();
+
 #if SIMDJSON_COMPETITION_ONDEMAND_INSITU
 struct yyjson_insitu : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<point> &result) {
-    return yyjson_base::run(yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0), result);
+    yyjson_doc *doc = yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(large_random, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
+
 } // namespace large_random
 
 #endif // SIMDJSON_COMPETITION_YYJSON

benchmark/partial_tweets/yyjson.h

@@ -62,19 +62,26 @@ struct yyjson_base {
 
 struct yyjson : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<tweet<std::string_view>> &result) {
-    return yyjson_base::run(yyjson_read(json.data(), json.size(), 0), result);
+    yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(partial_tweets, yyjson)->UseManualTime();
+
 #if SIMDJSON_COMPETITION_ONDEMAND_INSITU
 struct yyjson_insitu : yyjson_base {
   bool run(simdjson::padded_string &json, std::vector<tweet<std::string_view>> &result) {
-    return yyjson_base::run(yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0), result);
+    yyjson_doc *doc = yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
+    bool b = yyjson_base::run(doc, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(partial_tweets, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
+
 } // namespace partial_tweets
 
 #endif // SIMDJSON_COMPETITION_YYJSON
-

benchmark/static_reflect/CMakeLists.txt

@@ -6,38 +6,42 @@ CPMAddPackage(
   EXCLUDE_FROM_ALL YES
 )
 
+option(SIMDJSON_USE_RUST "Build the static_reflect benchmark" OFF)
 
-
-if(NOT WIN32)
-# We want the check whether Rust is available before trying to build a crate.
-CPMAddPackage(
-  NAME corrosion
-  GITHUB_REPOSITORY corrosion-rs/corrosion
-  VERSION 0.4.4
-  DOWNLOAD_ONLY ON
-  OPTIONS "Rust_FIND_QUIETLY OFF"
-)
-include("${corrosion_SOURCE_DIR}/cmake/FindRust.cmake")
-endif()
-
-if(RUST_FOUND)
-  message(STATUS "Rust found: " ${Rust_VERSION} )
-  add_subdirectory("${corrosion_SOURCE_DIR}" "${PROJECT_BINARY_DIR}/_deps/corrosion" EXCLUDE_FROM_ALL)
-  # Important: we want to build in release mode!
-  corrosion_import_crate(MANIFEST_PATH "serde-benchmark/Cargo.toml" NO_LINKER_OVERRIDE PROFILE release)
-else()
-  message(STATUS "Rust/Cargo is unavailable." )
-  message(STATUS "We will not benchmark serde-benchmark." )
-  if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
-    message(STATUS "Under macOS, you may be able to install rust with")
-    message(STATUS "curl https://sh.rustup.rs -sSf | sh")
-  elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
-    message(STATUS "Under Linux, you may be able to install rust with a command such as")
-    message(STATUS "apt-get install cargo" )
-    message(STATUS "or" )
-    message(STATUS "curl https://sh.rustup.rs -sSf | sh")
+if(SIMDJSON_USER_RUST)
+  if(NOT WIN32)
+  # We want the check whether Rust is available before trying to build a crate.
+  CPMAddPackage(
+    NAME corrosion
+    GITHUB_REPOSITORY corrosion-rs/corrosion
+    VERSION 0.4.4
+    DOWNLOAD_ONLY ON
+    OPTIONS "Rust_FIND_QUIETLY OFF"
+  )
+  include("${corrosion_SOURCE_DIR}/cmake/FindRust.cmake")
   endif()
-endif()
+
+  if(RUST_FOUND)
+    message(STATUS "Rust found: " ${Rust_VERSION} )
+    add_subdirectory("${corrosion_SOURCE_DIR}" "${PROJECT_BINARY_DIR}/_deps/corrosion" EXCLUDE_FROM_ALL)
+    # Important: we want to build in release mode!
+    corrosion_import_crate(MANIFEST_PATH "serde-benchmark/Cargo.toml" NO_LINKER_OVERRIDE PROFILE release)
+  else()
+    message(STATUS "Rust/Cargo is unavailable." )
+    message(STATUS "We will not benchmark serde-benchmark." )
+    if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+      message(STATUS "Under macOS, you may be able to install rust with")
+      message(STATUS "curl https://sh.rustup.rs -sSf | sh")
+    elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+      message(STATUS "Under Linux, you may be able to install rust with a command such as")
+      message(STATUS "apt-get install cargo" )
+      message(STATUS "or" )
+      message(STATUS "curl https://sh.rustup.rs -sSf | sh")
+    endif()
+  endif()
+else(SIMDJSON_USER_RUST)
+  message(STATUS "We will not benchmark serde-benchmark." )
+endif(SIMDJSON_USER_RUST)
 
 # Add the benchmark executable targets
 add_subdirectory(twitter_benchmark)

benchmark/top_tweet/yyjson.h

@@ -51,18 +51,26 @@ struct yyjson_base {
 
 struct yyjson : yyjson_base {
   bool run(simdjson::padded_string &json, int64_t max_retweet_count, top_tweet_result<StringType> &result) {
-    return yyjson_base::run(yyjson_read(json.data(), json.size(), 0), max_retweet_count, result);
+    yyjson_doc *doc = yyjson_read(json.data(), json.size(), 0);
+    bool b = yyjson_base::run(doc, max_retweet_count, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(top_tweet, yyjson)->UseManualTime();
+
 #if SIMDJSON_COMPETITION_ONDEMAND_INSITU
 struct yyjson_insitu : yyjson_base {
   bool run(simdjson::padded_string &json, int64_t max_retweet_count, top_tweet_result<StringType> &result) {
-    return yyjson_base::run(yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0), max_retweet_count, result);
+    yyjson_doc *doc = yyjson_read_opts(json.data(), json.size(), YYJSON_READ_INSITU, 0, 0);
+    bool b = yyjson_base::run(doc, max_retweet_count, result);
+    yyjson_doc_free(doc);
+    return b;
   }
 };
 BENCHMARK_TEMPLATE(top_tweet, yyjson_insitu)->UseManualTime();
 #endif // SIMDJSON_COMPETITION_ONDEMAND_INSITU
+
 } // namespace top_tweet
 
 #endif // SIMDJSON_COMPETITION_YYJSON

cmake/developer-options.cmake

@@ -4,7 +4,7 @@
 add_library(simdjson-internal-flags INTERFACE)
 if(NOT DEFINED CMAKE_POSITION_INDEPENDENT_CODE)
   # We default to ON for all targets, so that we can use the library in shared libraries.
-  set_target_properties(simdjson-internal-flags PROPERTIES POSITION_INDEPENDENT_CODE ON)
+  set_target_properties(simdjson-internal-flags PROPERTIES INTERFACE_POSITION_INDEPENDENT_CODE ON)
 endif(NOT DEFINED CMAKE_POSITION_INDEPENDENT_CODE)
 
 option(SIMDJSON_CHECK_EOF "Check for the end of the input buffer. The setting is unnecessary since we require padding of the inputs. You should expect tests to fail with this option turned on." OFF)
@@ -174,6 +174,10 @@ else()
       -Werror -Wall -Wextra -Weffc++ -Wsign-compare -Wshadow -Wwrite-strings
       -Wpointer-arith -Winit-self -Wconversion -Wno-sign-conversion
   )
+  if(CMAKE_CXX_STANDARD VERSION_GREATER_EQUAL 20)
+    target_compile_options(simdjson-internal-flags INTERFACE -Wctad-maybe-unsupported)
+  endif()
+
 endif()
 
 option(SIMDJSON_GLIBCXX_ASSERTIONS "Set _GLIBCXX_ASSERTIONS" OFF)

doc/basics.md

@@ -452,7 +452,7 @@ support for users who avoid exceptions. See [the simdjson error handling documen
 * **Field Access:** To get the value of the "foo" field in an object, use `object["foo"]`. This will
   scan through the object looking for the field with the matching string, doing a character-by-character
   comparison. It may generate the error `simdjson::NO_SUCH_FIELD` if there is no such key in the object, it may throw an exception (see [Error handling](#error-handling)). For efficiency reason, you should avoid looking up the same field repeatedly: e.g., do
-  not do `object["foo"]` followed by `object["foo"]` with the same `object` instance. Generally, you should not mix and match iterating through an object (`for(auto field : object) {...}`) and key accesses (`object["foo"]`): if you need to iterate through an object after a key access, you need to call `reset()` on the object. Whenever you call `reset()`, you need to keep in mind that though you can iterate over the array repeatedly, values should be consumedonly once (e.g., repeatedly calling `unescaped_key()` on the same  key is forbidden). Keep in mind that On-Demand does not buffer or save the result of the parsing: if you repeatedly access `object["foo"]`, then it must repeatedly seek the key and parse the content. The library does not provide a distinct function to check if a key is present, instead we recommend you attempt to access the key: e.g., by doing `ondemand::value val{}; if (!object["foo"].get(val)) {...}`, you have that `val` contains the requested value inside the if clause.  It is your responsibility as a user to temporarily keep a reference to the value (`auto v = object["foo"]`), or to consume the content and store it in your own data structures. If you consume an
+  not do `object["foo"]` followed by `object["foo"]` with the same `object` instance. Generally, you should not mix and match iterating through an object (`for(auto field : object) {...}`) and key accesses (`object["foo"]`): if you need to iterate through an object after a key access, you need to call `reset()` on the object. Whenever you call `reset()`, you need to keep in mind that though you can iterate over the array repeatedly, values should be consumed only once (e.g., repeatedly calling `unescaped_key()` on the same  key is forbidden). Keep in mind that On-Demand does not buffer or save the result of the parsing: if you repeatedly access `object["foo"]`, then it must repeatedly seek the key and parse the content. The library does not provide a distinct function to check if a key is present, instead we recommend you attempt to access the key: e.g., by doing `ondemand::value val{}; if (!object["foo"].get(val)) {...}`, you have that `val` contains the requested value inside the if clause.  It is your responsibility as a user to temporarily keep a reference to the value (`auto v = object["foo"]`), or to consume the content and store it in your own data structures. If you consume an
   object twice: `std::string_view(object["foo"]` followed by `std::string_view(object["foo"]` then your code
   is in error. Furthermore, you can only consume one field at a time, on the same object. The
   value instance you get from  `content["bids"]` becomes invalid when you call `content["asks"]`.
@@ -1395,12 +1395,48 @@ Car c = doc.get<Car>();
 
 We try to automate the parsing of any given structure or class
 by looking at its non-static public members. At compile-time,
-the library looks at a simple structre like `Car` and
+the library looks at a simple structure like `Car` and
 maps it to parsing code. We call the default constructor,
 and then assign values to the public members.
 
 
-#### Special cases 
+If a key is missing in the JSON document, an error is generated (`NO_SUCH_FIELD`),
+except if the attribute is of a type like `std::optional` (`simdjson::concepts::optional_type`).
+
+
+Sometimes you might want to only extract some attributes from the JSON. You can
+achieve this result with the `extract_into` method supported by both `object` and
+`document` instances. It returns an error code that evaluates to false when there
+is no error.
+
+Consider the following example where you only want to parse the make and the model
+from the JSON:
+
+```cpp
+struct car_type {
+    std::string make;
+    std::string model;
+    uint64_t year;
+    std::vector<double> tire_pressure;
+};
+
+void f() {
+  auto json = R"( {
+         "make": "Toyota",
+         "model": "Camry",
+         "year": 2024,
+         "tire_pressure": [ 40.1, 39.9 ]
+       } )"_padded;
+  ondemand::parser parser;
+  ondemand::document doc = parser.iterate(json);
+  Car car{};
+  auto error = doc.extract_into<"make","model">(car);
+  if(error) { /** error handling */ }
+  // only car.make and car.
+}
+```
+
+#### Special cases
 
 However, there are instances where the construction cannot
 be easily automated. Let us consider a class without any
@@ -1450,13 +1486,13 @@ struct complicated_weather_data {
 };
 ```
 
-The code might as simple as the following.
+The code might be as simple as the following.
 
 ```cpp
 auto padded = R"({"time":["2023-03-15T12:00:00Z"],"temperature":[42]})"_padded;
 simdjson::ondemand::parser parser;
 simdjson::ondemand::document doc = parser.iterate(padded);
-complicated_weather_data p = doc.get<>(complicated_weather_data);
+complicated_weather_data p = doc.get<complicated_weather_data>();
 ```
 
 Thus you can combine C++26 static reflection with custom deserialization
@@ -1477,6 +1513,12 @@ type without a document instance like so:
 Car car = simdjson::from(json);
 ```
 
+You can also use the `simdjson::from` syntax without exceptions, like so:
+```cpp
+Car car;
+simdjson::error_code err = simdjson::from(json_car).get(car);
+```
+
 You can also use the `simdjson::from` syntax to iterate over an array.
 
 ```cpp
@@ -2765,15 +2807,16 @@ a parameter a reference to a `std::string`.
   ondemand::parser parser;
   ondemand::document doc = parser.iterate(json);
   std::string name;
-  doc["name"].get_string(name);
+  auto error = doc["name"].get_string(name);
+  if(error) { /* handle error */ }
 ```
 
 The same routine can be written without exceptions handling:
 
 ```C++
   std::string name;
-  auto err = doc["name"].get_string(name);
-  if (err) { /* handle error */ }
+  auto error = doc["name"].get_string(name);
+  if (error) { /* handle error */ }
 ```
 
 The `std::string` instance, once created, is independent. Unlike our `std::string_view` instances,

doc/builder.md

@@ -34,14 +34,15 @@ It has the following methods to add content to the string:
 - `append_null()`: Appends the string "null" to the JSON buffer.
 - `clear()`: Clears the contents of the JSON buffer, resetting the position to 0 while retaining the allocated capacity.
 - `escape_and_append(std::string_view input)`: Appends a string view to the JSON buffer after escaping special characters (e.g., quotes, backslashes) as required by JSON.
-- `escape_and_append_with_quotes(std::string_view input)` Appends a string view surrounded by double quotes (e.g., "input") to the JSON buffer after escaping special characters.
-Parameters:
+- `escape_and_append_with_quotes(std::string_view input)` Appends a string view surrounded by double quotes (e.g., "input") to the JSON buffer after escaping special characters. For constant strings, you may also do `escape_and_append_with_quotes<"mystring">()`.
 - `escape_and_append_with_quotes(char input)`: Appends a single character surrounded by double quotes (e.g., "c") to the JSON buffer after escaping it if necessary.
 - `append_raw(const char *c)`: Appends a null-terminated C string directly to the JSON buffer without escaping.
 - `append_raw(std::string_view input)`: Appends a string view directly to the JSON buffer without escaping.
 - `append_raw(const char *str, size_t len)`: Appends a specified number of characters from a C string directly to the JSON
+- `append_key_value(key,value)`: Appends a key and a value (`"json":somevalue`)
+- `append_key_value<"mykey">(value)`: Appends a key and a value (`"json":somevalue`), useful when the key is a compile-time constant (C++20).
 
-After writting the content, if you have reasons to believe that the content might violate UTF-8 conventions, you can check it as follows:
+After writing the content, if you have reasons to believe that the content might violate UTF-8 conventions, you can check it as follows:
 
 - `validate_unicode()`: Checks if the content in the JSON buffer is valid UTF-8. Returns: true if the content is valid UTF-8, false otherwise.
 
@@ -52,7 +53,7 @@ Once you are satisfied, you can recover the string as follows:
 
 - `operator std::string()`: Converts the JSON buffer to an std::string. (Might throw if an error occurred.)
 - `operator std::string_view()`: Converts the JSON buffer to an std::string_view.  (Might throw if an error occurred.)
-- `view()`: Returns a view of the written JSON buffer as a `simdjson_result<std::string_view>`.
+- `view()`: Returns a view of the written JSON buffer as a `simdjson_result<std::string_view>` (C++20).
 
 The later method (`view()`) is recommended.  For performance reasons, we expect you to explicitly call `validate_unicode()` as needed (e.g., prior to calling `view()`).
 
@@ -131,20 +132,20 @@ In all cases, the `std::string_view` instance depends the corresponding `string_
 
 
 
-If you have C++20, you can simplify the code, as the `std::vector<double>` is automatically
-supported.
+If you have C++20, you can simplify the code, as the `std::vector<double>` is automatically supported. Further, we can pass the keys (which are compile-time
+constant) as template parameter (for improved performance).
 
 ```cpp
     Car c = {"Toyota", "Corolla", 2017, {30.0,30.2,30.513,30.79}};
     simdjson::builder::string_builder sb;
     sb.start_object();
-    sb.append_key_value("make", c.make);
+    sb.append_key_value<"make">(c.make);
     sb.append_comma();
-    sb.append_key_value("model", c.model);
+    sb.append_key_value<"model">(c.model);
     sb.append_comma();
-    sb.append_key_value("year", c.year);
+    sb.append_key_value<"year">(c.year);
     sb.append_comma();
-    sb.append_key_value("tire_pressure", c.tire_pressure);
+    sb.append_key_value<"tire_pressure">(c.tire_pressure);
     sb.end_object();
     std::string_view p = sb.view();
 ```
@@ -175,9 +176,52 @@ std::vector<std::vector<double>> c = {{1.0, 2.0}, {3.0, 4.0}};
 std::string json = simdjson::to_json(c);
 ```
 
+We also have an overload for when you want to reuse the same `std::string` instance:
+
+
+```cpp
+std::vector<std::vector<double>> c = {{1.0, 2.0}, {3.0, 4.0}};
+std::string json;
+auto error = simdjson::to_json(c, json);
+if(error) { /* there was an error */ }
+```
+
+
 We do recommend that you create and reuse the `string_builder` instance for performance
 reasons.
 
+You can also add custom serialization functions using a `tag_invoke` function.
+For example, the following
+function will allow you to serialize instances of the type `Car`.
+
+```cpp
+#include <simdjson>
+
+struct Car {
+  std::string make;
+  std::string model;
+  int64_t year;
+  std::vector<float> tire_pressure;
+};
+
+namespace simdjson {
+
+template <typename builder_type>
+void tag_invoke(serialize_tag, builder_type &builder, const Car& car) {
+  builder.start_object();
+  builder.append_key_value("make", car.make);
+  builder.append_comma();
+  builder.append_key_value("model", car.model);
+  builder.append_comma();
+  builder.append_key_value("year", car.year);
+  builder.append_comma();
+  builder.append_key_value("tire_pressure", car.tire_pressure);
+  builder.end_object();
+}
+
+} // namespace simdjson
+```
+
 C++26 static reflection
 ------------------------
 
@@ -239,7 +283,38 @@ with the `simdjson::to_json` template function.
 If you know the output size, in bytes, of your JSON string, you may
 pass it as a second parameter (e.g., `simdjson::to_json(c, 31123)`).
 
+Sometimes you may want to reuse the same `std::string` instance. We
+have an overload for this purpose:
 
+```cpp
+Car c = {"Toyota", "Corolla", 2017, {30.0,30.2,30.513,30.79}};
+std::string s;
+auto error = simdjson::to_json(c, s);
+if(error) { /* there was an error */ }
+```
+
+You can then also add a third parameter for the expected output size in bytes.
+
+### Extracting just some fields
+In some instances, your class might have many fields that you do not want to serialize.
+You can achieve this result with the `simdjson::extract_from` template. In the following
+example, we serialize only the `year` and `price` fields on the `Car` instance.
+```cpp
+struct Car {
+    std::string make;
+    std::string model;
+    int year;
+    double price;
+    bool electric;
+};
+Car car{"Ford", "F-150", 2024, 55000.0, false};
+// Extract year and price
+std::string json_result = simdjson::extract_from<"year", "price">(car);
+// Alternatively:
+// std::string json_result;
+// auto error =  extract_from<"year", "price">(car).get(json_result);
+// if(error) { /* error handling */ }
+```
 
 ### Without `string_buffer` instance but with explicit error handling
 
@@ -248,9 +323,44 @@ pattern:
 
 ```cpp
   std::string json;
-  if(simdjson::to(c).get(json)) {
+  if(simdjson::to_json(c).get(json)) {
     // there was an error
   } else {
     // json contain the serialized JSON
   }
+```
+
+### Customization
+
+If you want to serialize a value in a custome way, you can do it with a
+`tag_invoke` specialization like the following example which will map
+the year attribute to a string.
+
+
+```cpp
+#include <simdjson>
+
+struct Car {
+  std::string make;
+  std::string model;
+  int64_t year;
+  std::vector<float> tire_pressure;
+};
+
+namespace simdjson {
+
+template <typename builder_type>
+void tag_invoke(serialize_tag, builder_type &builder, const Car& car) {
+  builder.start_object();
+  builder.append_key_value("make", car.make);
+  builder.append_comma();
+  builder.append_key_value("model", car.model);
+  builder.append_comma();
+  builder.append_key_value("year", std::to_string(car.year));
+  builder.append_comma();
+  builder.append_key_value("tire_pressure", car.tire_pressure);
+  builder.end_object();
+}
+
+} // namespace simdjson
 ```

doc/dom.md

@@ -129,7 +129,7 @@ Once you have an element, you can navigate it with idiomatic C++ iterators, oper
   The strings contain unescaped valid UTF-8 strings: no unmatched surrogate is allowed.
   Internally, numbers are stored as either 64-bit integers or 64-bit floating-point numbers.
   Thus it is possible to get the full 64-bit integer range (either signed or  unsigned).
-  By default, the string `-0` is parsed as the integer 0 as in Pytho or C++. If you set the macro
+  By default, the string `-0` is parsed as the integer 0 as in Python or C++. If you set the macro
   `SIMDJSON_MINUS_ZERO_AS_FLOAT` to `1` when building simdjson, you can get that `-0` is mapped to `-0.0`
   as in JavaScript. You can get the desired effect by building simdjson with cmake setting the
   `SIMDJSON_MINUS_ZERO_AS_FLOAT` to on: `cmake -B build -D SIMDJSON_MINUS_ZERO_AS_FLOAT=ON`.

doc/performance.md

@@ -253,7 +253,7 @@ long page_size() {
 // page boundary.
 bool need_allocation(const char *buf, size_t len) {
   return ((reinterpret_cast<uintptr_t>(buf + len - 1) % page_size())
-    + simdjson::SIMDJSON_PADDING > static_cast<uintptr_t>(page_size()));
+    + simdjson::SIMDJSON_PADDING >= static_cast<uintptr_t>(page_size()));
 }
 
 simdjson::padded_string_view

include/simdjson/arm64/stringparsing_defs.h

@@ -17,7 +17,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 32;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return ((bs_bits - 1) & quote_bits) != 0; }
   simdjson_inline bool has_backslash() { return bs_bits != 0; }

include/simdjson/concepts.h

@@ -122,11 +122,46 @@ concept optional_type = requires(std::remove_cvref_t<T> obj) {
     } -> std::convertible_to<typename std::remove_cvref_t<T>::value_type>;
   };
   { static_cast<bool>(obj) } -> std::same_as<bool>; // convertible to bool
+  { obj.reset() } noexcept -> std::same_as<void>;
 };
 
 
 
+// Types we serialize as JSON strings (not as containers)
+template <typename T>
+concept string_like =
+  std::is_same_v<std::remove_cvref_t<T>, std::string> ||
+  std::is_same_v<std::remove_cvref_t<T>, std::string_view> ||
+  std::is_same_v<std::remove_cvref_t<T>, const char*> ||
+  std::is_same_v<std::remove_cvref_t<T>, char*>;
+
+// Concept that checks if a type is a container but not a string (because
+// strings handling must be handled differently)
+// Now uses iterator-based approach for broader container support
+template <typename T>
+concept container_but_not_string =
+  std::ranges::input_range<T> && !string_like<T> && !concepts::string_view_keyed_map<T>;
+
+
 } // namespace concepts
+
+
+/**
+ * We use tag_invoke as our customization point mechanism.
+ */
+template <typename Tag, typename... Args>
+concept tag_invocable = requires(Tag tag, Args... args) {
+  tag_invoke(std::forward<Tag>(tag), std::forward<Args>(args)...);
+};
+
+template <typename Tag, typename... Args>
+concept nothrow_tag_invocable =
+    tag_invocable<Tag, Args...> && requires(Tag tag, Args... args) {
+      {
+        tag_invoke(std::forward<Tag>(tag), std::forward<Args>(args)...)
+      } noexcept;
+    };
+
 } // namespace simdjson
 #endif // SIMDJSON_SUPPORTS_CONCEPTS
 #endif // SIMDJSON_CONCEPTS_H

include/simdjson/constevalutil.h

@@ -5,9 +5,9 @@
 #include <string_view>
 #include <array>
 
-#if SIMDJSON_CONSTEVAL
 namespace simdjson {
 namespace constevalutil {
+#if SIMDJSON_CONSTEVAL
 
 constexpr static std::array<uint8_t, 256> json_quotable_character = {
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
@@ -47,7 +47,30 @@ consteval std::string consteval_to_quoted_escaped(std::string_view input) {
   out.push_back('"');
   return out;
 }
+#endif  // SIMDJSON_CONSTEVAL
+
+
+#if SIMDJSON_SUPPORTS_CONCEPTS
+template <std::size_t N>
+struct fixed_string {
+    constexpr fixed_string() : data{} {}  // Default constructor for buffers
+    constexpr fixed_string(const char (&str)[N])  {
+        for (std::size_t i = 0; i < N; ++i) {
+            data[i] = str[i];
+        }
+    }
+    char data[N];
+    constexpr std::string_view view() const { return {data, N - 1}; }
+};
+template <std::size_t N>
+fixed_string(const char (&)[N]) -> fixed_string<N>;
+
+template <fixed_string str>
+struct string_constant {
+    static constexpr std::string_view value = str.view();
+};
+#endif // SIMDJSON_SUPPORTS_CONCEPTS
+
 } // namespace constevalutil
 } // namespace simdjson
-#endif  // SIMDJSON_CONSTEVAL
 #endif // SIMDJSON_CONSTEVALUTIL_H

include/simdjson/convert-inl.h

@@ -58,6 +58,12 @@ inline simdjson_result<T> auto_parser<parser_type>::result() noexcept(is_nothrow
   return m_doc.get<T>();
 }
 
+template <typename parser_type>
+template <typename T>
+simdjson_warn_unused simdjson_inline error_code auto_parser<parser_type>::get(T &value) && noexcept(is_nothrow_gettable<T>) {
+  return result<T>().get(value);
+}
+
 template <typename parser_type>
 inline simdjson_result<ondemand::array> auto_parser<parser_type>::array() noexcept {
   return result<ondemand::array>();
@@ -73,12 +79,7 @@ inline simdjson_result<ondemand::number> auto_parser<parser_type>::number() noex
   return result<ondemand::number>();
 }
 
-template <typename parser_type>
-template <typename T>
-inline auto_parser<parser_type>::operator simdjson_result<T>() noexcept(is_nothrow_gettable<T>) {
-  return result<T>();
-}
-
+#if SIMDJSON_EXCEPTIONS
 template <typename parser_type>
 template <typename T>
 inline auto_parser<parser_type>::operator T() noexcept(false) {
@@ -87,6 +88,7 @@ inline auto_parser<parser_type>::operator T() noexcept(false) {
   }
   return m_doc.get<T>();
 }
+#endif // SIMDJSON_EXCEPTIONS
 
 template <typename parser_type>
 template <typename T>
@@ -109,13 +111,23 @@ inline T to_adaptor<T>::operator()(simdjson_result<ondemand::value> &val) const
 
 template <typename T>
 inline auto to_adaptor<T>::operator()(padded_string_view const str) const noexcept {
-  return auto_parser{str};
+  return auto_parser<ondemand::parser *>{str};
 }
 
 template <typename T>
 inline auto to_adaptor<T>::operator()(ondemand::parser &parser, padded_string_view const str) const noexcept {
   return auto_parser<ondemand::parser *>{parser, str};
 }
+
+template <typename T>
+inline auto to_adaptor<T>::operator()(std::string str) const noexcept {
+  return auto_parser<ondemand::parser *>{pad_with_reserve(str)};
+}
+
+template <typename T>
+inline auto to_adaptor<T>::operator()(ondemand::parser &parser, std::string str) const noexcept {
+  return auto_parser<ondemand::parser *>{parser, pad_with_reserve(str)};
+}
 } // namespace internal
 } // namespace convert
 } // namespace simdjson

include/simdjson/convert.h

@@ -46,16 +46,19 @@ public:
 
 	template <typename T>
 	simdjson_warn_unused simdjson_inline simdjson_result<T> result() noexcept(is_nothrow_gettable<T>);
+	template <typename T>
+	simdjson_warn_unused simdjson_inline error_code get(T &value) && noexcept(is_nothrow_gettable<T>);
+
 
 	simdjson_warn_unused simdjson_inline simdjson_result<ondemand::array> array() noexcept;
 	simdjson_warn_unused simdjson_inline simdjson_result<ondemand::object> object() noexcept;
 	simdjson_warn_unused simdjson_inline simdjson_result<ondemand::number> number() noexcept;
 
-	template <typename T>
-	simdjson_warn_unused simdjson_inline explicit(false) operator simdjson_result<T>() noexcept(is_nothrow_gettable<T>);
 
+#if SIMDJSON_EXCEPTIONS
 	template <typename T>
 	simdjson_warn_unused simdjson_inline explicit(false) operator T() noexcept(false);
+#endif // SIMDJSON_EXCEPTIONS
 
 	template <typename T>
 	simdjson_warn_unused simdjson_inline std::optional<T> optional() noexcept(is_nothrow_gettable<T>);
@@ -72,7 +75,14 @@ struct to_adaptor {
 	T operator()(simdjson_result<ondemand::value> &val) const noexcept;
 	auto operator()(padded_string_view const str) const noexcept;
 	auto operator()(ondemand::parser &parser, padded_string_view const str) const noexcept;
+	// The std::string is padded with reserve to ensure there is enough space for padding.
+	// Some sanitizers may not like this, so you can use simdjson::pad instead.
+	// simdjson::from(simdjson::pad(str))
+	auto operator()(std::string str) const noexcept;
+	auto operator()(ondemand::parser &parser, std::string str) const noexcept;
 };
+// deduction guide
+auto_parser(padded_string_view const str) -> auto_parser<ondemand::parser*>;
 } // namespace internal
 } // namespace convert
 

include/simdjson/fallback/stringparsing_defs.h

@@ -13,7 +13,7 @@ namespace {
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 1;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return c == '"'; }
   simdjson_inline bool has_backslash() { return c == '\\'; }

include/simdjson/generic/implementation_simdjson_result_base-inl.h

@@ -29,13 +29,13 @@ simdjson_warn_unused simdjson_inline error_code implementation_simdjson_result_b
 }
 
 template<typename T>
-simdjson_inline error_code implementation_simdjson_result_base<T>::error() const noexcept {
+simdjson_warn_unused simdjson_inline error_code implementation_simdjson_result_base<T>::error() const noexcept {
   return this->second;
 }
 
 
 template<typename T>
-simdjson_inline bool implementation_simdjson_result_base<T>::has_value() const noexcept {
+simdjson_warn_unused simdjson_inline bool implementation_simdjson_result_base<T>::has_value() const noexcept {
   return this->error() == SUCCESS;
 }
 

include/simdjson/generic/implementation_simdjson_result_base.h

@@ -67,17 +67,17 @@ struct implementation_simdjson_result_base {
    *
    * @param value The variable to assign the value to. May not be set if there is an error.
    */
-  simdjson_inline error_code get(T &value) && noexcept;
+  simdjson_warn_unused simdjson_inline error_code get(T &value) && noexcept;
 
   /**
    * The error.
    */
-  simdjson_inline error_code error() const noexcept;
+  simdjson_warn_unused simdjson_inline error_code error() const noexcept;
 
   /**
    * Whether there is a value.
    */
-  simdjson_inline bool has_value() const noexcept;
+  simdjson_warn_unused simdjson_inline bool has_value() const noexcept;
 
 #if SIMDJSON_EXCEPTIONS
 

include/simdjson/generic/numberparsing.h

@@ -361,7 +361,7 @@ simdjson_inline bool is_digit(const uint8_t c) {
   return static_cast<uint8_t>(c - '0') <= 9;
 }
 
-simdjson_inline error_code parse_decimal_after_separator(simdjson_unused const uint8_t *const src, const uint8_t *&p, uint64_t &i, int64_t &exponent) {
+simdjson_warn_unused simdjson_inline error_code parse_decimal_after_separator(simdjson_unused const uint8_t *const src, const uint8_t *&p, uint64_t &i, int64_t &exponent) {
   // we continue with the fiction that we have an integer. If the
   // floating point number is representable as x * 10^z for some integer
   // z that fits in 53 bits, then we will be able to convert back the
@@ -389,7 +389,7 @@ simdjson_inline error_code parse_decimal_after_separator(simdjson_unused const u
   return SUCCESS;
 }
 
-simdjson_inline error_code parse_exponent(simdjson_unused const uint8_t *const src, const uint8_t *&p, int64_t &exponent) {
+simdjson_warn_unused simdjson_inline error_code parse_exponent(simdjson_unused const uint8_t *const src, const uint8_t *&p, int64_t &exponent) {
   // Exp Sign: -123.456e[-]78
   bool neg_exp = ('-' == *p);
   if (neg_exp || '+' == *p) { p++; } // Skip + as well
@@ -478,7 +478,7 @@ static error_code slow_float_parsing(simdjson_unused const uint8_t * src, double
 
 /** @private */
 template<typename W>
-simdjson_inline error_code write_float(const uint8_t *const src, bool negative, uint64_t i, const uint8_t * start_digits, size_t digit_count, int64_t exponent, W &writer) {
+simdjson_warn_unused simdjson_inline error_code write_float(const uint8_t *const src, bool negative, uint64_t i, const uint8_t * start_digits, size_t digit_count, int64_t exponent, W &writer) {
   // If we frequently had to deal with long strings of digits,
   // we could extend our code by using a 128-bit integer instead
   // of a 64-bit integer. However, this is uncommon in practice.
@@ -541,13 +541,13 @@ simdjson_inline error_code write_float(const uint8_t *const src, bool negative,
 //
 // Our objective is accurate parsing (ULP of 0) at high speed.
 template<typename W>
-simdjson_inline error_code parse_number(const uint8_t *const src, W &writer);
+simdjson_warn_unused simdjson_inline error_code parse_number(const uint8_t *const src, W &writer);
 
 // for performance analysis, it is sometimes  useful to skip parsing
 #ifdef SIMDJSON_SKIPNUMBERPARSING
 
 template<typename W>
-simdjson_inline error_code parse_number(const uint8_t *const, W &writer) {
+simdjson_warn_unused simdjson_inline error_code parse_number(const uint8_t *const, W &writer) {
   writer.append_s64(0);        // always write zero
   return SUCCESS;              // always succeeds
 }
@@ -573,7 +573,7 @@ simdjson_unused simdjson_inline simdjson_result<number_type> get_number_type(con
 //
 // Our objective is accurate parsing (ULP of 0) at high speed.
 template<typename W>
-simdjson_inline error_code parse_number(const uint8_t *const src, W &writer) {
+simdjson_warn_unused simdjson_inline error_code parse_number(const uint8_t *const src, W &writer) {
   //
   // Check for minus sign
   //

include/simdjson/generic/ondemand/amalgamated.h

@@ -14,6 +14,9 @@
 #include "simdjson/generic/ondemand/raw_json_string.h"
 #include "simdjson/generic/ondemand/parser.h"
 
+// JSON builder - needed for extract_into functionality
+#include "simdjson/generic/ondemand/json_string_builder.h"
+
 // All other declarations
 #include "simdjson/generic/ondemand/array.h"
 #include "simdjson/generic/ondemand/array_iterator.h"
@@ -45,9 +48,11 @@
 #include "simdjson/generic/ondemand/token_iterator-inl.h"
 #include "simdjson/generic/ondemand/value_iterator-inl.h"
 
-// JSON builder, ideally they should not be part of the ondemand directory
-// but it is convenient for now to have them here.
-#include "simdjson/generic/ondemand/json_string_builder.h"
+// JSON builder inline definitions
 #include "simdjson/generic/ondemand/json_string_builder-inl.h"
 #include "simdjson/generic/ondemand/json_builder.h"
 
+// Compile-time JSON parsing (C++26 P2996 reflection)
+#include "simdjson/generic/ondemand/compile_time_json.h"
+#include "simdjson/generic/ondemand/compile_time_json-inl.h"
+

include/simdjson/generic/ondemand/array-inl.h

@@ -85,7 +85,7 @@ simdjson_inline simdjson_result<array_iterator> array::begin() noexcept {
 simdjson_inline simdjson_result<array_iterator> array::end() noexcept {
   return array_iterator(iter);
 }
-simdjson_inline error_code array::consume() noexcept {
+simdjson_warn_unused simdjson_warn_unused simdjson_inline error_code array::consume() noexcept {
   auto error = iter.json_iter().skip_child(iter.depth()-1);
   if(error) { iter.abandon(); }
   return error;

include/simdjson/generic/ondemand/array.h

@@ -141,7 +141,7 @@ public:
    * @returns SUCCESS If the parse succeeded and the out parameter was set to the value.
    */
   template <typename T>
-  simdjson_inline error_code get(T &out)
+  simdjson_warn_unused simdjson_inline error_code get(T &out)
      noexcept(custom_deserializable<T, array> ? nothrow_custom_deserializable<T, array> : true) {
     static_assert(custom_deserializable<T, array>);
     return deserialize(*this, out);
@@ -166,7 +166,7 @@ protected:
   /**
    * Go to the end of the array, no matter where you are right now.
    */
-  simdjson_inline error_code consume() noexcept;
+  simdjson_warn_unused simdjson_inline error_code consume() noexcept;
 
   /**
    * Begin array iteration.
@@ -252,7 +252,7 @@ public:
     return first.get<T>();
   }
   template<typename T>
-  simdjson_inline error_code get(T& out) noexcept {
+  simdjson_warn_unused simdjson_inline error_code get(T& out) noexcept {
     if (error()) { return error(); }
     if constexpr (std::is_same_v<T, SIMDJSON_IMPLEMENTATION::ondemand::array>) {
       out = first;

include/simdjson/generic/ondemand/compile_time_json-inl.h

@@ -0,0 +1,98 @@
+/**
+ * @file compile_time_json-inl.h
+ * @brief Implementation details for compile-time JSON parsing
+ *
+ * This file contains inline implementations and helper utilities for compile-time
+ * JSON parsing. Currently, the main implementation is self-contained in the header.
+ */
+
+#ifndef SIMDJSON_GENERIC_COMPILE_TIME_JSON_INL_H
+
+#ifndef SIMDJSON_CONDITIONAL_INCLUDE
+#define SIMDJSON_GENERIC_COMPILE_TIME_JSON_INL_H
+#include "simdjson/generic/ondemand/compile_time_json.h"
+#endif // SIMDJSON_CONDITIONAL_INCLUDE
+
+#if SIMDJSON_STATIC_REFLECTION
+
+#include <meta>
+#include <array>
+#include <string_view>
+#include <cstdint>
+
+namespace simdjson {
+namespace SIMDJSON_IMPLEMENTATION {
+namespace compile_time {
+
+/**
+ * @brief Optimized constexpr string to integer conversion
+ *
+ * This can be used for more efficient integer parsing in the future.
+ * Currently, we parse all numbers as doubles for simplicity.
+ */
+constexpr int64_t parse_int_fast(std::string_view str) {
+    int64_t result = 0;
+    bool negative = false;
+    std::size_t i = 0;
+
+    if (i < str.size() && str[i] == '-') {
+        negative = true;
+        ++i;
+    }
+
+    while (i < str.size() && str[i] >= '0' && str[i] <= '9') {
+        result = result * 10 + (str[i] - '0');
+        ++i;
+    }
+
+    return negative ? -result : result;
+}
+
+/**
+ * @brief Unescape JSON string at compile-time
+ *
+ * Currently, strings are returned as views into the original JSON.
+ * This function can be used in the future for proper escape handling.
+ */
+template<std::size_t MaxLen = 1024>
+constexpr auto unescape_json_string(std::string_view escaped) {
+    std::array<char, MaxLen> result{};
+    std::size_t out_pos = 0;
+    std::size_t i = 0;
+
+    while (i < escaped.size() && out_pos < MaxLen) {
+        if (escaped[i] == '\\' && i + 1 < escaped.size()) {
+            ++i;
+            switch (escaped[i]) {
+                case '"':  result[out_pos++] = '"'; break;
+                case '\\': result[out_pos++] = '\\'; break;
+                case '/':  result[out_pos++] = '/'; break;
+                case 'b':  result[out_pos++] = '\b'; break;
+                case 'f':  result[out_pos++] = '\f'; break;
+                case 'n':  result[out_pos++] = '\n'; break;
+                case 'r':  result[out_pos++] = '\r'; break;
+                case 't':  result[out_pos++] = '\t'; break;
+                case 'u':
+                    // Unicode escape - would need proper implementation
+                    // For now, skip the escape sequence
+                    i += 4; // Skip 4 hex digits
+                    break;
+                default:
+                    result[out_pos++] = escaped[i];
+            }
+            ++i;
+        } else {
+            result[out_pos++] = escaped[i];
+            ++i;
+        }
+    }
+
+    return std::pair{result, out_pos};
+}
+
+} // namespace compile_time
+} // namespace SIMDJSON_IMPLEMENTATION
+} // namespace simdjson
+
+#endif // SIMDJSON_STATIC_REFLECTION
+#endif // SIMDJSON_GENERIC_COMPILE_TIME_JSON_INL_H

include/simdjson/generic/ondemand/compile_time_json.h

@@ -0,0 +1,464 @@
+/**
+ * @file compile_time_json.h
+ * @brief Compile-time JSON parsing using C++26 reflection with std::meta::substitute()
+ *
+ * Based on the godbolt example: https://godbolt.org/z/Kn5b46T8j
+ * Uses the Outer<Ms...>::Inner + substitute() pattern for recursive type generation.
+ */
+
+#ifndef SIMDJSON_GENERIC_COMPILE_TIME_JSON_H
+
+#ifndef SIMDJSON_CONDITIONAL_INCLUDE
+#define SIMDJSON_GENERIC_COMPILE_TIME_JSON_H
+#include "simdjson/generic/ondemand/base.h"
+#endif // SIMDJSON_CONDITIONAL_INCLUDE
+
+#if SIMDJSON_STATIC_REFLECTION
+
+#include <meta>
+#include <string_view>
+#include <array>
+#include <vector>
+#include <cstdint>
+#include <string>
+#include <algorithm>
+
+namespace simdjson {
+namespace SIMDJSON_IMPLEMENTATION {
+namespace compile_time {
+
+/**
+ * @brief Helper struct for substitute() pattern
+ * The consteval block can use define_aggregate because it's in a template context
+ */
+template <std::meta::info ...Ms>
+struct Outer {
+    struct Inner;
+    consteval {
+        std::meta::define_aggregate(^^Inner, {Ms...});
+    }
+};
+
+/**
+ * @brief Type alias for the generated struct
+ */
+template <std::meta::info ...Ms>
+using Cls = Outer<Ms...>::Inner;
+
+/**
+ * @brief Variable template for constructing instances with values
+ */
+template <typename T, auto ... Vs>
+constexpr auto construct_from = T{Vs...};
+
+// Forward declaration
+consteval std::meta::info parse_json_impl(std::string_view json);
+
+/**
+ * @brief Parse JSON array and return std::meta::info for the generated array
+ */
+consteval std::meta::info parse_json_array_impl(std::string_view json) {
+    auto cursor = json.begin();
+    auto end = json.end();
+
+    auto is_whitespace = [](char c) {
+        return c == ' ' || c == '\n' || c == '\t' || c == '\r';
+    };
+
+    auto skip_whitespace = [&]() -> void {
+        while (cursor != end && is_whitespace(*cursor)) cursor++;
+    };
+
+    auto expect_consume = [&](char c) -> void {
+        skip_whitespace();
+        if (cursor == end || *(cursor++) != c) throw "unexpected character";
+    };
+
+    auto parse_value = [&](std::string &out) -> void {
+        skip_whitespace();
+
+        bool quoted = false;
+        unsigned depth = 0;
+        while (true) {
+            if (cursor == end) throw "unexpected end of stream";
+            if (is_whitespace(*cursor) && !quoted && depth == 0)
+                break;
+
+            if (depth == 0 && (*cursor == ',' || *cursor == ']'))
+                break;
+            out += *(cursor++);
+
+            if (out.back() == '{')
+                ++depth;
+            else if (out.back() == '}')
+                --depth;
+            else if (out.back() == '[')
+                ++depth;
+            else if (out.back() == ']')
+                --depth;
+            else if (out.back() == '"') {
+                if (quoted && depth == 0)
+                    break;
+                quoted = true;
+            }
+        }
+    };
+
+    skip_whitespace();
+    expect_consume('[');
+
+    std::vector<std::meta::info> values = {^^void};
+    std::meta::info element_type = ^^void;
+    bool first = true;
+
+    using std::meta::reflect_constant, std::meta::reflect_constant_string;
+
+    skip_whitespace();
+    if (cursor != end && *cursor == ']') {
+        expect_consume(']');
+        // Empty array - use int as placeholder type since void doesn't work
+        auto array_type = std::meta::substitute(^^std::array, {^^int, reflect_constant(0uz)});
+        values[0] = array_type;
+        return std::meta::substitute(^^construct_from, values);
+    }
+
+    while (cursor != end && *cursor != ']') {
+        std::string value;
+        parse_value(value);
+
+        if (value.empty()) throw "expected value";
+
+        if (value[0] == '"') {
+            if (value.back() != '"') throw "expected end of string";
+            std::string_view contents(&value[1], value.size() - 2);
+
+            if (first) element_type = ^^char const*;
+            values.push_back(reflect_constant_string(contents));
+        } else if (value == "true") {
+            if (first) element_type = ^^bool;
+            values.push_back(reflect_constant(true));
+        } else if (value == "false") {
+            if (first) element_type = ^^bool;
+            values.push_back(reflect_constant(false));
+        } else if (value == "null") {
+            if (first) element_type = ^^std::nullptr_t;
+            values.push_back(reflect_constant(nullptr));
+        } else if ((value[0] >= '0' && value[0] <= '9') || value[0] == '-') {
+            // Try to parse as integer first
+            bool is_int = true;
+            for (char c : value) {
+                if (c == '.' || c == 'e' || c == 'E') {
+                    is_int = false;
+                    break;
+                }
+            }
+
+            if (is_int) {
+                int contents = [](std::string_view in) {
+                    int out = 0;
+                    bool negative = false;
+                    std::size_t i = 0;
+                    if (in[0] == '-') {
+                        negative = true;
+                        i = 1;
+                    }
+                    for (; i < in.size(); ++i) {
+                        out = out * 10 + (in[i] - '0');
+                    }
+                    return negative ? -out : out;
+                }(value);
+
+                if (first) element_type = ^^int;
+                values.push_back(reflect_constant(contents));
+            } else {
+                // Parse as double
+                double contents = [](std::string_view in) {
+                    double result = 0.0;
+                    double sign = 1.0;
+                    std::size_t i = 0;
+
+                    if (in[0] == '-') {
+                        sign = -1.0;
+                        i = 1;
+                    }
+
+                    while (i < in.size() && in[i] >= '0' && in[i] <= '9') {
+                        result = result * 10.0 + (in[i] - '0');
+                        ++i;
+                    }
+
+                    if (i < in.size() && in[i] == '.') {
+                        ++i;
+                        double fraction = 0.0;
+                        double divisor = 1.0;
+                        while (i < in.size() && in[i] >= '0' && in[i] <= '9') {
+                            fraction = fraction * 10.0 + (in[i] - '0');
+                            divisor *= 10.0;
+                            ++i;
+                        }
+                        result += fraction / divisor;
+                    }
+
+                    return result * sign;
+                }(value);
+
+                if (first) element_type = ^^double;
+                values.push_back(reflect_constant(contents));
+            }
+        } else if (value[0] == '{') {
+            // Nested object in array
+            std::meta::info parsed = parse_json_impl(value);
+            if (first) element_type = std::meta::type_of(parsed);
+            values.push_back(parsed);
+        } else if (value[0] == '[') {
+            // Nested array
+            std::meta::info parsed = parse_json_array_impl(value);
+            if (first) element_type = std::meta::type_of(parsed);
+            values.push_back(parsed);
+        }
+
+        first = false;
+
+        skip_whitespace();
+        if (cursor != end && *cursor == ',')
+            ++cursor;
+    }
+
+    if (cursor == end) throw "unexpected end";
+    expect_consume(']');
+
+    // Create std::array<ElementType, Count> type
+    std::size_t count = values.size() - 1; // -1 because first element is ^^void placeholder
+    auto array_type = std::meta::substitute(^^std::array, {element_type, reflect_constant(count)});
+
+    // Create array instance with values
+    values[0] = array_type;
+    return std::meta::substitute(^^construct_from, values);
+}
+
+/**
+ * @brief Parse JSON and return std::meta::info for the generated type + instance
+ */
+consteval std::meta::info parse_json_impl(std::string_view json) {
+    auto cursor = json.begin();
+    auto end = json.end();
+
+    auto is_whitespace = [](char c) {
+        return c == ' ' || c == '\n' || c == '\t' || c == '\r';
+    };
+
+    auto skip_whitespace = [&]() -> void {
+        while (cursor != end && is_whitespace(*cursor)) cursor++;
+    };
+
+    auto expect_consume = [&](char c) -> void {
+        skip_whitespace();
+        if (cursor == end || *(cursor++) != c) throw "unexpected character";
+    };
+
+    auto parse_until = [&](std::vector<char> delims, std::string &out) -> void {
+        skip_whitespace();
+        while (cursor != end &&
+               !std::ranges::any_of(delims, [&](char c) { return c == *cursor; }))
+            out += *(cursor++);
+    };
+
+    auto parse_delimited = [&](char lhs, std::string &out, char rhs) -> void {
+        skip_whitespace();
+        expect_consume(lhs);
+        parse_until({rhs}, out);
+        expect_consume(rhs);
+    };
+
+    auto parse_value = [&](std::string &out) -> void {
+        skip_whitespace();
+
+        bool quoted = false;
+        unsigned depth = 0;
+        bool in_array = false;
+        while (true) {
+            if (cursor == end) throw "unexpected end of stream";
+            if (is_whitespace(*cursor) && !quoted && depth == 0)
+                break;
+
+            if (depth == 0 && (*cursor == ',' || *cursor == '}' || *cursor == ']'))
+                break;
+            out += *(cursor++);
+
+            if (out.back() == '{')
+                ++depth;
+            else if (out.back() == '}')
+                --depth;
+            else if (out.back() == '[') {
+                in_array = true;
+                ++depth;
+            } else if (out.back() == ']')
+                --depth;
+            else if (out.back() == '"') {
+                if (quoted && depth == 0)
+                    break;
+                quoted = true;
+            }
+        }
+    };
+
+    skip_whitespace();
+    expect_consume('{');
+
+    std::vector<std::meta::info> members;
+    std::vector<std::meta::info> values = {^^void};
+
+    using std::meta::reflect_constant, std::meta::reflect_constant_string;
+    while (cursor != end && *cursor != '}') {
+        std::string field_name;
+        std::string value;
+
+        parse_delimited('"', field_name, '"');
+        expect_consume(':');
+        parse_value(value);
+
+        if (value.empty()) throw "expected value";
+        if (cursor == end) throw "unexpected end of stream";
+
+        if (value[0] == '"') {
+            if (value.back() != '"') throw "expected end of string";
+            std::string_view contents(&value[1], value.size() - 2);
+
+            auto dms = std::meta::data_member_spec(^^char const*, {.name=field_name});
+            members.push_back(reflect_constant(dms));
+            values.push_back(reflect_constant_string(contents));
+        } else if (value == "true") {
+            auto dms = std::meta::data_member_spec(^^bool, {.name=field_name});
+            members.push_back(reflect_constant(dms));
+            values.push_back(reflect_constant(true));
+        } else if (value == "false") {
+            auto dms = std::meta::data_member_spec(^^bool, {.name=field_name});
+            members.push_back(reflect_constant(dms));
+            values.push_back(reflect_constant(false));
+        } else if (value == "null") {
+            auto dms = std::meta::data_member_spec(^^std::nullptr_t, {.name=field_name});
+            members.push_back(reflect_constant(dms));
+            values.push_back(reflect_constant(nullptr));
+        } else if ((value[0] >= '0' && value[0] <= '9') || value[0] == '-') {
+            // Try to parse as integer first
+            bool is_int = true;
+            for (char c : value) {
+                if (c == '.' || c == 'e' || c == 'E') {
+                    is_int = false;
+                    break;
+                }
+            }
+
+            if (is_int) {
+                int contents = [](std::string_view in) {
+                    int out = 0;
+                    bool negative = false;
+                    std::size_t i = 0;
+                    if (in[0] == '-') {
+                        negative = true;
+                        i = 1;
+                    }
+                    for (; i < in.size(); ++i) {
+                        out = out * 10 + (in[i] - '0');
+                    }
+                    return negative ? -out : out;
+                }(value);
+
+                auto dms = std::meta::data_member_spec(^^int, {.name=field_name});
+                members.push_back(reflect_constant(dms));
+                values.push_back(reflect_constant(contents));
+            } else {
+                // Parse as double
+                double contents = [](std::string_view in) {
+                    double result = 0.0;
+                    double sign = 1.0;
+                    std::size_t i = 0;
+
+                    if (in[0] == '-') {
+                        sign = -1.0;
+                        i = 1;
+                    }
+
+                    while (i < in.size() && in[i] >= '0' && in[i] <= '9') {
+                        result = result * 10.0 + (in[i] - '0');
+                        ++i;
+                    }
+
+                    if (i < in.size() && in[i] == '.') {
+                        ++i;
+                        double fraction = 0.0;
+                        double divisor = 1.0;
+                        while (i < in.size() && in[i] >= '0' && in[i] <= '9') {
+                            fraction = fraction * 10.0 + (in[i] - '0');
+                            divisor *= 10.0;
+                            ++i;
+                        }
+                        result += fraction / divisor;
+                    }
+
+                    return result * sign;
+                }(value);
+
+                auto dms = std::meta::data_member_spec(^^double, {.name=field_name});
+                members.push_back(reflect_constant(dms));
+                values.push_back(reflect_constant(contents));
+            }
+        } else if (value[0] == '{') {
+            // Nested object
+            std::meta::info parsed = parse_json_impl(value);
+
+            auto dms = std::meta::data_member_spec(std::meta::type_of(parsed), {.name=field_name});
+            members.push_back(reflect_constant(dms));
+            values.push_back(parsed);
+        } else if (value[0] == '[') {
+            // Array
+            std::meta::info parsed = parse_json_array_impl(value);
+
+            auto dms = std::meta::data_member_spec(std::meta::type_of(parsed), {.name=field_name});
+            members.push_back(reflect_constant(dms));
+            values.push_back(parsed);
+        }
+
+        skip_whitespace();
+        if (cursor != end && *cursor == ',')
+            ++cursor;
+    }
+
+    if (cursor == end) throw "unexpected end";
+    expect_consume('}');
+
+    // The substitute() trick:
+    // 1. Create the type: Cls<member_specs...>
+    values[0] = std::meta::substitute(^^Cls, members);
+    // 2. Create instance: construct_from<Type, values...>
+    return std::meta::substitute(^^construct_from, values);
+}
+
+/**
+ * @brief Main parse_json function - template wrapper
+ */
+template<constevalutil::fixed_string json_str>
+consteval auto parse_json() {
+    constexpr std::meta::info result = parse_json_impl(json_str.view());
+    return [:result:];
+}
+
+/**
+ * @brief JSON validation
+ */
+template<constevalutil::fixed_string json_str>
+consteval bool validate_json() {
+    try {
+        parse_json_impl(json_str.view());
+        return true;
+    } catch (...) {
+        return false;
+    }
+}
+
+} // namespace compile_time
+} // namespace SIMDJSON_IMPLEMENTATION
+} // namespace simdjson
+
+#endif // SIMDJSON_STATIC_REFLECTION
+#endif // SIMDJSON_GENERIC_COMPILE_TIME_JSON_H

include/simdjson/generic/ondemand/deserialize.h

@@ -7,55 +7,8 @@
 #include "simdjson/generic/ondemand/array.h"
 #endif // SIMDJSON_CONDITIONAL_INCLUDE
 
-#include <concepts>
 namespace simdjson {
 
-namespace tag_invoke_fn_ns {
-void tag_invoke();
-
-struct tag_invoke_fn {
-  template <typename Tag, typename... Args>
-    requires requires(Tag tag, Args &&...args) {
-      tag_invoke(std::forward<Tag>(tag), std::forward<Args>(args)...);
-    }
-  constexpr auto operator()(Tag tag, Args &&...args) const
-      noexcept(noexcept(tag_invoke(std::forward<Tag>(tag),
-                                   std::forward<Args>(args)...)))
-          -> decltype(tag_invoke(std::forward<Tag>(tag),
-                                 std::forward<Args>(args)...)) {
-    return tag_invoke(std::forward<Tag>(tag), std::forward<Args>(args)...);
-  }
-};
-} // namespace tag_invoke_fn_ns
-
-inline namespace tag_invoke_ns {
-inline constexpr tag_invoke_fn_ns::tag_invoke_fn tag_invoke = {};
-} // namespace tag_invoke_ns
-
-template <typename Tag, typename... Args>
-concept tag_invocable = requires(Tag tag, Args... args) {
-  tag_invoke(std::forward<Tag>(tag), std::forward<Args>(args)...);
-};
-
-template <typename Tag, typename... Args>
-concept nothrow_tag_invocable =
-    tag_invocable<Tag, Args...> && requires(Tag tag, Args... args) {
-      {
-        tag_invoke(std::forward<Tag>(tag), std::forward<Args>(args)...)
-      } noexcept;
-    };
-
-template <typename Tag, typename... Args>
-using tag_invoke_result =
-    std::invoke_result<decltype(tag_invoke), Tag, Args...>;
-
-template <typename Tag, typename... Args>
-using tag_invoke_result_t =
-    std::invoke_result_t<decltype(tag_invoke), Tag, Args...>;
-
-template <auto &Tag> using tag_t = std::decay_t<decltype(Tag)>;
-
-
 struct deserialize_tag;
 
 /// These types are deserializable in a built-in way

include/simdjson/generic/ondemand/document-inl.h

@@ -141,7 +141,7 @@ simdjson_inline simdjson_result<std::string_view> document::get_string(bool allo
   return get_root_value_iterator().get_root_string(true, allow_replacement);
 }
 template <typename string_type>
-simdjson_inline error_code document::get_string(string_type& receiver, bool allow_replacement) noexcept {
+simdjson_warn_unused simdjson_inline error_code document::get_string(string_type& receiver, bool allow_replacement) noexcept {
   return get_root_value_iterator().get_root_string(receiver, true, allow_replacement);
 }
 simdjson_inline simdjson_result<std::string_view> document::get_wobbly_string() noexcept {
@@ -167,15 +167,15 @@ template<> simdjson_inline simdjson_result<int64_t> document::get() & noexcept {
 template<> simdjson_inline simdjson_result<bool> document::get() & noexcept { return get_bool(); }
 template<> simdjson_inline simdjson_result<value> document::get() & noexcept { return get_value(); }
 
-template<> simdjson_inline error_code document::get(array& out) & noexcept { return get_array().get(out); }
-template<> simdjson_inline error_code document::get(object& out) & noexcept { return get_object().get(out); }
-template<> simdjson_inline error_code document::get(raw_json_string& out) & noexcept { return get_raw_json_string().get(out); }
-template<> simdjson_inline error_code document::get(std::string_view& out) & noexcept { return get_string(false).get(out); }
-template<> simdjson_inline error_code document::get(double& out) & noexcept { return get_double().get(out); }
-template<> simdjson_inline error_code document::get(uint64_t& out) & noexcept { return get_uint64().get(out); }
-template<> simdjson_inline error_code document::get(int64_t& out) & noexcept { return get_int64().get(out); }
-template<> simdjson_inline error_code document::get(bool& out) & noexcept { return get_bool().get(out); }
-template<> simdjson_inline error_code document::get(value& out) & noexcept { return get_value().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(array& out) & noexcept { return get_array().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(object& out) & noexcept { return get_object().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(raw_json_string& out) & noexcept { return get_raw_json_string().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(std::string_view& out) & noexcept { return get_string(false).get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(double& out) & noexcept { return get_double().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(uint64_t& out) & noexcept { return get_uint64().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(int64_t& out) & noexcept { return get_int64().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(bool& out) & noexcept { return get_bool().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code document::get(value& out) & noexcept { return get_value().get(out); }
 
 template<> simdjson_deprecated simdjson_inline simdjson_result<raw_json_string> document::get() && noexcept { return get_raw_json_string(); }
 template<> simdjson_deprecated simdjson_inline simdjson_result<std::string_view> document::get() && noexcept { return get_string(false); }
@@ -245,7 +245,7 @@ simdjson_inline simdjson_result<value> document::operator[](const char *key) & n
   return start_or_resume_object()[key];
 }
 
-simdjson_inline error_code document::consume() noexcept {
+simdjson_warn_unused simdjson_inline error_code document::consume() noexcept {
   bool scalar = false;
   auto error = is_scalar().get(scalar);
   if(error) { return error; }
@@ -347,6 +347,54 @@ simdjson_inline simdjson_result<value> document::at_path(std::string_view json_p
   }
 }
 
+
+
+#if SIMDJSON_SUPPORTS_CONCEPTS && SIMDJSON_STATIC_REFLECTION
+
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_inline error_code document::extract_into(T& out) & noexcept {
+  // Helper to check if a field name matches any of the requested fields
+  auto should_extract = [](std::string_view field_name) constexpr -> bool {
+    return ((FieldNames.view() == field_name) || ...);
+  };
+
+  // Iterate through all members of T using reflection
+  template for (constexpr auto mem : std::define_static_array(
+      std::meta::nonstatic_data_members_of(^^T, std::meta::access_context::unchecked()))) {
+
+    if constexpr (!std::meta::is_const(mem) && std::meta::is_public(mem)) {
+      constexpr std::string_view key = std::define_static_string(std::meta::identifier_of(mem));
+
+      // Only extract this field if it's in our list of requested fields
+      if constexpr (should_extract(key)) {
+        // Try to find and extract the field
+        if constexpr (concepts::optional_type<decltype(out.[:mem:])>) {
+          // For optional fields, it's ok if they're missing
+          auto field_result = find_field_unordered(key);
+          if (!field_result.error()) {
+            auto error = field_result.get(out.[:mem:]);
+            if (error && error != NO_SUCH_FIELD) {
+              return error;
+            }
+          } else if (field_result.error() != NO_SUCH_FIELD) {
+            return field_result.error();
+          } else {
+            out.[:mem:].reset();
+          }
+        } else {
+          // For required fields (in the requested list), fail if missing
+          SIMDJSON_TRY((*this)[key].get(out.[:mem:]));
+        }
+      }
+    }
+  };
+
+  return SUCCESS;
+}
+
+#endif // SIMDJSON_SUPPORTS_CONCEPTS && SIMDJSON_STATIC_REFLECTION
+
 } // namespace ondemand
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
@@ -454,7 +502,7 @@ simdjson_inline simdjson_result<std::string_view> simdjson_result<SIMDJSON_IMPLE
   return first.get_string(allow_replacement);
 }
 template <typename string_type>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get_string(string_type& receiver, bool allow_replacement) noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get_string(string_type& receiver, bool allow_replacement) noexcept {
   if (error()) { return error(); }
   return first.get_string(receiver, allow_replacement);
 }
@@ -490,12 +538,12 @@ simdjson_deprecated simdjson_inline simdjson_result<T> simdjson_result<SIMDJSON_
   return std::forward<SIMDJSON_IMPLEMENTATION::ondemand::document>(first).get<T>();
 }
 template<typename T>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get(T &out) & noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get(T &out) & noexcept {
   if (error()) { return error(); }
   return first.get<T>(out);
 }
 template<typename T>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get(T &out) && noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get(T &out) && noexcept {
   if (error()) { return error(); }
   return std::forward<SIMDJSON_IMPLEMENTATION::ondemand::document>(first).get<T>(out);
 }
@@ -505,8 +553,8 @@ template<> simdjson_deprecated simdjson_inline simdjson_result<SIMDJSON_IMPLEMEN
   if (error()) { return error(); }
   return std::forward<SIMDJSON_IMPLEMENTATION::ondemand::document>(first);
 }
-template<> simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get<SIMDJSON_IMPLEMENTATION::ondemand::document>(SIMDJSON_IMPLEMENTATION::ondemand::document &out) & noexcept = delete;
-template<> simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get<SIMDJSON_IMPLEMENTATION::ondemand::document>(SIMDJSON_IMPLEMENTATION::ondemand::document &out) && noexcept {
+template<> simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get<SIMDJSON_IMPLEMENTATION::ondemand::document>(SIMDJSON_IMPLEMENTATION::ondemand::document &out) & noexcept = delete;
+template<> simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::get<SIMDJSON_IMPLEMENTATION::ondemand::document>(SIMDJSON_IMPLEMENTATION::ondemand::document &out) && noexcept {
   if (error()) { return error(); }
   out = std::forward<SIMDJSON_IMPLEMENTATION::ondemand::document>(first);
   return SUCCESS;
@@ -624,6 +672,15 @@ simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::value> simdjs
   return first.at_path(json_path);
 }
 
+#if SIMDJSON_STATIC_REFLECTION
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document>::extract_into(T& out) & noexcept {
+  if (error()) { return error(); }
+  return first.extract_into<FieldNames...>(out);
+}
+#endif // SIMDJSON_STATIC_REFLECTION
+
 } // namespace simdjson
 
 
@@ -658,7 +715,7 @@ simdjson_inline simdjson_result<double> document_reference::get_double() noexcep
 simdjson_inline simdjson_result<double> document_reference::get_double_in_string() noexcept { return doc->get_root_value_iterator().get_root_double(false); }
 simdjson_inline simdjson_result<std::string_view> document_reference::get_string(bool allow_replacement) noexcept { return doc->get_root_value_iterator().get_root_string(false, allow_replacement); }
 template <typename string_type>
-simdjson_inline error_code document_reference::get_string(string_type& receiver, bool allow_replacement) noexcept { return doc->get_root_value_iterator().get_root_string(receiver, false, allow_replacement); }
+simdjson_warn_unused simdjson_inline error_code document_reference::get_string(string_type& receiver, bool allow_replacement) noexcept { return doc->get_root_value_iterator().get_root_string(receiver, false, allow_replacement); }
 simdjson_inline simdjson_result<std::string_view> document_reference::get_wobbly_string() noexcept { return doc->get_root_value_iterator().get_root_wobbly_string(false); }
 simdjson_inline simdjson_result<raw_json_string> document_reference::get_raw_json_string() noexcept { return doc->get_root_value_iterator().get_root_raw_json_string(false); }
 simdjson_inline simdjson_result<bool> document_reference::get_bool() noexcept { return doc->get_root_value_iterator().get_root_bool(false); }
@@ -711,7 +768,13 @@ simdjson_inline simdjson_result<value> document_reference::at_pointer(std::strin
 simdjson_inline simdjson_result<value> document_reference::at_path(std::string_view json_path) noexcept { return doc->at_path(json_path); }
 simdjson_inline simdjson_result<std::string_view> document_reference::raw_json() noexcept { return doc->raw_json();}
 simdjson_inline document_reference::operator document&() const noexcept { return *doc; }
-
+#if SIMDJSON_SUPPORTS_CONCEPTS && SIMDJSON_STATIC_REFLECTION
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_inline error_code document_reference::extract_into(T& out) & noexcept {
+  return doc->extract_into<FieldNames...>(out);
+}
+#endif // SIMDJSON_SUPPORTS_CONCEPTS && SIMDJSON_STATIC_REFLECTION
 } // namespace ondemand
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
@@ -808,7 +871,7 @@ simdjson_inline simdjson_result<std::string_view> simdjson_result<SIMDJSON_IMPLE
   return first.get_string(allow_replacement);
 }
 template <typename string_type>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get_string(string_type& receiver, bool allow_replacement) noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get_string(string_type& receiver, bool allow_replacement) noexcept {
   if (error()) { return error(); }
   return first.get_string(receiver, allow_replacement);
 }
@@ -843,12 +906,12 @@ simdjson_inline simdjson_result<T> simdjson_result<SIMDJSON_IMPLEMENTATION::onde
   return std::forward<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>(first).get<T>();
 }
 template <class T>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(T &out) & noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(T &out) & noexcept {
   if (error()) { return error(); }
   return first.get<T>(out);
 }
 template <class T>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(T &out) && noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(T &out) && noexcept {
   if (error()) { return error(); }
   return std::forward<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>(first).get<T>(out);
 }
@@ -865,13 +928,13 @@ simdjson_inline simdjson_result<bool> simdjson_result<SIMDJSON_IMPLEMENTATION::o
   return first.is_string();
 }
 template <>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(SIMDJSON_IMPLEMENTATION::ondemand::document_reference &out) & noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(SIMDJSON_IMPLEMENTATION::ondemand::document_reference &out) & noexcept {
   if (error()) { return error(); }
   out = first;
   return SUCCESS;
 }
 template <>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(SIMDJSON_IMPLEMENTATION::ondemand::document_reference &out) && noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::get(SIMDJSON_IMPLEMENTATION::ondemand::document_reference &out) && noexcept {
   if (error()) { return error(); }
   out = first;
   return SUCCESS;
@@ -959,7 +1022,14 @@ simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::value> simdjs
   }
   return first.at_path(json_path);
 }
-
+#if SIMDJSON_STATIC_REFLECTION
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::document_reference>::extract_into(T& out) & noexcept {
+  if (error()) { return error(); }
+  return first.extract_into<FieldNames...>(out);
+}
+#endif // SIMDJSON_STATIC_REFLECTION
 } // namespace simdjson
 
 #endif // SIMDJSON_GENERIC_ONDEMAND_DOCUMENT_INL_H

include/simdjson/generic/ondemand/document.h

@@ -117,7 +117,7 @@ public:
    * @returns INCORRECT_TYPE if the JSON value is not a string. Otherwise, we return SUCCESS.
    */
   template <typename string_type>
-  simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
+  simdjson_warn_unused simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
   /**
    * Cast this JSON value to a string.
    *
@@ -228,7 +228,7 @@ public:
    * @returns SUCCESS If the parse succeeded and the out parameter was set to the value.
    */
   template<typename T>
-  simdjson_inline error_code get(T &out) &
+  simdjson_warn_unused simdjson_inline error_code get(T &out) &
 #if SIMDJSON_SUPPORTS_CONCEPTS
     noexcept(custom_deserializable<T, document> ? nothrow_custom_deserializable<T, document> : true)
 #else
@@ -725,11 +725,41 @@ public:
    * the JSON document.
    */
   simdjson_inline simdjson_result<std::string_view> raw_json() noexcept;
+
+#if SIMDJSON_STATIC_REFLECTION
+  /**
+   * Extract only specific fields from the JSON object into a struct.
+   *
+   * This allows selective deserialization of only the fields you need,
+   * potentially improving performance by skipping unwanted fields.
+   *
+   * Example:
+   * ```c++
+   * struct Car {
+   *   std::string make;
+   *   std::string model;
+   *   int year;
+   *   double price;
+   * };
+   *
+   * Car car;
+   * doc.extract_into<"make", "model">(car);
+   * // Only 'make' and 'model' fields are extracted from JSON
+   * ```
+   *
+   * @tparam FieldNames Compile-time string literals specifying which fields to extract
+   * @param out The output struct to populate with selected fields
+   * @returns SUCCESS on success, or an error code if a required field is missing or has wrong type
+   */
+  template<constevalutil::fixed_string... FieldNames, typename T>
+    requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+  simdjson_warn_unused simdjson_inline error_code extract_into(T& out) & noexcept;
+#endif // SIMDJSON_STATIC_REFLECTION
 protected:
   /**
    * Consumes the document.
    */
-  simdjson_inline error_code consume() noexcept;
+  simdjson_warn_unused simdjson_inline error_code consume() noexcept;
 
   simdjson_inline document(ondemand::json_iterator &&iter) noexcept;
   simdjson_inline const uint8_t *text(uint32_t idx) const noexcept;
@@ -782,7 +812,7 @@ public:
   simdjson_inline simdjson_result<double> get_double_in_string() noexcept;
   simdjson_inline simdjson_result<std::string_view> get_string(bool allow_replacement = false) noexcept;
   template <typename string_type>
-  simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
+  simdjson_warn_unused simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
   simdjson_inline simdjson_result<std::string_view> get_wobbly_string() noexcept;
   simdjson_inline simdjson_result<raw_json_string> get_raw_json_string() noexcept;
   simdjson_inline simdjson_result<bool> get_bool() noexcept;
@@ -826,7 +856,7 @@ public:
    * @returns SUCCESS If the parse succeeded and the out parameter was set to the value.
    */
   template<typename T>
-  simdjson_inline error_code get(T &out) &
+  simdjson_warn_unused simdjson_inline error_code get(T &out) &
 #if SIMDJSON_SUPPORTS_CONCEPTS
     noexcept(custom_deserializable<T, document> ? nothrow_custom_deserializable<T, document_reference> : true)
 #else
@@ -861,6 +891,11 @@ public:
   /** @overload template<typename T> error_code get(T &out) & noexcept */
   template<typename T> simdjson_inline error_code get(T &out) && noexcept;
   simdjson_inline simdjson_result<std::string_view> raw_json() noexcept;
+#if SIMDJSON_STATIC_REFLECTION
+  template<constevalutil::fixed_string... FieldNames, typename T>
+    requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+  simdjson_warn_unused simdjson_inline error_code extract_into(T& out) & noexcept;
+#endif // SIMDJSON_STATIC_REFLECTION
   simdjson_inline operator document&() const noexcept;
 #if SIMDJSON_EXCEPTIONS
   template <class T>
@@ -929,7 +964,7 @@ public:
   simdjson_inline simdjson_result<double> get_double_in_string() noexcept;
   simdjson_inline simdjson_result<std::string_view> get_string(bool allow_replacement = false) noexcept;
   template <typename string_type>
-  simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
+  simdjson_warn_unused simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
   simdjson_inline simdjson_result<std::string_view> get_wobbly_string() noexcept;
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::raw_json_string> get_raw_json_string() noexcept;
   simdjson_inline simdjson_result<bool> get_bool() noexcept;
@@ -984,6 +1019,11 @@ public:
 
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::value> at_pointer(std::string_view json_pointer) noexcept;
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::value> at_path(std::string_view json_path) noexcept;
+#if SIMDJSON_STATIC_REFLECTION
+  template<constevalutil::fixed_string... FieldNames, typename T>
+    requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+  simdjson_warn_unused simdjson_inline error_code extract_into(T& out) & noexcept;
+#endif // SIMDJSON_STATIC_REFLECTION
 };
 
 
@@ -1010,7 +1050,7 @@ public:
   simdjson_inline simdjson_result<double> get_double_in_string() noexcept;
   simdjson_inline simdjson_result<std::string_view> get_string(bool allow_replacement = false) noexcept;
   template <typename string_type>
-  simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
+  simdjson_warn_unused simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
   simdjson_inline simdjson_result<std::string_view> get_wobbly_string() noexcept;
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::raw_json_string> get_raw_json_string() noexcept;
   simdjson_inline simdjson_result<bool> get_bool() noexcept;
@@ -1061,6 +1101,11 @@ public:
 
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::value> at_pointer(std::string_view json_pointer) noexcept;
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::value> at_path(std::string_view json_path) noexcept;
+#if SIMDJSON_STATIC_REFLECTION
+  template<constevalutil::fixed_string... FieldNames, typename T>
+    requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+  simdjson_warn_unused simdjson_inline error_code extract_into(T& out) & noexcept;
+#endif // SIMDJSON_STATIC_REFLECTION
 };
 
 

include/simdjson/generic/ondemand/document_stream-inl.h

@@ -312,7 +312,10 @@ inline void document_stream::next_document() noexcept {
   // Always set depth=1 at the start of document
   doc.iter._depth = 1;
   // consume comma if comma separated is allowed
-  if (allow_comma_separated) { doc.iter.consume_character(','); }
+  if (allow_comma_separated) {
+    error_code ignored = doc.iter.consume_character(',');
+    static_cast<void>(ignored); // ignored on purpose
+  }
   // Resets the string buffer at the beginning, thus invalidating the strings.
   doc.iter._string_buf_loc = parser->string_buf.get();
   doc.iter._root = doc.iter.position();

include/simdjson/generic/ondemand/field-inl.h

@@ -114,7 +114,7 @@ simdjson_inline simdjson_result<std::string_view> simdjson_result<SIMDJSON_IMPLE
 }
 
 template<typename string_type>
-simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::field>::unescaped_key(string_type &receiver, bool allow_replacement) noexcept {
+simdjson_warn_unused simdjson_inline error_code simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::field>::unescaped_key(string_type &receiver, bool allow_replacement) noexcept {
   if (error()) { return error(); }
   return first.unescaped_key(receiver, allow_replacement);
 }

include/simdjson/generic/ondemand/json_builder.h

@@ -13,7 +13,7 @@
 
 #include <charconv>
 #include <cstring>
-#include <experimental/meta>
+#include <meta>
 #include <memory>
 #include <optional>
 #include <string_view>
@@ -25,30 +25,21 @@ namespace simdjson {
 namespace SIMDJSON_IMPLEMENTATION {
 namespace builder {
 
-// Concept that checks if a type is a container but not a string (because
-// strings handling must be handled differently)
-template <typename T>
-concept container_but_not_string =
-    requires(T a) {
-      { a.size() } -> std::convertible_to<std::size_t>;
-      {
-        a[std::declval<std::size_t>()]
-      }; // check if elements are accessible for the subscript operator
-    } && !std::is_same_v<T, std::string> &&
-    !std::is_same_v<T, std::string_view> && !std::is_same_v<T, const char *>;
-
 template <class T>
-  requires(container_but_not_string<T>)
+  requires(concepts::container_but_not_string<T> && !require_custom_serialization<T>)
 constexpr void atom(string_builder &b, const T &t) {
-  if (t.size() == 0) {
+  auto it = t.begin();
+  auto end = t.end();
+  if (it == end) {
     b.append_raw("[]");
     return;
   }
   b.append('[');
-  atom(b, t[0]);
-  for (size_t i = 1; i < t.size(); ++i) {
+  atom(b, *it);
+  ++it;
+  for (; it != end; ++it) {
     b.append(',');
-    atom(b, t[i]);
+    atom(b, *it);
   }
   b.append(']');
 }
@@ -63,6 +54,7 @@ constexpr void atom(string_builder &b, const T &t) {
 }
 
 template <concepts::string_view_keyed_map T>
+  requires(!require_custom_serialization<T>)
 constexpr void atom(string_builder &b, const T &m) {
   if (m.empty()) {
     b.append_raw("{}");
@@ -91,7 +83,7 @@ constexpr void atom(string_builder &b, const number_type t) {
 }
 
 template <class T>
-  requires(std::is_class_v<T> && !container_but_not_string<T> &&
+  requires(std::is_class_v<T> && !concepts::container_but_not_string<T> &&
            !concepts::string_view_keyed_map<T> &&
            !concepts::optional_type<T> &&
            !concepts::smart_pointer<T> &&
@@ -99,7 +91,7 @@ template <class T>
            !std::is_same_v<T, std::string> &&
            !std::is_same_v<T, std::string_view> &&
            !std::is_same_v<T, const char*> &&
-           !std::is_same_v<T, char>)
+           !std::is_same_v<T, char> && !require_custom_serialization<T>)
 constexpr void atom(string_builder &b, const T &t) {
   int i = 0;
   b.append('{');
@@ -117,6 +109,7 @@ constexpr void atom(string_builder &b, const T &t) {
 
 // Support for optional types (std::optional, etc.)
 template <concepts::optional_type T>
+  requires(!require_custom_serialization<T>)
 constexpr void atom(string_builder &b, const T &opt) {
   if (opt) {
     atom(b, opt.value());
@@ -127,6 +120,7 @@ constexpr void atom(string_builder &b, const T &opt) {
 
 // Support for smart pointers (std::unique_ptr, std::shared_ptr, etc.)
 template <concepts::smart_pointer T>
+  requires(!require_custom_serialization<T>)
 constexpr void atom(string_builder &b, const T &ptr) {
   if (ptr) {
     atom(b, *ptr);
@@ -137,7 +131,7 @@ constexpr void atom(string_builder &b, const T &ptr) {
 
 // Support for enums - serialize as string representation using expand approach from P2996R12
 template <typename T>
-  requires(std::is_enum_v<T>)
+  requires(std::is_enum_v<T> && !require_custom_serialization<T>)
 void atom(string_builder &b, const T &e) {
 #if SIMDJSON_STATIC_REFLECTION
   constexpr auto enumerators = std::define_static_array(std::meta::enumerators_of(^^T));
@@ -158,10 +152,10 @@ void atom(string_builder &b, const T &e) {
 
 // Support for appendable containers that don't have operator[] (sets, etc.)
 template <concepts::appendable_containers T>
-  requires(!container_but_not_string<T> && !concepts::string_view_keyed_map<T> &&
+  requires(!concepts::container_but_not_string<T> && !concepts::string_view_keyed_map<T> &&
            !concepts::optional_type<T> && !concepts::smart_pointer<T> &&
            !std::is_same_v<T, std::string> &&
-           !std::is_same_v<T, std::string_view> && !std::is_same_v<T, const char*>)
+           !std::is_same_v<T, std::string_view> && !std::is_same_v<T, const char*> && !require_custom_serialization<T>)
 constexpr void atom(string_builder &b, const T &container) {
   if (container.empty()) {
     b.append_raw("[]");
@@ -196,32 +190,35 @@ void append(string_builder &b, const T &t) {
 }
 
 template <concepts::optional_type T>
+  requires(!require_custom_serialization<T>)
 void append(string_builder &b, const T &t) {
   atom(b, t);
 }
 
 template <concepts::smart_pointer T>
+  requires(!require_custom_serialization<T>)
 void append(string_builder &b, const T &t) {
   atom(b, t);
 }
 
 template <concepts::appendable_containers T>
-  requires(!container_but_not_string<T> && !concepts::string_view_keyed_map<T> &&
+  requires(!concepts::container_but_not_string<T> && !concepts::string_view_keyed_map<T> &&
            !concepts::optional_type<T> && !concepts::smart_pointer<T> &&
            !std::is_same_v<T, std::string> &&
-           !std::is_same_v<T, std::string_view> && !std::is_same_v<T, const char*>)
+           !std::is_same_v<T, std::string_view> && !std::is_same_v<T, const char*> && !require_custom_serialization<T>)
 void append(string_builder &b, const T &t) {
   atom(b, t);
 }
 
 template <concepts::string_view_keyed_map T>
+  requires(!require_custom_serialization<T>)
 void append(string_builder &b, const T &t) {
   atom(b, t);
 }
 
 // works for struct
 template <class Z>
-  requires(std::is_class_v<Z> && !container_but_not_string<Z> &&
+  requires(std::is_class_v<Z> && !concepts::container_but_not_string<Z> &&
            !concepts::string_view_keyed_map<Z> &&
            !concepts::optional_type<Z> &&
            !concepts::smart_pointer<Z> &&
@@ -229,7 +226,7 @@ template <class Z>
            !std::is_same_v<Z, std::string> &&
            !std::is_same_v<Z, std::string_view> &&
            !std::is_same_v<Z, const char*> &&
-           !std::is_same_v<Z, char>)
+           !std::is_same_v<Z, char> && !require_custom_serialization<Z>)
 void append(string_builder &b, const Z &z) {
   int i = 0;
   b.append('{');
@@ -245,25 +242,35 @@ void append(string_builder &b, const Z &z) {
   b.append('}');
 }
 
-// works for container
+// works for container that have begin() and end() iterators
 template <class Z>
-  requires(container_but_not_string<Z>)
+  requires(concepts::container_but_not_string<Z> && !require_custom_serialization<Z>)
 void append(string_builder &b, const Z &z) {
-  if (z.size() == 0) {
+  auto it = z.begin();
+  auto end = z.end();
+  if (it == end) {
     b.append_raw("[]");
     return;
   }
   b.append('[');
-  atom(b, z[0]);
-  for (size_t i = 1; i < z.size(); ++i) {
+  atom(b, *it);
+  ++it;
+  for (; it != end; ++it) {
     b.append(',');
-    atom(b, z[i]);
+    atom(b, *it);
   }
   b.append(']');
 }
 
 template <class Z>
-simdjson_result<std::string> to_json_string(const Z &z, size_t initial_capacity = 1024) {
+  requires (require_custom_serialization<Z>)
+void append(string_builder &b, const Z &z) {
+  b.append(z);
+}
+
+
+template <class Z>
+simdjson_warn_unused simdjson_result<std::string> to_json_string(const Z &z, size_t initial_capacity = string_builder::DEFAULT_INITIAL_CAPACITY) {
   string_builder b(initial_capacity);
   append(b, z);
   std::string_view s;
@@ -272,8 +279,8 @@ simdjson_result<std::string> to_json_string(const Z &z, size_t initial_capacity
 }
 
 template <class Z>
-simdjson_error to_json(const Z &z, std::string &s) {
-  string_builder b;
+simdjson_warn_unused simdjson_error to_json(const Z &z, std::string &s, size_t initial_capacity = string_builder::DEFAULT_INITIAL_CAPACITY) {
+  string_builder b(initial_capacity);
   append(b, z);
   std::string_view view;
   if(auto e = b.view().get(view); e) { return e; }
@@ -286,13 +293,88 @@ string_builder& operator<<(string_builder& b, const Z& z) {
   append(b, z);
   return b;
 }
+
+// extract_from: Serialize only specific fields from a struct to JSON
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+void extract_from(string_builder &b, const T &obj) {
+  // Helper to check if a field name matches any of the requested fields
+  auto should_extract = [](std::string_view field_name) constexpr -> bool {
+    return ((FieldNames.view() == field_name) || ...);
+  };
+
+  b.append('{');
+  bool first = true;
+
+  // Iterate through all members of T using reflection
+  template for (constexpr auto mem : std::define_static_array(
+      std::meta::nonstatic_data_members_of(^^T, std::meta::access_context::unchecked()))) {
+
+    if constexpr (std::meta::is_public(mem)) {
+      constexpr std::string_view key = std::define_static_string(std::meta::identifier_of(mem));
+
+      // Only serialize this field if it's in our list of requested fields
+      if constexpr (should_extract(key)) {
+        if (!first) {
+          b.append(',');
+        }
+        first = false;
+
+        // Serialize the key
+        constexpr auto quoted_key = std::define_static_string(constevalutil::consteval_to_quoted_escaped(std::meta::identifier_of(mem)));
+        b.append_raw(quoted_key);
+        b.append(':');
+
+        // Serialize the value
+        atom(b, obj.[:mem:]);
+      }
+    }
+  };
+
+  b.append('}');
+}
+
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_result<std::string> extract_from(const T &obj, size_t initial_capacity = string_builder::DEFAULT_INITIAL_CAPACITY) {
+  string_builder b(initial_capacity);
+  extract_from<FieldNames...>(b, obj);
+  std::string_view s;
+  if(auto e = b.view().get(s); e) { return e; }
+  return std::string(s);
+}
+
 } // namespace builder
 } // namespace SIMDJSON_IMPLEMENTATION
 // Alias the function template to 'to' in the global namespace
 template <class Z>
-simdjson_result<std::string> to_json(const Z &z, size_t initial_capacity = 1024) {
-  return SIMDJSON_IMPLEMENTATION::builder::to_json_string(z, initial_capacity);
+simdjson_warn_unused simdjson_result<std::string> to_json(const Z &z, size_t initial_capacity = SIMDJSON_IMPLEMENTATION::builder::string_builder::DEFAULT_INITIAL_CAPACITY) {
+  SIMDJSON_IMPLEMENTATION::builder::string_builder b(initial_capacity);
+  SIMDJSON_IMPLEMENTATION::builder::append(b, z);
+  std::string_view s;
+  if(auto e = b.view().get(s); e) { return e; }
+  return std::string(s);
 }
+template <class Z>
+simdjson_warn_unused simdjson_error to_json(const Z &z, std::string &s, size_t initial_capacity = SIMDJSON_IMPLEMENTATION::builder::string_builder::DEFAULT_INITIAL_CAPACITY) {
+  SIMDJSON_IMPLEMENTATION::builder::string_builder b(initial_capacity);
+  SIMDJSON_IMPLEMENTATION::builder::append(b, z);
+  std::string_view view;
+  if(auto e = b.view().get(view); e) { return e; }
+  s.assign(view);
+  return SUCCESS;
+}
+// Global namespace function for extract_from
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_result<std::string> extract_from(const T &obj, size_t initial_capacity = SIMDJSON_IMPLEMENTATION::builder::string_builder::DEFAULT_INITIAL_CAPACITY) {
+  SIMDJSON_IMPLEMENTATION::builder::string_builder b(initial_capacity);
+  SIMDJSON_IMPLEMENTATION::builder::extract_from<FieldNames...>(b, obj);
+  std::string_view s;
+  if(auto e = b.view().get(s); e) { return e; }
+  return std::string(s);
+}
+
 } // namespace simdjson
 
 #endif // SIMDJSON_STATIC_REFLECTION

include/simdjson/generic/ondemand/json_iterator-inl.h

@@ -344,7 +344,7 @@ simdjson_inline uint8_t *&json_iterator::string_buf_loc() noexcept {
   return _string_buf_loc;
 }
 
-simdjson_inline error_code json_iterator::report_error(error_code _error, const char *message) noexcept {
+simdjson_warn_unused simdjson_inline error_code json_iterator::report_error(error_code _error, const char *message) noexcept {
   SIMDJSON_ASSUME(_error != SUCCESS && _error != UNINITIALIZED && _error != INCORRECT_TYPE && _error != NO_SUCH_FIELD);
   logger::log_error(*this, message);
   error = _error;
@@ -388,7 +388,7 @@ simdjson_inline void json_iterator::reenter_child(token_position position, depth
   _depth = child_depth;
 }
 
-simdjson_inline error_code json_iterator::consume_character(char c) noexcept {
+simdjson_warn_unused simdjson_inline error_code json_iterator::consume_character(char c) noexcept {
   if (*peek() == c) {
     return_current_and_advance();
     return SUCCESS;
@@ -411,7 +411,7 @@ simdjson_inline void json_iterator::set_start_position(depth_t depth, token_posi
 #endif
 
 
-simdjson_inline error_code json_iterator::optional_error(error_code _error, const char *message) noexcept {
+simdjson_warn_unused simdjson_inline error_code json_iterator::optional_error(error_code _error, const char *message) noexcept {
   SIMDJSON_ASSUME(_error == INCORRECT_TYPE || _error == NO_SUCH_FIELD);
   logger::log_error(*this, message);
   return _error;

include/simdjson/generic/ondemand/json_iterator.h

@@ -238,14 +238,14 @@ public:
    * @param error The error to report. Must not be SUCCESS, UNINITIALIZED, INCORRECT_TYPE, or NO_SUCH_FIELD.
    * @param message An error message to report with the error.
    */
-  simdjson_inline error_code report_error(error_code error, const char *message) noexcept;
+  simdjson_warn_unused simdjson_inline error_code report_error(error_code error, const char *message) noexcept;
 
   /**
    * Log error, but don't stop iteration.
    * @param error The error to report. Must be INCORRECT_TYPE, or NO_SUCH_FIELD.
    * @param message An error message to report with the error.
    */
-  simdjson_inline error_code optional_error(error_code error, const char *message) noexcept;
+  simdjson_warn_unused simdjson_inline error_code optional_error(error_code error, const char *message) noexcept;
 
   /**
    * Take an input in json containing max_len characters and attempt to copy it over to tmpbuf, a buffer with
@@ -265,7 +265,7 @@ public:
 
   simdjson_inline void reenter_child(token_position position, depth_t child_depth) noexcept;
 
-  simdjson_inline error_code consume_character(char c) noexcept;
+  simdjson_warn_unused  simdjson_inline error_code consume_character(char c) noexcept;
 #if SIMDJSON_DEVELOPMENT_CHECKS
   simdjson_inline token_position start_position(depth_t depth) const noexcept;
   simdjson_inline void set_start_position(depth_t depth, token_position position) noexcept;

include/simdjson/generic/ondemand/json_string_builder-inl.h

@@ -42,24 +42,25 @@ namespace simdjson {
 namespace SIMDJSON_IMPLEMENTATION {
 namespace builder {
 
-static SIMDJSON_CONSTEXPR_LAMBDA std::array<uint8_t, 256> json_quotable_character = {
-  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-  1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+static SIMDJSON_CONSTEXPR_LAMBDA std::array<uint8_t, 256>
+    json_quotable_character = {
+        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
 
 /**
 
-A possible SWAR implementation of has_json_escapable_byte. It is not used because
-it is slower than the current implementation. It is kept here for reference (to show
-that we tried it).
+A possible SWAR implementation of has_json_escapable_byte. It is not used
+because it is slower than the current implementation. It is kept here for
+reference (to show that we tried it).
 
 inline bool has_json_escapable_byte(uint64_t x) {
   uint64_t is_ascii = 0x8080808080808080ULL & ~x;
@@ -76,7 +77,7 @@ SIMDJSON_CONSTEXPR_LAMBDA simdjson_inline bool
 simple_needs_escaping(std::string_view v) {
   for (char c : v) {
     // a table lookup is faster than a series of comparisons
-    if(json_quotable_character[static_cast<uint8_t>(c)]) {
+    if (json_quotable_character[static_cast<uint8_t>(c)]) {
       return true;
     }
   }
@@ -117,7 +118,8 @@ simdjson_inline bool fast_needs_escaping(std::string_view view) {
   __m128i running = _mm_setzero_si128();
   for (; i + 15 < view.size(); i += 16) {
 
-    __m128i word = _mm_loadu_si128(reinterpret_cast<const __m128i *>(view.data() + i));
+    __m128i word =
+        _mm_loadu_si128(reinterpret_cast<const __m128i *>(view.data() + i));
     running = _mm_or_si128(running, _mm_cmpeq_epi8(word, _mm_set1_epi8(34)));
     running = _mm_or_si128(running, _mm_cmpeq_epi8(word, _mm_set1_epi8(92)));
     running = _mm_or_si128(
@@ -125,8 +127,8 @@ simdjson_inline bool fast_needs_escaping(std::string_view view) {
                                 _mm_setzero_si128()));
   }
   if (i < view.size()) {
-    __m128i word =
-        _mm_loadu_si128(reinterpret_cast<const __m128i *>(view.data() + view.length() - 16));
+    __m128i word = _mm_loadu_si128(
+        reinterpret_cast<const __m128i *>(view.data() + view.length() - 16));
     running = _mm_or_si128(running, _mm_cmpeq_epi8(word, _mm_set1_epi8(34)));
     running = _mm_or_si128(running, _mm_cmpeq_epi8(word, _mm_set1_epi8(92)));
     running = _mm_or_si128(
@@ -141,7 +143,6 @@ simdjson_inline bool fast_needs_escaping(std::string_view view) {
 }
 #endif
 
-
 SIMDJSON_CONSTEXPR_LAMBDA inline size_t
 find_next_json_quotable_character(const std::string_view view,
                                   size_t location) noexcept {
@@ -156,15 +157,15 @@ find_next_json_quotable_character(const std::string_view view,
 
 SIMDJSON_CONSTEXPR_LAMBDA static std::string_view control_chars[] = {
     "\\u0000", "\\u0001", "\\u0002", "\\u0003", "\\u0004", "\\u0005", "\\u0006",
-    "\\u0007", "\\b", "\\t",     "\\n",     "\\u000b", "\\f",     "\\r",
+    "\\u0007", "\\b",     "\\t",     "\\n",     "\\u000b", "\\f",     "\\r",
     "\\u000e", "\\u000f", "\\u0010", "\\u0011", "\\u0012", "\\u0013", "\\u0014",
     "\\u0015", "\\u0016", "\\u0017", "\\u0018", "\\u0019", "\\u001a", "\\u001b",
     "\\u001c", "\\u001d", "\\u001e", "\\u001f"};
 
-// All Unicode characters may be placed within the quotation marks, except for the
-// characters that MUST be escaped: quotation mark, reverse solidus, and the control
-// characters (U+0000 through U+001F).
-// There are two-character sequence escape representations of some popular characters:
+// All Unicode characters may be placed within the quotation marks, except for
+// the characters that MUST be escaped: quotation mark, reverse solidus, and the
+// control characters (U+0000 through U+001F). There are two-character sequence
+// escape representations of some popular characters:
 // \", \\, \b, \f, \n, \r, \t.
 SIMDJSON_CONSTEXPR_LAMBDA void escape_json_char(char c, char *&out) {
   if (c == '"') {
@@ -284,10 +285,13 @@ simdjson_inline void string_builder::clear() noexcept {
 
 namespace internal {
 
-// We could specialize further for 32-bit integers.
-simdjson_really_inline int int_log2(uint32_t x) { return (63 - leading_zeroes(x | 1)); }
+template <typename number_type, typename = typename std::enable_if<
+                                    std::is_unsigned<number_type>::value>::type>
+simdjson_really_inline int int_log2(number_type x) {
+  return 63 - leading_zeroes(uint64_t(x) | 1);
+}
 
-simdjson_really_inline int fast_digit_count(uint32_t x) {
+simdjson_really_inline int fast_digit_count_32(uint32_t x) {
   static uint64_t table[] = {
       4294967296,  8589934582,  8589934582,  8589934582,  12884901788,
       12884901788, 12884901788, 17179868184, 17179868184, 17179868184,
@@ -299,9 +303,7 @@ simdjson_really_inline int fast_digit_count(uint32_t x) {
   return uint32_t((x + table[int_log2(x)]) >> 32);
 }
 
-simdjson_really_inline int int_log2(uint64_t x) { return 63 - leading_zeroes(x | 1); }
-
-simdjson_really_inline int fast_digit_count(uint64_t x) {
+simdjson_really_inline int fast_digit_count_64(uint64_t x) {
   static uint64_t table[] = {9,
                              99,
                              999,
@@ -332,26 +334,31 @@ simdjson_really_inline size_t digit_count(number_type v) noexcept {
   static_assert(sizeof(number_type) == 8 || sizeof(number_type) == 4 ||
                     sizeof(number_type) == 2 || sizeof(number_type) == 1,
                 "We only support 8-bit, 16-bit, 32-bit and 64-bit numbers");
-  return fast_digit_count(v);
+  SIMDJSON_IF_CONSTEXPR(sizeof(number_type) <= 4) {
+    return fast_digit_count_32(static_cast<uint32_t>(v));
+  }
+  else {
+    return fast_digit_count_64(static_cast<uint64_t>(v));
+  }
 }
 static const char decimal_table[200] = {
-  0x30, 0x30, 0x30, 0x31, 0x30, 0x32, 0x30, 0x33, 0x30, 0x34, 0x30, 0x35,
-  0x30, 0x36, 0x30, 0x37, 0x30, 0x38, 0x30, 0x39, 0x31, 0x30, 0x31, 0x31,
-  0x31, 0x32, 0x31, 0x33, 0x31, 0x34, 0x31, 0x35, 0x31, 0x36, 0x31, 0x37,
-  0x31, 0x38, 0x31, 0x39, 0x32, 0x30, 0x32, 0x31, 0x32, 0x32, 0x32, 0x33,
-  0x32, 0x34, 0x32, 0x35, 0x32, 0x36, 0x32, 0x37, 0x32, 0x38, 0x32, 0x39,
-  0x33, 0x30, 0x33, 0x31, 0x33, 0x32, 0x33, 0x33, 0x33, 0x34, 0x33, 0x35,
-  0x33, 0x36, 0x33, 0x37, 0x33, 0x38, 0x33, 0x39, 0x34, 0x30, 0x34, 0x31,
-  0x34, 0x32, 0x34, 0x33, 0x34, 0x34, 0x34, 0x35, 0x34, 0x36, 0x34, 0x37,
-  0x34, 0x38, 0x34, 0x39, 0x35, 0x30, 0x35, 0x31, 0x35, 0x32, 0x35, 0x33,
-  0x35, 0x34, 0x35, 0x35, 0x35, 0x36, 0x35, 0x37, 0x35, 0x38, 0x35, 0x39,
-  0x36, 0x30, 0x36, 0x31, 0x36, 0x32, 0x36, 0x33, 0x36, 0x34, 0x36, 0x35,
-  0x36, 0x36, 0x36, 0x37, 0x36, 0x38, 0x36, 0x39, 0x37, 0x30, 0x37, 0x31,
-  0x37, 0x32, 0x37, 0x33, 0x37, 0x34, 0x37, 0x35, 0x37, 0x36, 0x37, 0x37,
-  0x37, 0x38, 0x37, 0x39, 0x38, 0x30, 0x38, 0x31, 0x38, 0x32, 0x38, 0x33,
-  0x38, 0x34, 0x38, 0x35, 0x38, 0x36, 0x38, 0x37, 0x38, 0x38, 0x38, 0x39,
-  0x39, 0x30, 0x39, 0x31, 0x39, 0x32, 0x39, 0x33, 0x39, 0x34, 0x39, 0x35,
-  0x39, 0x36, 0x39, 0x37, 0x39, 0x38, 0x39, 0x39,
+    0x30, 0x30, 0x30, 0x31, 0x30, 0x32, 0x30, 0x33, 0x30, 0x34, 0x30, 0x35,
+    0x30, 0x36, 0x30, 0x37, 0x30, 0x38, 0x30, 0x39, 0x31, 0x30, 0x31, 0x31,
+    0x31, 0x32, 0x31, 0x33, 0x31, 0x34, 0x31, 0x35, 0x31, 0x36, 0x31, 0x37,
+    0x31, 0x38, 0x31, 0x39, 0x32, 0x30, 0x32, 0x31, 0x32, 0x32, 0x32, 0x33,
+    0x32, 0x34, 0x32, 0x35, 0x32, 0x36, 0x32, 0x37, 0x32, 0x38, 0x32, 0x39,
+    0x33, 0x30, 0x33, 0x31, 0x33, 0x32, 0x33, 0x33, 0x33, 0x34, 0x33, 0x35,
+    0x33, 0x36, 0x33, 0x37, 0x33, 0x38, 0x33, 0x39, 0x34, 0x30, 0x34, 0x31,
+    0x34, 0x32, 0x34, 0x33, 0x34, 0x34, 0x34, 0x35, 0x34, 0x36, 0x34, 0x37,
+    0x34, 0x38, 0x34, 0x39, 0x35, 0x30, 0x35, 0x31, 0x35, 0x32, 0x35, 0x33,
+    0x35, 0x34, 0x35, 0x35, 0x35, 0x36, 0x35, 0x37, 0x35, 0x38, 0x35, 0x39,
+    0x36, 0x30, 0x36, 0x31, 0x36, 0x32, 0x36, 0x33, 0x36, 0x34, 0x36, 0x35,
+    0x36, 0x36, 0x36, 0x37, 0x36, 0x38, 0x36, 0x39, 0x37, 0x30, 0x37, 0x31,
+    0x37, 0x32, 0x37, 0x33, 0x37, 0x34, 0x37, 0x35, 0x37, 0x36, 0x37, 0x37,
+    0x37, 0x38, 0x37, 0x39, 0x38, 0x30, 0x38, 0x31, 0x38, 0x32, 0x38, 0x33,
+    0x38, 0x34, 0x38, 0x35, 0x38, 0x36, 0x38, 0x37, 0x38, 0x38, 0x38, 0x39,
+    0x39, 0x30, 0x39, 0x31, 0x39, 0x32, 0x39, 0x33, 0x39, 0x34, 0x39, 0x35,
+    0x39, 0x36, 0x39, 0x37, 0x39, 0x38, 0x39, 0x39,
 };
 } // namespace internal
 
@@ -387,7 +394,7 @@ simdjson_inline void string_builder::append(number_type v) noexcept {
       size_t dc = internal::digit_count(pv);
       char *write_pointer = buffer.get() + position + dc - 1;
       while (pv >= 100) {
-        memcpy(write_pointer - 1, &internal::decimal_table[(pv % 100)*2], 2);
+        memcpy(write_pointer - 1, &internal::decimal_table[(pv % 100) * 2], 2);
         write_pointer -= 2;
         pv /= 100;
       }
@@ -414,7 +421,7 @@ simdjson_inline void string_builder::append(number_type v) noexcept {
       }
       char *write_pointer = buffer.get() + position + dc - 1;
       while (pv >= 100) {
-        memcpy(write_pointer - 1, &internal::decimal_table[(pv % 100)*2], 2);
+        memcpy(write_pointer - 1, &internal::decimal_table[(pv % 100) * 2], 2);
         write_pointer -= 2;
         pv /= 100;
       }
@@ -466,10 +473,17 @@ string_builder::escape_and_append_with_quotes(char input) noexcept {
   }
 }
 
-simdjson_inline void string_builder::escape_and_append_with_quotes(const char* input)  noexcept {
+simdjson_inline void
+string_builder::escape_and_append_with_quotes(const char *input) noexcept {
   std::string_view cinput(input);
   escape_and_append_with_quotes(cinput);
 }
+#if SIMDJSON_SUPPORTS_CONCEPTS
+template <constevalutil::fixed_string key>
+simdjson_inline void string_builder::escape_and_append_with_quotes() noexcept {
+  escape_and_append_with_quotes(constevalutil::string_constant<key>::value);
+}
+#endif
 
 simdjson_inline void string_builder::append_raw(const char *c) noexcept {
   size_t len = std::strlen(c);
@@ -494,6 +508,7 @@ simdjson_inline void string_builder::append_raw(const char *str,
 #if SIMDJSON_SUPPORTS_CONCEPTS
 // Support for optional types (std::optional, etc.)
 template <concepts::optional_type T>
+  requires(!require_custom_serialization<T>)
 simdjson_inline void string_builder::append(const T &opt) {
   if (opt) {
     append(*opt);
@@ -501,18 +516,25 @@ simdjson_inline void string_builder::append(const T &opt) {
     append_null();
   }
 }
+
 template <typename T>
-requires(std::is_convertible<T, std::string_view>::value ||
-std::is_same<T, const char*>::value )
+  requires(require_custom_serialization<T>)
+simdjson_inline void string_builder::append(const T &val) {
+  serialize(*this, val);
+}
+
+template <typename T>
+  requires(std::is_convertible<T, std::string_view>::value ||
+           std::is_same<T, const char *>::value)
 simdjson_inline void string_builder::append(const T &value) {
   escape_and_append_with_quotes(value);
 }
 #endif
 
 #if SIMDJSON_SUPPORTS_RANGES && SIMDJSON_SUPPORTS_CONCEPTS
-  // Support for range-based appending (std::ranges::view, etc.)
+// Support for range-based appending (std::ranges::view, etc.)
 template <std::ranges::range R>
-requires (!std::is_convertible<R, std::string_view>::value)
+  requires(!std::is_convertible<R, std::string_view>::value)
 simdjson_inline void string_builder::append(const R &range) noexcept {
   auto it = std::ranges::begin(range);
   auto end = std::ranges::end(range);
@@ -529,8 +551,8 @@ simdjson_inline void string_builder::append(const R &range) noexcept {
 
     // Append remaining items with preceding commas
     for (; it != end; ++it) {
-        append_comma();
-        append_key_value(it->first, it->second);
+      append_comma();
+      append_key_value(it->first, it->second);
     }
     end_object();
   } else {
@@ -546,11 +568,10 @@ simdjson_inline void string_builder::append(const R &range) noexcept {
 
     // Append remaining items with preceding commas
     for (; it != end; ++it) {
-        append_comma();
-        append(*it);
+      append_comma();
+      append(*it);
     }
     end_array();
-
   }
 }
 
@@ -558,7 +579,7 @@ simdjson_inline void string_builder::append(const R &range) noexcept {
 
 #if SIMDJSON_EXCEPTIONS
 simdjson_inline string_builder::operator std::string() const noexcept(false) {
-  return std::string(std::string_view());
+  return std::string(operator std::string_view());
 }
 
 simdjson_inline string_builder::operator std::string_view() const
@@ -587,70 +608,95 @@ simdjson_inline bool string_builder::validate_unicode() const noexcept {
   return simdjson::validate_utf8(buffer.get(), position);
 }
 
-simdjson_inline void string_builder::start_object()  noexcept {
+simdjson_inline void string_builder::start_object() noexcept {
   if (capacity_check(1)) {
     buffer.get()[position++] = '{';
   }
 }
 
-
-simdjson_inline void string_builder::end_object()  noexcept {
+simdjson_inline void string_builder::end_object() noexcept {
   if (capacity_check(1)) {
     buffer.get()[position++] = '}';
   }
 }
 
-
-simdjson_inline void string_builder::start_array()  noexcept {
+simdjson_inline void string_builder::start_array() noexcept {
   if (capacity_check(1)) {
     buffer.get()[position++] = '[';
   }
 }
 
-
-simdjson_inline void string_builder::end_array()  noexcept {
+simdjson_inline void string_builder::end_array() noexcept {
   if (capacity_check(1)) {
     buffer.get()[position++] = ']';
   }
 }
 
-
-simdjson_inline void string_builder::append_comma()  noexcept {
+simdjson_inline void string_builder::append_comma() noexcept {
   if (capacity_check(1)) {
     buffer.get()[position++] = ',';
   }
 }
 
-
-simdjson_inline void string_builder::append_colon()  noexcept {
+simdjson_inline void string_builder::append_colon() noexcept {
   if (capacity_check(1)) {
     buffer.get()[position++] = ':';
   }
 }
 
-template<typename key_type, typename value_type>
-simdjson_inline void string_builder::append_key_value(key_type key, value_type value) noexcept {
-  static_assert(
-    std::is_same<key_type, const char*>::value ||
-    std::is_convertible<key_type, std::string_view>::value,
-    "Unsupported key type");
+template <typename key_type, typename value_type>
+simdjson_inline void
+string_builder::append_key_value(key_type key, value_type value) noexcept {
+  static_assert(std::is_same<key_type, const char *>::value ||
+                    std::is_convertible<key_type, std::string_view>::value,
+                "Unsupported key type");
   escape_and_append_with_quotes(key);
   append_colon();
   SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, std::nullptr_t>::value) {
     append_null();
-  } else SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, char>::value) {
+  }
+  else SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, char>::value) {
     escape_and_append_with_quotes(value);
-  } else SIMDJSON_IF_CONSTEXPR(std::is_convertible<value_type, std::string_view>::value) {
+  }
+  else SIMDJSON_IF_CONSTEXPR(
+      std::is_convertible<value_type, std::string_view>::value) {
     escape_and_append_with_quotes(value);
-  } else SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, const char*>::value) {
+  }
+  else SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, const char *>::value) {
     escape_and_append_with_quotes(value);
-  } else {
+  }
+  else {
     append(value);
   }
 }
 
+#if SIMDJSON_SUPPORTS_CONCEPTS
+template <constevalutil::fixed_string key, typename value_type>
+simdjson_inline void
+string_builder::append_key_value(value_type value) noexcept {
+  escape_and_append_with_quotes<key>();
+  append_colon();
+  SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, std::nullptr_t>::value) {
+    append_null();
+  }
+  else SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, char>::value) {
+    escape_and_append_with_quotes(value);
+  }
+  else SIMDJSON_IF_CONSTEXPR(
+      std::is_convertible<value_type, std::string_view>::value) {
+    escape_and_append_with_quotes(value);
+  }
+  else SIMDJSON_IF_CONSTEXPR(std::is_same<value_type, const char *>::value) {
+    escape_and_append_with_quotes(value);
+  }
+  else {
+    append(value);
+  }
+}
+#endif
+
 } // namespace builder
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#endif // SIMDJSON_GENERIC_STRING_BUILDER_INL_H
+#endif // SIMDJSON_GENERIC_STRING_BUILDER_INL_H

include/simdjson/generic/ondemand/json_string_builder.h

@@ -10,9 +10,40 @@
 #endif // SIMDJSON_CONDITIONAL_INCLUDE
 
 namespace simdjson {
+
+
+#if SIMDJSON_SUPPORTS_CONCEPTS
+
 namespace SIMDJSON_IMPLEMENTATION {
 namespace builder {
+  class string_builder;
+}}
 
+template <typename T, typename = void>
+struct has_custom_serialization : std::false_type {};
+
+inline constexpr struct serialize_tag {
+  template <typename T>
+    requires custom_deserializable<T>
+  constexpr void operator()(SIMDJSON_IMPLEMENTATION::builder::string_builder& b, T& obj) const{
+    return tag_invoke(*this, b, obj);
+  }
+
+
+} serialize{};
+template <typename T>
+struct has_custom_serialization<T, std::void_t<
+    decltype(tag_invoke(serialize, std::declval<SIMDJSON_IMPLEMENTATION::builder::string_builder&>(), std::declval<T&>()))
+>> : std::true_type {};
+
+template <typename T>
+constexpr bool require_custom_serialization = has_custom_serialization<T>::value;
+#else
+struct has_custom_serialization : std::false_type {};
+#endif // SIMDJSON_SUPPORTS_CONCEPTS
+
+namespace SIMDJSON_IMPLEMENTATION {
+namespace builder {
 /**
  * A builder for JSON strings representing documents. This is a low-level
  * builder that is not meant to be used directly by end-users. Though it
@@ -24,7 +55,9 @@ namespace builder {
  */
 class string_builder {
 public:
-  simdjson_inline string_builder(size_t initial_capacity = 1024);
+  simdjson_inline string_builder(size_t initial_capacity = DEFAULT_INITIAL_CAPACITY);
+
+  static constexpr size_t DEFAULT_INITIAL_CAPACITY = 1024;
 
   /**
    * Append number (includes Booleans). Booleans are mapped to the strings
@@ -33,7 +66,7 @@ public:
    * represents the number.
    */
   template<typename number_type,
-         typename = typename std::enable_if<std::is_arithmetic<number_type>::value>::type>
+    typename = typename std::enable_if<std::is_arithmetic<number_type>::value>::type>
   simdjson_inline void append(number_type v) noexcept;
 
   /**
@@ -62,7 +95,10 @@ public:
    * There is no UTF-8 validation.
    */
   simdjson_inline void escape_and_append_with_quotes(std::string_view input)  noexcept;
-
+#if SIMDJSON_SUPPORTS_CONCEPTS
+  template<constevalutil::fixed_string key>
+  simdjson_inline void escape_and_append_with_quotes()  noexcept;
+#endif
   /**
    * Append the character surrounded by double quotes, after escaping it.
    * There is no UTF-8 validation.
@@ -116,13 +152,21 @@ public:
    * The key is escaped and surrounded by double quotes.
    * The value is escaped if it is a string.
    */
-   template<typename key_type, typename value_type>
+  template<typename key_type, typename value_type>
   simdjson_inline void append_key_value(key_type key, value_type value) noexcept;
 #if SIMDJSON_SUPPORTS_CONCEPTS
+  template<constevalutil::fixed_string key, typename value_type>
+  simdjson_inline void append_key_value(value_type value) noexcept;
+
   // Support for optional types (std::optional, etc.)
   template <concepts::optional_type T>
+  requires(!require_custom_serialization<T>)
   simdjson_inline void append(const T &opt);
 
+  template <typename T>
+  requires(require_custom_serialization<T>)
+  simdjson_inline void append(const T &val);
+
   // Support for string-like types
   template <typename T>
   requires(std::is_convertible<T, std::string_view>::value ||
@@ -232,7 +276,7 @@ private:
 #if !SIMDJSON_STATIC_REFLECTION
 // fallback implementation until we have static reflection
 template <class Z>
-simdjson_result<std::string> to_json(const Z &z, size_t initial_capacity = 1024) {
+simdjson_warn_unused simdjson_result<std::string> to_json(const Z &z, size_t initial_capacity = simdjson::SIMDJSON_IMPLEMENTATION::builder::string_builder::DEFAULT_INITIAL_CAPACITY) {
   simdjson::SIMDJSON_IMPLEMENTATION::builder::string_builder b(initial_capacity);
   b.append(z);
   std::string_view s;
@@ -240,8 +284,20 @@ simdjson_result<std::string> to_json(const Z &z, size_t initial_capacity = 1024)
   if(e) { return e; }
   return std::string(s);
 }
+template <class Z>
+simdjson_warn_unused simdjson_error to_json(const Z &z, std::string &s, size_t initial_capacity = simdjson::SIMDJSON_IMPLEMENTATION::builder::string_builder::DEFAULT_INITIAL_CAPACITY) {
+  simdjson::SIMDJSON_IMPLEMENTATION::builder::string_builder b(initial_capacity);
+  b.append(z);
+  std::string_view sv;
+  auto e = b.view().get(sv);
+  if(e) { return e; }
+  s.assign(sv.data(), sv.size());
+  return simdjson::SUCCESS;
+}
 #endif
 
+#if SIMDJSON_SUPPORTS_CONCEPTS
+#endif // SIMDJSON_SUPPORTS_CONCEPTS
 
 } // namespace simdjson
 

include/simdjson/generic/ondemand/object-inl.h

@@ -9,6 +9,10 @@
 #include "simdjson/generic/ondemand/raw_json_string.h"
 #include "simdjson/generic/ondemand/json_iterator.h"
 #include "simdjson/generic/ondemand/value-inl.h"
+#if SIMDJSON_STATIC_REFLECTION
+#include "simdjson/generic/ondemand/json_string_builder.h"  // for constevalutil::fixed_string
+#include <meta>
+#endif
 #endif // SIMDJSON_CONDITIONAL_INCLUDE
 
 namespace simdjson {
@@ -66,7 +70,7 @@ simdjson_inline simdjson_result<object> object::start_root(value_iterator &iter)
   SIMDJSON_TRY( iter.start_root_object().error() );
   return object(iter);
 }
-simdjson_inline error_code object::consume() noexcept {
+simdjson_warn_unused simdjson_inline error_code object::consume() noexcept {
   if(iter.is_at_key()) {
     /**
      * whenever you are pointing at a key, calling skip_child() is
@@ -195,6 +199,52 @@ simdjson_inline simdjson_result<bool> object::reset() & noexcept {
   return iter.reset_object();
 }
 
+#if SIMDJSON_SUPPORTS_CONCEPTS && SIMDJSON_STATIC_REFLECTION
+
+template<constevalutil::fixed_string... FieldNames, typename T>
+  requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+simdjson_warn_unused simdjson_inline error_code object::extract_into(T& out) & noexcept {
+  // Helper to check if a field name matches any of the requested fields
+  auto should_extract = [](std::string_view field_name) constexpr -> bool {
+    return ((FieldNames.view() == field_name) || ...);
+  };
+
+  // Iterate through all members of T using reflection
+  template for (constexpr auto mem : std::define_static_array(
+      std::meta::nonstatic_data_members_of(^^T, std::meta::access_context::unchecked()))) {
+
+    if constexpr (!std::meta::is_const(mem) && std::meta::is_public(mem)) {
+      constexpr std::string_view key = std::define_static_string(std::meta::identifier_of(mem));
+
+      // Only extract this field if it's in our list of requested fields
+      if constexpr (should_extract(key)) {
+        // Try to find and extract the field
+        if constexpr (concepts::optional_type<decltype(out.[:mem:])>) {
+          // For optional fields, it's ok if they're missing
+          auto field_result = find_field_unordered(key);
+          if (!field_result.error()) {
+            auto error = field_result.get(out.[:mem:]);
+            if (error && error != NO_SUCH_FIELD) {
+              return error;
+            }
+          } else if (field_result.error() != NO_SUCH_FIELD) {
+            return field_result.error();
+          } else {
+            out.[:mem:].reset();
+          }
+        } else {
+          // For required fields (in the requested list), fail if missing
+          SIMDJSON_TRY((*this)[key].get(out.[:mem:]));
+        }
+      }
+    }
+  };
+
+  return SUCCESS;
+}
+
+#endif // SIMDJSON_SUPPORTS_CONCEPTS && SIMDJSON_STATIC_REFLECTION
+
 } // namespace ondemand
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson

include/simdjson/generic/ondemand/object.h

@@ -5,6 +5,9 @@
 #include "simdjson/generic/ondemand/base.h"
 #include "simdjson/generic/implementation_simdjson_result_base.h"
 #include "simdjson/generic/ondemand/value_iterator.h"
+#if SIMDJSON_STATIC_REFLECTION && SIMDJSON_SUPPORTS_CONCEPTS
+#include "simdjson/generic/ondemand/json_string_builder.h"  // for constevalutil::fixed_string
+#endif
 #endif // SIMDJSON_CONDITIONAL_INCLUDE
 
 namespace simdjson {
@@ -211,7 +214,7 @@ public:
    * @returns SUCCESS If the parse succeeded and the out parameter was set to the value.
    */
   template <typename T>
-  simdjson_inline error_code get(T &out)
+  simdjson_warn_unused simdjson_inline error_code get(T &out)
      noexcept(custom_deserializable<T, object> ? nothrow_custom_deserializable<T, object> : true) {
     static_assert(custom_deserializable<T, object>);
     return deserialize(*this, out);
@@ -231,12 +234,42 @@ public:
     SIMDJSON_TRY(get<T>(out));
     return out;
   }
+
+#if SIMDJSON_STATIC_REFLECTION
+  /**
+   * Extract only specific fields from the JSON object into a struct.
+   *
+   * This allows selective deserialization of only the fields you need,
+   * potentially improving performance by skipping unwanted fields.
+   *
+   * Example:
+   * ```c++
+   * struct Car {
+   *   std::string make;
+   *   std::string model;
+   *   int year;
+   *   double price;
+   * };
+   *
+   * Car car;
+   * object.extract_into<"make", "model">(car);
+   * // Only 'make' and 'model' fields are extracted from JSON
+   * ```
+   *
+   * @tparam FieldNames Compile-time string literals specifying which fields to extract
+   * @param out The output struct to populate with selected fields
+   * @returns SUCCESS on success, or an error code if a required field is missing or has wrong type
+   */
+  template<constevalutil::fixed_string... FieldNames, typename T>
+    requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+  simdjson_warn_unused simdjson_inline error_code extract_into(T& out) & noexcept;
+#endif // SIMDJSON_STATIC_REFLECTION
 #endif // SIMDJSON_SUPPORTS_CONCEPTS
 protected:
   /**
    * Go to the end of the object, no matter where you are right now.
    */
-  simdjson_inline error_code consume() noexcept;
+  simdjson_warn_unused simdjson_inline error_code consume() noexcept;
   static simdjson_inline simdjson_result<object> start(value_iterator &iter) noexcept;
   static simdjson_inline simdjson_result<object> start_root(value_iterator &iter) noexcept;
   static simdjson_inline simdjson_result<object> started(value_iterator &iter) noexcept;
@@ -291,7 +324,7 @@ public:
     return first.get<T>();
   }
   template<typename T>
-  simdjson_inline error_code get(T& out) noexcept {
+  simdjson_warn_unused simdjson_inline error_code get(T& out) noexcept {
     if (error()) { return error(); }
     if constexpr (std::is_same_v<T, SIMDJSON_IMPLEMENTATION::ondemand::object>) {
       out = first;
@@ -300,6 +333,16 @@ public:
     }
     return SUCCESS;
   }
+
+#if SIMDJSON_STATIC_REFLECTION
+  // TODO: move this code into object-inl.h
+  template<constevalutil::fixed_string... FieldNames, typename T>
+    requires(std::is_class_v<T> && (sizeof...(FieldNames) > 0))
+  simdjson_warn_unused simdjson_inline error_code extract_into(T& out) noexcept {
+    if (error()) { return error(); }
+    return first.extract_into<FieldNames...>(out);
+  }
+#endif // SIMDJSON_STATIC_REFLECTION
 #endif // SIMDJSON_SUPPORTS_CONCEPTS
 };
 

include/simdjson/generic/ondemand/std_deserialize.h

@@ -16,15 +16,12 @@
 #endif
 
 namespace simdjson {
-template <typename T>
-constexpr bool require_custom_serialization = false;
 
 //////////////////////////////
 // Number deserialization
 //////////////////////////////
 
 template <std::unsigned_integral T>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept {
   using limits = std::numeric_limits<T>;
 
@@ -38,7 +35,6 @@ error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept {
 }
 
 template <std::floating_point T>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept {
   double x;
   SIMDJSON_TRY(val.get_double().get(x));
@@ -47,7 +43,6 @@ error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept {
 }
 
 template <std::signed_integral T>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept {
   using limits = std::numeric_limits<T>;
 
@@ -77,7 +72,6 @@ error_code tag_invoke(deserialize_tag, auto &val, char &out) noexcept {
 
 // any string-like type (can be constructed from std::string_view)
 template <concepts::constructible_from_string_view T, typename ValT>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(std::is_nothrow_constructible_v<T, std::string_view>) {
   std::string_view str;
   SIMDJSON_TRY(val.get_string().get(str));
@@ -94,7 +88,6 @@ error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(std::is_nothr
  * doc.get<std::vector<int>>().
  */
 template <concepts::appendable_containers T, typename ValT>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(false) {
   using value_type = typename std::remove_cvref_t<T>::value_type;
   static_assert(
@@ -140,7 +133,6 @@ error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(false) {
  * string-keyed types.
  */
  template <concepts::string_view_keyed_map T, typename ValT>
- requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(false) {
   using value_type = typename std::remove_cvref_t<T>::mapped_type;
   static_assert(
@@ -222,7 +214,6 @@ error_code tag_invoke(deserialize_tag, SIMDJSON_IMPLEMENTATION::ondemand::docume
  * @return status of the conversion
  */
 template <concepts::smart_pointer T, typename ValT>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(nothrow_deserializable<typename std::remove_cvref_t<T>::element_type, ValT>) {
   using element_type = typename std::remove_cvref_t<T>::element_type;
 
@@ -248,12 +239,13 @@ error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept(nothrow_deser
  * This CPO (Customization Point Object) will help deserialize into optional types.
  */
 template <concepts::optional_type T>
-  requires(!require_custom_serialization<T>)
 error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept(nothrow_deserializable<typename std::remove_cvref_t<T>::value_type, decltype(val)>) {
   using value_type = typename std::remove_cvref_t<T>::value_type;
 
   // Check if the value is null
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset(); // Set to nullopt
     return SUCCESS;
   }
@@ -272,7 +264,7 @@ error_code tag_invoke(deserialize_tag, auto &val, T &out) noexcept(nothrow_deser
 template <typename T>
 constexpr bool user_defined_type = (std::is_class_v<T>
 && !std::is_same_v<T, std::string> && !std::is_same_v<T, std::string_view> && !concepts::optional_type<T> &&
-!concepts::appendable_containers<T> && !require_custom_serialization<T>);
+!concepts::appendable_containers<T>);
 
 
 template <typename T, typename ValT>
@@ -284,18 +276,26 @@ error_code tag_invoke(deserialize_tag, ValT &val, T &out) noexcept {
   } else {
     SIMDJSON_TRY(val.get_object().get(obj));
   }
-  error_code e = simdjson::SUCCESS;
   template for (constexpr auto mem : std::define_static_array(std::meta::nonstatic_data_members_of(^^T, std::meta::access_context::unchecked()))) {
-        if constexpr (!std::meta::is_const(mem) && std::meta::is_public(mem)) {
+    if constexpr (!std::meta::is_const(mem) && std::meta::is_public(mem)) {
       constexpr std::string_view key = std::define_static_string(std::meta::identifier_of(mem));
-      // Note: removed static assert as optional types are now handled generically
-      // as long we are succesful or the field is not found, we continue
-      if(e == simdjson::SUCCESS || e == simdjson::NO_SUCH_FIELD) {
-        e = obj[key].get(out.[:mem:]);
+      if constexpr (concepts::optional_type<decltype(out.[:mem:])>) {
+        // for optional members, it's ok if the key is missing
+        auto error = obj[key].get(out.[:mem:]);
+        if (error && error != NO_SUCH_FIELD) {
+          if(error == NO_SUCH_FIELD) {
+            out.[:mem:].reset();
+            continue;
+          }
+          return error;
+        }
+      } else {
+        // for non-optional members, the key must be present
+        SIMDJSON_TRY(obj[key].get(out.[:mem:]));
       }
     }
   };
-  return e;
+  return simdjson::SUCCESS;
 }
 
 // Support for enum deserialization - deserialize from string representation using expand approach from P2996R12
@@ -361,7 +361,9 @@ error_code tag_invoke(deserialize_tag, simdjson_value &val, std::shared_ptr<T> &
 // Unique pointers
 ////////////////////////////////////////
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<bool> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -374,7 +376,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<bool> &out) no
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<int64_t> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -387,7 +391,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<int64_t> &out)
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<uint64_t> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -400,7 +406,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<uint64_t> &out
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<double> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -413,7 +421,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<double> &out)
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<std::string_view> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -430,7 +440,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<std::string_vi
 // Shared pointers
 ////////////////////////////////////////
 error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<bool> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -443,7 +455,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<bool> &out) no
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<int64_t> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -456,7 +470,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<int64_t> &out)
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<uint64_t> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -469,7 +485,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<uint64_t> &out
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<double> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -482,7 +500,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<double> &out)
 }
 
 error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<std::string_view> &out) noexcept {
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset();
     return SUCCESS;
   }
@@ -504,7 +524,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<std::string_vi
 ////////////////////////////////////////
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<std::string> &out) noexcept {
   // Check if the value is null
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset(); // Set to nullptr
     return SUCCESS;
   }
@@ -520,7 +542,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<std::string> &
 
 error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<std::string> &out) noexcept {
   // Check if the value is null
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset(); // Set to nullptr
     return SUCCESS;
   }
@@ -536,7 +560,9 @@ error_code tag_invoke(deserialize_tag, auto &val, std::shared_ptr<std::string> &
 
 error_code tag_invoke(deserialize_tag, auto &val, std::unique_ptr<int> &out) noexcept {
   // Check if the value is null
-  if (val.is_null()) {
+  bool is_null_value;
+  SIMDJSON_TRY( val.is_null().get(is_null_value) );
+  if (is_null_value) {
     out.reset(); // Set to nullptr
     return SUCCESS;
   }

include/simdjson/generic/ondemand/value-inl.h

@@ -48,7 +48,7 @@ simdjson_inline simdjson_result<std::string_view> value::get_string(bool allow_r
   return iter.get_string(allow_replacement);
 }
 template <typename string_type>
-simdjson_inline error_code value::get_string(string_type& receiver, bool allow_replacement) noexcept {
+simdjson_warn_unused simdjson_inline error_code value::get_string(string_type& receiver, bool allow_replacement) noexcept {
   return iter.get_string(receiver, allow_replacement);
 }
 simdjson_inline simdjson_result<std::string_view> value::get_wobbly_string() noexcept {
@@ -90,15 +90,15 @@ template<> simdjson_inline simdjson_result<int64_t> value::get() noexcept { retu
 template<> simdjson_inline simdjson_result<bool> value::get() noexcept { return get_bool(); }
 
 
-template<> simdjson_inline error_code value::get(array& out) noexcept { return get_array().get(out); }
-template<> simdjson_inline error_code value::get(object& out) noexcept { return get_object().get(out); }
-template<> simdjson_inline error_code value::get(raw_json_string& out) noexcept { return get_raw_json_string().get(out); }
-template<> simdjson_inline error_code value::get(std::string_view& out) noexcept { return get_string(false).get(out); }
-template<> simdjson_inline error_code value::get(number& out) noexcept { return get_number().get(out); }
-template<> simdjson_inline error_code value::get(double& out) noexcept { return get_double().get(out); }
-template<> simdjson_inline error_code value::get(uint64_t& out) noexcept { return get_uint64().get(out); }
-template<> simdjson_inline error_code value::get(int64_t& out) noexcept { return get_int64().get(out); }
-template<> simdjson_inline error_code value::get(bool& out) noexcept { return get_bool().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(array& out) noexcept { return get_array().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(object& out) noexcept { return get_object().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(raw_json_string& out) noexcept { return get_raw_json_string().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(std::string_view& out) noexcept { return get_string(false).get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(number& out) noexcept { return get_number().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(double& out) noexcept { return get_double().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(uint64_t& out) noexcept { return get_uint64().get(out); }
+template<> simdjson_warn_unused simdjson_inline error_code value::get(int64_t& out) noexcept { return get_int64().get(out); }
+template<>  simdjson_warn_unused simdjson_inline error_code value::get(bool& out) noexcept { return get_bool().get(out); }
 
 #if SIMDJSON_EXCEPTIONS
 template <class T>

include/simdjson/generic/ondemand/value.h

@@ -65,7 +65,7 @@ public:
    * @returns SUCCESS If the parse succeeded and the out parameter was set to the value.
    */
   template <typename T>
-  simdjson_inline error_code get(T &out)
+  simdjson_warn_unused simdjson_inline error_code get(T &out)
 #if SIMDJSON_SUPPORTS_CONCEPTS
     noexcept(custom_deserializable<T, value> ? nothrow_custom_deserializable<T, value> : true)
 #else
@@ -79,7 +79,9 @@ public:
       using value_type = typename std::remove_cvref_t<T>::value_type;
 
       // Check if the value is null
-      if (is_null()) {
+      bool is_null_value;
+      SIMDJSON_TRY( is_null().get(is_null_value) );
+      if (is_null_value) {
         out.reset(); // Set to nullopt
         return SUCCESS;
       }
@@ -215,7 +217,7 @@ public:
    * @returns INCORRECT_TYPE if the JSON value is not a string. Otherwise, we return SUCCESS.
    */
   template <typename string_type>
-  simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
+  simdjson_warn_unused simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
 
   /**
    * Cast this JSON value to a "wobbly" string.
@@ -736,7 +738,7 @@ public:
   simdjson_inline simdjson_result<double> get_double_in_string() noexcept;
   simdjson_inline simdjson_result<std::string_view> get_string(bool allow_replacement = false) noexcept;
   template <typename string_type>
-  simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
+  simdjson_warn_unused simdjson_inline error_code get_string(string_type& receiver, bool allow_replacement = false) noexcept;
   simdjson_inline simdjson_result<std::string_view> get_wobbly_string() noexcept;
   simdjson_inline simdjson_result<SIMDJSON_IMPLEMENTATION::ondemand::raw_json_string> get_raw_json_string() noexcept;
   simdjson_inline simdjson_result<bool> get_bool() noexcept;

include/simdjson/generic/ondemand/value_iterator-inl.h

@@ -41,7 +41,7 @@ simdjson_warn_unused simdjson_inline simdjson_result<bool> value_iterator::start
   if (*_json_iter->peek() == '}') {
     logger::log_value(*_json_iter, "empty object");
     _json_iter->return_current_and_advance();
-    end_container();
+    SIMDJSON_TRY(end_container());
     return false;
   }
   return true;
@@ -895,7 +895,7 @@ simdjson_inline void value_iterator::advance_scalar(const char *type) noexcept {
   _json_iter->ascend_to(depth()-1);
 }
 
-simdjson_inline error_code value_iterator::start_container(uint8_t start_char, const char *incorrect_type_message, const char *type) noexcept {
+simdjson_warn_unused simdjson_inline error_code value_iterator::start_container(uint8_t start_char, const char *incorrect_type_message, const char *type) noexcept {
   logger::log_start_value(*_json_iter, start_position(), depth(), type);
   // If we're not at the position anymore, we don't want to advance the cursor.
   const uint8_t *json;

include/simdjson/generic/ondemand/value_iterator.h

@@ -335,7 +335,7 @@ public:
   simdjson_warn_unused simdjson_inline simdjson_result<number> get_root_number(bool check_trailing) noexcept;
   simdjson_warn_unused simdjson_inline simdjson_result<bool> is_root_null(bool check_trailing) noexcept;
 
-  simdjson_inline error_code error() const noexcept;
+  simdjson_warn_unused simdjson_inline error_code error() const noexcept;
   simdjson_inline uint8_t *&string_buf_loc() noexcept;
   simdjson_inline const json_iterator &json_iter() const noexcept;
   simdjson_inline json_iterator &json_iter() noexcept;
@@ -419,8 +419,8 @@ protected:
   simdjson_inline const uint8_t *peek_non_root_scalar(const char *type) noexcept;
 
 
-  simdjson_inline error_code start_container(uint8_t start_char, const char *incorrect_type_message, const char *type) noexcept;
-  simdjson_inline error_code end_container() noexcept;
+  simdjson_warn_unused simdjson_inline error_code start_container(uint8_t start_char, const char *incorrect_type_message, const char *type) noexcept;
+  simdjson_warn_unused simdjson_inline error_code end_container() noexcept;
 
   /**
    * Advance to a place expecting a value (increasing depth).
@@ -430,8 +430,8 @@ protected:
    */
   simdjson_inline simdjson_result<const uint8_t *> advance_to_value() noexcept;
 
-  simdjson_inline error_code incorrect_type_error(const char *message) const noexcept;
-  simdjson_inline error_code error_unless_more_tokens(uint32_t tokens=1) const noexcept;
+  simdjson_warn_unused simdjson_inline error_code incorrect_type_error(const char *message) const noexcept;
+  simdjson_warn_unused simdjson_inline error_code error_unless_more_tokens(uint32_t tokens=1) const noexcept;
 
   simdjson_inline bool is_at_start() const noexcept;
   /**
@@ -468,7 +468,7 @@ protected:
   /** @copydoc error_code json_iterator::end_position() const noexcept; */
   simdjson_inline token_position end_position() const noexcept;
   /** @copydoc error_code json_iterator::report_error(error_code error, const char *message) noexcept; */
-  simdjson_inline error_code report_error(error_code error, const char *message) noexcept;
+  simdjson_warn_unused simdjson_inline error_code report_error(error_code error, const char *message) noexcept;
 
   friend class document;
   friend class object;

include/simdjson/haswell/stringparsing_defs.h

@@ -17,7 +17,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 32;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return ((bs_bits - 1) & quote_bits) != 0; }
   simdjson_inline bool has_backslash() { return ((quote_bits - 1) & bs_bits) != 0; }

include/simdjson/icelake/stringparsing_defs.h

@@ -17,7 +17,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 64;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return ((bs_bits - 1) & quote_bits) != 0; }
   simdjson_inline bool has_backslash() { return ((quote_bits - 1) & bs_bits) != 0; }

include/simdjson/lasx/stringparsing_defs.h

@@ -17,7 +17,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 32;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return ((bs_bits - 1) & quote_bits) != 0; }
   simdjson_inline bool has_backslash() { return bs_bits != 0; }

include/simdjson/lsx/stringparsing_defs.h

@@ -17,7 +17,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 32;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return ((bs_bits - 1) & quote_bits) != 0; }
   simdjson_inline bool has_backslash() { return bs_bits != 0; }
@@ -67,7 +67,7 @@ simdjson_inline escaping escaping::copy_and_find(const uint8_t *src, uint8_t *ds
   simd8<bool> is_backslash = (v == '\\');
   simd8<bool> is_control = (v < 32);
   return {
-    (is_backslash | is_quote | is_control).to_bitmask()
+    static_cast<uint64_t>((is_backslash | is_quote | is_control).to_bitmask())
   };
 }
 

include/simdjson/ppc64/stringparsing_defs.h

@@ -17,7 +17,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 32;
-  simdjson_inline static backslash_and_quote
+  simdjson_inline backslash_and_quote
   copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() {

include/simdjson/simdjson_version.h

@@ -4,7 +4,7 @@
 #define SIMDJSON_SIMDJSON_VERSION_H
 
 /** The version of simdjson being used (major.minor.revision) */
-#define SIMDJSON_VERSION "4.0.0"
+#define SIMDJSON_VERSION "4.0.7"
 
 namespace simdjson {
 enum {
@@ -19,7 +19,7 @@ enum {
   /**
    * The revision (major.minor.REVISION) of simdjson being used.
    */
-  SIMDJSON_VERSION_REVISION = 0
+  SIMDJSON_VERSION_REVISION = 7
 };
 } // namespace simdjson
 

include/simdjson/westmere/stringparsing_defs.h

@@ -14,7 +14,7 @@ using namespace simd;
 struct backslash_and_quote {
 public:
   static constexpr uint32_t BYTES_PROCESSED = 32;
-  simdjson_inline static backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
+  simdjson_inline backslash_and_quote copy_and_find(const uint8_t *src, uint8_t *dst);
 
   simdjson_inline bool has_quote_first() { return ((bs_bits - 1) & quote_bits) != 0; }
   simdjson_inline bool has_backslash() { return bs_bits != 0; }

src/fallback.cpp

@@ -209,7 +209,7 @@ simdjson_inline bool validate_string() {
 //
 // Parse the entire input in STEP_SIZE-byte chunks.
 //
-simdjson_inline error_code scan() {
+simdjson_warn_unused simdjson_inline error_code scan() {
   bool unclosed_string = false;
   for (;idx<len;idx++) {
     do {

src/generic/stage1/json_minifier.h

@@ -29,7 +29,7 @@ private:
   template<size_t STEP_SIZE>
   simdjson_inline void step(const uint8_t *block_buf, buf_block_reader<STEP_SIZE> &reader) noexcept;
   simdjson_inline void next(const simd::simd8x64<uint8_t>& in, const json_block& block);
-  simdjson_inline error_code finish(uint8_t *dst_start, size_t &dst_len);
+  simdjson_warn_unused simdjson_inline error_code finish(uint8_t *dst_start, size_t &dst_len);
   json_scanner scanner{};
   uint8_t *dst;
 };
@@ -39,7 +39,7 @@ simdjson_inline void json_minifier::next(const simd::simd8x64<uint8_t>& in, cons
   dst += in.compress(mask, dst);
 }
 
-simdjson_inline error_code json_minifier::finish(uint8_t *dst_start, size_t &dst_len) {
+simdjson_warn_unused simdjson_inline error_code json_minifier::finish(uint8_t *dst_start, size_t &dst_len) {
   error_code error = scanner.finish();
   if (error) { dst_len = 0; return error; }
   dst_len = dst - dst_start;

src/generic/stage1/json_scanner.h

@@ -108,7 +108,7 @@ public:
   json_scanner() = default;
   simdjson_inline json_block next(const simd::simd8x64<uint8_t>& in);
   // Returns either UNCLOSED_STRING or SUCCESS
-  simdjson_inline error_code finish();
+  simdjson_warn_unused simdjson_inline error_code finish();
 
 private:
   // Whether the last character of the previous iteration is part of a scalar token
@@ -156,7 +156,7 @@ simdjson_inline json_block json_scanner::next(const simd::simd8x64<uint8_t>& in)
   );
 }
 
-simdjson_inline error_code json_scanner::finish() {
+simdjson_warn_unused simdjson_inline error_code json_scanner::finish() {
   return string_scanner.finish();
 }
 

src/generic/stage1/json_structural_indexer.h

@@ -141,7 +141,7 @@ private:
   template<size_t STEP_SIZE>
   simdjson_inline void step(const uint8_t *block, buf_block_reader<STEP_SIZE> &reader) noexcept;
   simdjson_inline void next(const simd::simd8x64<uint8_t>& in, const json_block& block, size_t idx);
-  simdjson_inline error_code finish(dom_parser_implementation &parser, size_t idx, size_t len, stage1_mode partial);
+  simdjson_warn_unused simdjson_inline error_code finish(dom_parser_implementation &parser, size_t idx, size_t len, stage1_mode partial);
 
   json_scanner scanner{};
   utf8_checker checker{};

src/generic/stage1/utf8_lookup4_algorithm.h

@@ -195,7 +195,7 @@ using namespace simd;
       }
     }
     // do not forget to call check_eof!
-    simdjson_inline error_code errors() {
+    simdjson_warn_unused simdjson_inline error_code errors() {
       return this->error.any_bits_set_anywhere() ? error_code::UTF8_ERROR : error_code::SUCCESS;
     }
 

src/generic/stage2/stringparsing.h

@@ -151,7 +151,8 @@ simdjson_inline bool handle_unicode_codepoint_wobbly(const uint8_t **src_ptr,
 simdjson_warn_unused simdjson_inline uint8_t *parse_string(const uint8_t *src, uint8_t *dst, bool allow_replacement) {
   while (1) {
     // Copy the next n bytes, and find the backslash and quote in them.
-    auto bs_quote = backslash_and_quote::copy_and_find(src, dst);
+    auto b = backslash_and_quote{};
+    auto bs_quote = b.copy_and_find(src, dst);
     // If the next thing is the end quote, copy and return
     if (bs_quote.has_quote_first()) {
       // we encountered quotes first. Move dst to point to quotes and exit
@@ -196,7 +197,8 @@ simdjson_warn_unused simdjson_inline uint8_t *parse_wobbly_string(const uint8_t
   // It is not ideal that this function is nearly identical to parse_string.
   while (1) {
     // Copy the next n bytes, and find the backslash and quote in them.
-    auto bs_quote = backslash_and_quote::copy_and_find(src, dst);
+    auto b = backslash_and_quote{};
+    auto bs_quote = b.copy_and_find(src, dst);
     // If the next thing is the end quote, copy and return
     if (bs_quote.has_quote_first()) {
       // we encountered quotes first. Move dst to point to quotes and exit

tests/builder/CMakeLists.txt

@@ -1,7 +1,8 @@
 # All remaining tests link with simdjson proper
 include_directories(..)
-add_cpp_test(builder_string_builder_tests              LABELS ondemand acceptance per_implementation)
+add_cpp_test(builder_string_builder_tests                LABELS ondemand acceptance per_implementation)
 if(SIMDJSON_STATIC_REFLECTION)
+  add_cpp_test(static_reflection_custom_tests            LABELS ondemand acceptance per_implementation)
   add_cpp_test(static_reflection_builder_tests           LABELS ondemand acceptance per_implementation)
   add_cpp_test(static_reflection_comprehensive_tests     LABELS ondemand acceptance per_implementation)
   add_cpp_test(static_reflection_edge_cases_tests        LABELS ondemand acceptance per_implementation)

tests/builder/static_reflection_builder_tests.cpp

@@ -50,9 +50,8 @@ namespace builder_tests {
     TEST_START();
 #if SIMDJSON_STATIC_REFLECTION
     Car c = {"Toyota", "Corolla", 2017, {30.0,30.2,30.513,30.79}};
-    auto result = builder::to_json_string(c);
-    ASSERT_SUCCESS(result);
-    std::string pstr = result.value();
+    std::string pstr;
+    ASSERT_SUCCESS(builder::to_json_string(c).get(pstr));
     ASSERT_EQUAL(pstr, "{\"make\":\"Toyota\",\"model\":\"Corolla\",\"year\":2017,\"tire_pressure\":[30.0,30.2,30.513,30.79]}");
     simdjson::ondemand::parser parser;
     simdjson::ondemand::document doc;

tests/builder/static_reflection_comprehensive_tests.cpp

@@ -3,6 +3,7 @@
 #include <string>
 #include <string_view>
 #include <vector>
+#include <list>
 #include <set>
 #include <map>
 #include <optional>
@@ -12,6 +13,84 @@ using namespace simdjson;
 
 namespace builder_tests {
 
+#if SIMDJSON_STATIC_REFLECTION
+  // Custom type for testing tag_invoke with extract_into
+  struct Price {
+    double amount;
+    std::string currency;
+
+    // Custom deserializer that applies currency conversion
+    friend error_code tag_invoke(deserialize_tag,
+                                ondemand::value& val,
+                                Price& price) noexcept {
+      ondemand::object obj;
+      auto error = val.get_object().get(obj);
+      if (error) return error;
+
+      // Get the raw amount
+      error = obj["amount"].get(price.amount);
+      if (error) return error;
+
+      // Get the currency
+      std::string_view currency_sv;
+      error = obj["currency"].get(currency_sv);
+      if (error) return error;
+      price.currency = std::string(currency_sv);
+
+      // Custom logic: Convert EUR to USD for consistency
+      if (price.currency == "EUR") {
+        price.amount = price.amount * 1.1;  // Simplified conversion
+        price.currency = "USD";
+      }
+
+      return SUCCESS;
+    }
+  };
+
+  struct Product {
+    std::string name;
+    Price price;  // Custom deserializable type
+    int stock;
+  };
+
+  // Another custom type for testing
+  struct Dimensions {
+    double value;
+    std::string unit;
+
+    // Custom deserializer that converts to metric
+    friend error_code tag_invoke(deserialize_tag,
+                                ondemand::value& val,
+                                Dimensions& dim) noexcept {
+      ondemand::object obj;
+      auto error = val.get_object().get(obj);
+      if (error) return error;
+
+      error = obj["value"].get(dim.value);
+      if (error) return error;
+
+      std::string_view unit_sv;
+      error = obj["unit"].get(unit_sv);
+      if (error) return error;
+      dim.unit = std::string(unit_sv);
+
+      // Convert inches to cm
+      if (dim.unit == "inches") {
+        dim.value = dim.value * 2.54;
+        dim.unit = "cm";
+      }
+
+      return SUCCESS;
+    }
+  };
+
+  struct Package {
+    std::string id;
+    Dimensions weight;
+    Dimensions length;
+  };
+#endif
+
   bool test_primitive_types() {
     TEST_START();
 #if SIMDJSON_STATIC_REFLECTION
@@ -25,10 +104,9 @@ namespace builder_tests {
 
     PrimitiveTypes test{true, 'X', 42, 3.14159, 2.71f};
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
 
-    std::string json = result.value();
     ASSERT_TRUE(json.find("\"bool_val\":true") != std::string::npos);
     ASSERT_TRUE(json.find("\"char_val\":\"X\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"int_val\":42") != std::string::npos);
@@ -39,10 +117,9 @@ namespace builder_tests {
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
 
-    auto get_result = doc_result.value().get<PrimitiveTypes>();
-    ASSERT_SUCCESS(get_result);
+    PrimitiveTypes deserialized;
+    ASSERT_SUCCESS(doc_result.get<PrimitiveTypes>().get(deserialized));
 
-    PrimitiveTypes deserialized = std::move(get_result.value());
     ASSERT_EQUAL(deserialized.bool_val, test.bool_val);
     ASSERT_EQUAL(deserialized.char_val, test.char_val);
     ASSERT_EQUAL(deserialized.int_val, test.int_val);
@@ -60,11 +137,9 @@ namespace builder_tests {
     };
 
     StringTypes test{"hello world", "test_view"};
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
     ASSERT_TRUE(json.find("\"string_val\":\"hello world\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"string_view_val\":\"test_view\"") != std::string::npos);
 
@@ -72,11 +147,9 @@ namespace builder_tests {
     ondemand::parser parser;
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
+    StringTypes deserialized;
+    ASSERT_SUCCESS(doc_result.get<StringTypes>().get(deserialized));
 
-    auto get_result = doc_result.value().get<StringTypes>();
-    ASSERT_SUCCESS(get_result);
-
-    StringTypes deserialized = std::move(get_result.value());
     ASSERT_EQUAL(deserialized.string_val, test.string_val);
 #endif
     TEST_SUCCEED();
@@ -98,10 +171,8 @@ namespace builder_tests {
     test.opt_int_null = std::nullopt;
     test.opt_string_null = std::nullopt;
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"opt_int_with_value\":42") != std::string::npos);
     ASSERT_TRUE(json.find("\"opt_string_with_value\":\"optional_test\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"opt_int_null\":null") != std::string::npos);
@@ -112,10 +183,9 @@ namespace builder_tests {
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
 
-    auto get_result = doc_result.value().get<OptionalTypes>();
-    ASSERT_SUCCESS(get_result);
+    OptionalTypes deserialized;
+    ASSERT_SUCCESS(doc_result.get<OptionalTypes>().get(deserialized));
 
-    OptionalTypes deserialized = std::move(get_result.value());
     ASSERT_TRUE(deserialized.opt_int_with_value.has_value());
     ASSERT_EQUAL(*deserialized.opt_int_with_value, 42);
     ASSERT_TRUE(deserialized.opt_string_with_value.has_value());
@@ -144,10 +214,8 @@ namespace builder_tests {
     test.unique_int_null = nullptr;
     test.shared_string_null = nullptr;
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"unique_int_with_value\":123") != std::string::npos);
     ASSERT_TRUE(json.find("\"shared_string_with_value\":\"shared_test\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"unique_bool_with_value\":true") != std::string::npos);
@@ -157,12 +225,9 @@ namespace builder_tests {
     // Test round-trip
     ondemand::parser parser;
     auto doc_result = parser.iterate(pad(json));
-    ASSERT_SUCCESS(doc_result);
 
-    auto get_result = doc_result.value().get<SmartPointerTypes>();
-    ASSERT_SUCCESS(get_result);
-
-    SmartPointerTypes deserialized = std::move(get_result.value());
+    SmartPointerTypes deserialized;
+    ASSERT_SUCCESS(doc_result.get<SmartPointerTypes>().get(deserialized));
     ASSERT_TRUE(deserialized.unique_int_with_value != nullptr);
     ASSERT_EQUAL(*deserialized.unique_int_with_value, 123);
     ASSERT_TRUE(deserialized.shared_string_with_value != nullptr);
@@ -178,6 +243,7 @@ namespace builder_tests {
   bool test_container_types() {
     TEST_START();
 #if SIMDJSON_STATIC_REFLECTION
+    // Test basic container types
     struct ContainerTypes {
       std::vector<int> int_vector;
       std::set<std::string> string_set;
@@ -192,7 +258,8 @@ namespace builder_tests {
     auto result = builder::to_json_string(test);
     ASSERT_SUCCESS(result);
 
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"int_vector\":[1,2,3,4,5]") != std::string::npos);
     ASSERT_TRUE(json.find("\"string_set\":[") != std::string::npos);
     ASSERT_TRUE(json.find("\"string_map\":{") != std::string::npos);
@@ -201,27 +268,447 @@ namespace builder_tests {
     ondemand::parser parser;
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
-
-    auto get_result = doc_result.value().get<ContainerTypes>();
-    ASSERT_SUCCESS(get_result);
-
-    ContainerTypes deserialized = std::move(get_result.value());
+    ContainerTypes deserialized;
+    ASSERT_SUCCESS(doc_result.get<ContainerTypes>().get(deserialized));
     ASSERT_EQUAL(deserialized.int_vector.size(), 5);
     ASSERT_EQUAL(deserialized.string_set.size(), 3);
     ASSERT_EQUAL(deserialized.string_map.size(), 3);
     ASSERT_EQUAL(deserialized.int_vector[0], 1);
     ASSERT_EQUAL(deserialized.int_vector[4], 5);
+
+    // Test std::list with iterator-based serialization
+    struct ListContainer {
+      std::list<int> int_list;
+      std::list<std::string> string_list;
+    };
+
+    ListContainer list_test;
+    list_test.int_list = {10, 20, 30, 40, 50};
+    list_test.string_list = {"first", "second", "third"};
+
+    std::string list_result;
+    ASSERT_SUCCESS( builder::to_json_string(list_test).get(list_result));
+
+    // Check that list serialization produces correct JSON array format
+    ASSERT_TRUE(list_result.find("\"int_list\":[10,20,30,40,50]") != std::string::npos);
+    ASSERT_TRUE(list_result.find("\"string_list\":[\"first\",\"second\",\"third\"]") != std::string::npos);
+
+    // Test list round-trip
+    auto list_doc_result = parser.iterate(pad(list_result));
+    ASSERT_SUCCESS(list_doc_result);
+
+    ListContainer list_deserialized;
+    ASSERT_SUCCESS(list_doc_result.get<ListContainer>().get(list_deserialized));
+    ASSERT_EQUAL(list_deserialized.int_list.size(), 5);
+    ASSERT_EQUAL(list_deserialized.string_list.size(), 3);
+
+    // Check list values
+    auto it = list_deserialized.int_list.begin();
+    ASSERT_EQUAL(*it, 10);
+    std::advance(it, 4);
+    ASSERT_EQUAL(*it, 50);
+
+    auto str_it = list_deserialized.string_list.begin();
+    ASSERT_EQUAL(*str_it, "first");
+    std::advance(str_it, 2);
+    ASSERT_EQUAL(*str_it, "third");
 #endif
     TEST_SUCCEED();
   }
 
+  bool test_extract_into() {
+    TEST_START();
+#if SIMDJSON_STATIC_REFLECTION
+    struct Car {
+      std::string make;
+      std::string model;
+      int year;
+      double price;
+      std::optional<std::string> color;
+    };
+
+    ondemand::parser parser;
+
+    // Test 1: Extract only specific fields
+    {
+      auto padded = R"({
+        "make": "Toyota",
+        "model": "Camry",
+        "year": 2024,
+        "price": 28999.99,
+        "color": "Blue",
+        "engine": "V6",
+        "transmission": "Automatic"
+      })"_padded;
+
+      Car car{};
+      ondemand::document doc;
+      ASSERT_SUCCESS( parser.iterate(padded).get(doc) );
+
+      ondemand::object obj;
+      ASSERT_SUCCESS(doc.get_object().get(obj));
+
+            // Extract only 'make' and 'model'
+      ASSERT_SUCCESS(obj.extract_into<"make","model">(car));
+
+      ASSERT_EQUAL(car.make, "Toyota");
+      ASSERT_EQUAL(car.model, "Camry");
+      ASSERT_EQUAL(car.year, 0);  // Not extracted
+      ASSERT_EQUAL(car.price, 0);  // Not extracted
+
+      ASSERT_SUCCESS(parser.iterate(padded).get(doc));
+
+      // Extract only 'make' and 'model'
+      ASSERT_SUCCESS(doc.extract_into<"make", "model">(car));
+
+      ASSERT_EQUAL(car.make, "Toyota");
+      ASSERT_EQUAL(car.model, "Camry");
+      ASSERT_EQUAL(car.year, 0);  // Not extracted
+      ASSERT_EQUAL(car.price, 0);  // Not extracted
+    }
+
+    // Test 2: Extract with optional field
+    {
+      auto padded = R"({
+        "make": "Honda",
+        "model": "Accord",
+        "year": 2023,
+        "price": 26999.99,
+        "color": "Red"
+      })"_padded;
+
+      Car car{};
+      ondemand::document doc;
+      ASSERT_SUCCESS(parser.iterate(padded).get(doc));
+
+      ondemand::object obj;
+      ASSERT_SUCCESS(doc.get_object().get(obj));
+
+      // Extract including optional 'color'
+      ASSERT_SUCCESS(obj.extract_into<"make", "model", "color">(car));
+
+      ASSERT_EQUAL(car.make, "Honda");
+      ASSERT_EQUAL(car.model, "Accord");
+      ASSERT_TRUE(car.color.has_value());
+      ASSERT_EQUAL(*car.color, "Red");
+    }
+
+    // Test 3: Extract with missing optional field
+    {
+      auto padded = R"({
+        "make": "Ford",
+        "model": "F-150",
+        "year": 2024,
+        "price": 35999.99
+      })"_padded;
+
+      Car car{};
+      ondemand::document doc;
+      ASSERT_SUCCESS(parser.iterate(padded).get(doc));
+
+      ondemand::object obj;
+      ASSERT_SUCCESS(doc.get_object().get(obj));
+
+      // Try to extract including optional 'color' which doesn't exist
+      ASSERT_SUCCESS(obj.extract_into<"make", "model", "color">(car));
+
+      ASSERT_EQUAL(car.make, "Ford");
+      ASSERT_EQUAL(car.model, "F-150");
+      ASSERT_FALSE(car.color.has_value());  // Should be empty
+    }
+
+    // Test 4: Extract with custom deserializable type using tag_invoke
+    {
+      // Test using the Price struct defined at namespace level
+
+      auto padded = R"({
+        "name": "Laptop",
+        "price": {
+          "amount": 1000,
+          "currency": "EUR"
+        },
+        "stock": 15,
+        "description": "High-end gaming laptop"
+      })"_padded;
+
+      Product product{};
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      ondemand::object obj;
+      auto obj_result = doc.get_object().get(obj);
+      ASSERT_SUCCESS(obj_result);
+
+      // Extract including price field with custom deserializer
+      ASSERT_SUCCESS(obj.extract_into<"name", "price">(product));
+
+      ASSERT_EQUAL(product.name, "Laptop");
+      // Verify custom deserializer was invoked: EUR should be converted to USD
+      ASSERT_EQUAL(product.price.currency, "USD");  // Should be converted from EUR
+      // Verify custom deserializer was invoked: amount should be 1100 (1000 * 1.1)
+      ASSERT_EQUAL(product.price.amount, 1100);  // Should be exactly 1100 after conversion
+      ASSERT_EQUAL(product.stock, 0);  // Not extracted
+    }
+
+    // Test 5: Extract with nested custom deserializable types
+    {
+      // Test using the Dimensions struct defined at namespace level
+
+      auto padded = R"({
+        "id": "PKG123",
+        "weight": {
+          "value": 10,
+          "unit": "pounds"
+        },
+        "length": {
+          "value": 12,
+          "unit": "inches"
+        },
+        "fragile": true
+      })"_padded;
+
+      Package pkg{};
+      ondemand::document doc;
+      ASSERT_SUCCESS(parser.iterate(padded).get(doc));
+
+      ondemand::object obj;
+      ASSERT_SUCCESS(doc.get_object().get(obj));
+
+      // Extract only length (with custom deserializer), skip weight
+      ASSERT_SUCCESS(obj.extract_into<"id", "length">(pkg));
+
+      ASSERT_EQUAL(pkg.id, "PKG123");
+      // Verify custom deserializer was invoked: inches should be converted to cm
+      ASSERT_EQUAL(pkg.length.unit, "cm");  // Should be converted from inches
+      // Verify exact conversion: 12 inches * 2.54 = 30.48 cm
+      ASSERT_EQUAL(pkg.length.value, 30.48);  // Should be exactly 30.48 after conversion
+      ASSERT_EQUAL(pkg.weight.unit, "");  // Weight not extracted
+      ASSERT_EQUAL(pkg.weight.value, 0);  // Weight value should remain at default
+    }
+#endif
+    TEST_SUCCEED();
+  }
+
+
+  bool test_extract_from() {
+    TEST_START();
+#if SIMDJSON_STATIC_REFLECTION
+    // Test 1: Extract specific fields from Car struct
+    {
+      struct Car {
+        std::string make;
+        std::string model;
+        int year;
+        double price;
+        bool electric;
+      };
+
+      Car car{"Tesla", "Model 3", 2023, 42000.0, true};
+
+      // Extract only make and model
+      std::string json;
+      ASSERT_SUCCESS((extract_from<"make", "model">(car).get(json)));
+
+      // Parse back to verify correctness
+      auto padded = pad(json);
+      ondemand::parser parser;
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      std::string_view make;
+      std::string_view model;
+      ASSERT_SUCCESS(doc["make"].get(make));
+      ASSERT_SUCCESS(doc["model"].get(model));
+      ASSERT_EQUAL(make, "Tesla");
+      ASSERT_EQUAL(model, "Model 3");
+
+      // Verify excluded fields are not present
+      auto year_result = doc["year"];
+      ASSERT_ERROR(year_result.error(), NO_SUCH_FIELD);
+      auto price_result = doc["price"];
+      ASSERT_ERROR(price_result.error(), NO_SUCH_FIELD);
+      auto electric_result = doc["electric"];
+      ASSERT_ERROR(electric_result.error(), NO_SUCH_FIELD);
+    }
+
+    // Test 2: Extract different field combination
+    {
+      struct Car {
+        std::string make;
+        std::string model;
+        int year;
+        double price;
+        bool electric;
+      };
+
+      Car car{"Ford", "F-150", 2024, 55000.0, false};
+
+      // Extract year and price
+      std::string json;
+      ASSERT_SUCCESS((extract_from<"year", "price">(car).get(json)));
+
+      auto padded = pad(json);
+      ondemand::parser parser;
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      int64_t year;
+      double price;
+      ASSERT_SUCCESS(doc["year"].get(year));
+      ASSERT_SUCCESS(doc["price"].get(price));
+      ASSERT_EQUAL(year, 2024);
+      ASSERT_EQUAL(price, 55000.0);
+
+      // Verify excluded fields
+      auto make_result = doc["make"];
+      ASSERT_ERROR(make_result.error(), NO_SUCH_FIELD);
+    }
+
+    // Test 3: Extract from struct with optional fields
+    {
+      struct Person {
+        std::string name;
+        int age;
+        std::optional<std::string> email;
+        std::optional<std::string> phone;
+      };
+
+      Person person{"John Doe", 30, "john@example.com", std::nullopt};
+
+      // Extract name and email
+      std::string json;
+      ASSERT_SUCCESS((extract_from<"name", "email">(person).get(json)));
+
+      auto padded = pad(json);
+      ondemand::parser parser;
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      std::string_view name;
+      std::string_view email;
+      ASSERT_SUCCESS(doc["name"].get(name));
+      ASSERT_SUCCESS(doc["email"].get(email));
+      ASSERT_EQUAL(name, "John Doe");
+      ASSERT_EQUAL(email, "john@example.com");
+    }
+
+    // Test 4: Extract with optional that has value
+    {
+      struct Person {
+        std::string name;
+        int age;
+        std::optional<std::string> email;
+        std::optional<std::string> phone;
+      };
+
+      Person person{"Jane Smith", 25, "jane@example.com", "555-1234"};
+
+      // Extract name, age, and phone
+      std::string json;
+      ASSERT_SUCCESS((extract_from<"name", "age", "phone">(person).get(json)));
+
+      auto padded = pad(json);
+      ondemand::parser parser;
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      std::string_view name;
+      int64_t age;
+      std::string_view phone;
+      ASSERT_SUCCESS(doc["name"].get(name));
+      ASSERT_SUCCESS(doc["age"].get(age));
+      ASSERT_SUCCESS(doc["phone"].get(phone));
+      ASSERT_EQUAL(name, "Jane Smith");
+      ASSERT_EQUAL(age, 25);
+      ASSERT_EQUAL(phone, "555-1234");
+
+      // Email should not be present
+      auto email_result = doc["email"];
+      ASSERT_ERROR(email_result.error(), NO_SUCH_FIELD);
+    }
+
+    // Test 5: Round-trip test - serialize with extract_from, deserialize with extract_into
+    {
+      struct Product {
+        std::string id;
+        std::string name;
+        double price;
+        int stock;
+      };
+
+      Product original{"P123", "Widget", 19.99, 100};
+
+      // Extract specific fields to JSON
+      std::string json;
+      ASSERT_SUCCESS((extract_from<"id", "name", "price">(original).get(json)));
+
+      // Parse and extract back
+      Product restored{"", "", 0.0, 0};
+      auto padded = pad(json);
+      ondemand::parser parser;
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      ondemand::object obj;
+      ASSERT_SUCCESS(doc.get_object().get(obj));
+      auto extract_result = obj.extract_into<"id", "name", "price">(restored);
+      ASSERT_SUCCESS(extract_result);
+
+      // Verify fields match
+      ASSERT_EQUAL(restored.id, original.id);
+      ASSERT_EQUAL(restored.name, original.name);
+      ASSERT_EQUAL(restored.price, original.price);
+      ASSERT_EQUAL(restored.stock, 0);  // Stock should remain at default
+    }
+
+    // Test 6: Extract from nested structs
+    {
+      struct Address {
+        std::string street;
+        std::string city;
+        std::string zip;
+      };
+
+      struct Company {
+        std::string name;
+        Address headquarters;
+        int employees;
+      };
+
+      Company company{"TechCorp", {"123 Main St", "San Francisco", "94105"}, 500};
+
+      // Extract name and employees only
+      std::string json;
+      ASSERT_SUCCESS((extract_from<"name", "employees">(company).get(json)));
+
+      auto padded = pad(json);
+      ondemand::parser parser;
+      auto doc = parser.iterate(padded);
+      ASSERT_SUCCESS(doc);
+
+      std::string_view name;
+      int64_t employees;
+      ASSERT_SUCCESS(doc["name"].get(name));
+      ASSERT_SUCCESS(doc["employees"].get(employees));
+      ASSERT_EQUAL(name, "TechCorp");
+      ASSERT_EQUAL(employees, 500);
+
+      // headquarters should not be present
+      auto hq_result = doc["headquarters"];
+      ASSERT_ERROR(hq_result.error(), NO_SUCH_FIELD);
+    }
+#endif
+    TEST_SUCCEED();
+  }
 
   bool run() {
     return test_primitive_types() &&
            test_string_types() &&
            test_optional_types() &&
            test_smart_pointer_types() &&
-           test_container_types();
+           test_container_types() &&
+           test_extract_into() &&
+           test_extract_from();
   }
 
 } // namespace builder_tests

tests/builder/static_reflection_custom_tests.cpp

@@ -0,0 +1,138 @@
+
+
+
+#include "simdjson.h"
+#include "test_builder.h"
+#include <charconv>
+#include <string>
+
+using namespace simdjson;
+
+// Suppose that we want to serialize/deserialize Car using
+// strings for the year
+struct Car {
+  std::string make;
+  std::string model;
+  int64_t year;
+  std::vector<float> tire_pressure;
+};
+
+
+
+namespace simdjson {
+// This tag_invoke MUST be inside simdjson namespace
+template <typename simdjson_value>
+auto tag_invoke(deserialize_tag, simdjson_value &val, Car& car) {
+  ondemand::object obj;
+  auto error = val.get_object().get(obj);
+  if (error) {
+    return error;
+  }
+  if ((error = obj["make"].get_string(car.make))) {
+    return error;
+  }
+  if ((error = obj["model"].get_string(car.model))) {
+    return error;
+  }
+  std::string_view year_str;
+  if ((error = obj["year"].get(year_str))) {
+    return error;
+  }
+  int64_t year_value;
+  auto [ptr, ec] = std::from_chars(year_str.data(), year_str.data() + year_str.size(), year_value);
+  if (ec != std::errc{}) {
+    return INCORRECT_TYPE;
+  }
+  car.year = year_value;
+  if ((error = obj["tire_pressure"].get<std::vector<float>>().get(
+           car.tire_pressure))) {
+    return error;
+  }
+  return simdjson::SUCCESS;
+}
+
+template <typename builder_type>
+void tag_invoke(serialize_tag, builder_type &builder, const Car& car) {
+  builder.start_object();
+  builder.append_key_value("make", car.make);
+  builder.append_comma();
+  builder.append_key_value("model", car.model);
+  builder.append_comma();
+  builder.append_key_value("year", std::to_string(car.year));
+  builder.append_comma();
+  builder.append_key_value("tire_pressure", car.tire_pressure);
+  builder.end_object();
+}
+
+} // namespace simdjson
+namespace custom_tests {
+
+  bool test_car_deserialization() {
+    TEST_START();
+    auto json = R"({"make":"Toyota","model":"Camry","year":"2018","tire_pressure":[30.5,30.6,30.7,30.8]})"_padded;
+    ondemand::parser parser;
+    auto doc_result = parser.iterate(json);
+    ASSERT_SUCCESS(doc_result);
+    Car car;
+    ASSERT_SUCCESS(doc_result.get(car));
+    if (car.make != "Toyota" || car.model != "Camry" || std::to_string(car.year) != "2018" || car.tire_pressure.size() != 4 || car.tire_pressure[0] != 30.5f) {
+      return false;
+    }
+    TEST_SUCCEED();
+  }
+  bool test_car_serialization() {
+    TEST_START();
+    Car car{"Toyota", "Camry", 2018, {30.5f,30.6f,30.7f,30.8f}};
+    simdjson::builder::string_builder builder;
+    builder.append(car);
+    std::string_view json;
+    ASSERT_SUCCESS(builder.view().get(json));
+    TEST_SUCCEED();
+  }
+  bool test_car_roundtrip() {
+    TEST_START();
+    Car car{"Toyota", "Camry", 2018, {30.5f,30.6f,30.7f,30.8f}};
+    simdjson::builder::string_builder builder;
+    builder.append(car);
+    std::string json;
+    ASSERT_SUCCESS(builder.view().get(json));
+    ondemand::parser parser;
+    auto doc_result = parser.iterate(json);
+    ASSERT_SUCCESS(doc_result);
+    Car carback;
+    ASSERT_SUCCESS(doc_result.get(carback));
+
+    if (carback.make != car.make || carback.model != car.model || carback.year != car.year || carback.tire_pressure != car.tire_pressure) {
+      return false;
+    }
+
+    TEST_SUCCEED();
+  }
+
+  bool test_car_roundtrip_to_json() {
+    TEST_START();
+    Car car{"Toyota", "Camry", 2018, {30.5f,30.6f,30.7f,30.8f}};
+    std::string json;
+    ASSERT_SUCCESS(simdjson::to_json(car).get(json));
+    simdjson::builder::string_builder builder;
+    ondemand::parser parser;
+    auto doc_result = parser.iterate(json);
+    ASSERT_SUCCESS(doc_result);
+    Car carback;
+    ASSERT_SUCCESS(doc_result.get(carback));
+
+    if (carback.make != car.make || carback.model != car.model || carback.year != car.year || carback.tire_pressure != car.tire_pressure) {
+      return false;
+    }
+
+    TEST_SUCCEED();
+  }
+  bool run() {
+    return test_car_deserialization() && test_car_serialization() && test_car_roundtrip() && test_car_roundtrip_to_json();
+  }
+
+} // namespace builder_tests
+
+int main(int argc, char *argv[]) {
+  return test_main(argc, argv, custom_tests::run);
+}

tests/builder/static_reflection_edge_cases_tests.cpp

@@ -28,10 +28,8 @@ namespace builder_tests {
     test.null_unique_ptr = nullptr;
     test.null_shared_ptr = nullptr;
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"empty_string\":\"\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"empty_vector\":[]") != std::string::npos);
     ASSERT_TRUE(json.find("\"null_optional\":null") != std::string::npos);
@@ -43,10 +41,8 @@ namespace builder_tests {
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
 
-    auto get_result = doc_result.value().get<EmptyValues>();
-    ASSERT_SUCCESS(get_result);
-
-    EmptyValues deserialized = std::move(get_result.value());
+    EmptyValues deserialized;
+    ASSERT_SUCCESS(doc_result.get<EmptyValues>().get(deserialized));
     ASSERT_EQUAL(deserialized.empty_string, "");
     ASSERT_EQUAL(deserialized.empty_vector.size(), 0);
     ASSERT_FALSE(deserialized.null_optional.has_value());
@@ -74,10 +70,8 @@ namespace builder_tests {
     test.unicode = "Café résumé";
     test.null_char = '\0';
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     // Test that quotes are properly escaped
     ASSERT_TRUE(json.find("\\\"Hello\\\"") != std::string::npos);
     // Test that backslashes are properly escaped
@@ -100,17 +94,17 @@ namespace builder_tests {
     test_no_null.newlines = test.newlines;
     test_no_null.unicode = test.unicode;
 
-    auto result_no_null = builder::to_json_string(test_no_null);
-    ASSERT_SUCCESS(result_no_null);
+    std::string result_no_null;
+    ASSERT_SUCCESS(builder::to_json_string(test_no_null).get(result_no_null));
 
     ondemand::parser parser;
-    auto doc_result = parser.iterate(pad(result_no_null.value()));
-    ASSERT_SUCCESS(doc_result);
+    ondemand::document doc_result;
 
-    auto get_result = doc_result.value().get<SpecialCharsNoNull>();
-    ASSERT_SUCCESS(get_result);
+    ASSERT_SUCCESS(parser.iterate(pad(result_no_null)).get(doc_result));
+
+    SpecialCharsNoNull deserialized;
+    ASSERT_SUCCESS(doc_result.get<SpecialCharsNoNull>().get(deserialized));
 
-    SpecialCharsNoNull deserialized = std::move(get_result.value());
     ASSERT_EQUAL(deserialized.quotes, test.quotes);
     ASSERT_EQUAL(deserialized.backslashes, test.backslashes);
     ASSERT_EQUAL(deserialized.newlines, test.newlines);
@@ -139,22 +133,18 @@ namespace builder_tests {
     test.true_val = true;
     test.false_val = false;
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"true_val\":true") != std::string::npos);
     ASSERT_TRUE(json.find("\"false_val\":false") != std::string::npos);
 
     // Test round-trip
     ondemand::parser parser;
-    auto doc_result = parser.iterate(pad(json));
-    ASSERT_SUCCESS(doc_result);
+    ondemand::document doc_result;
 
-    auto get_result = doc_result.value().get<NumericLimits>();
-    ASSERT_SUCCESS(get_result);
-
-    NumericLimits deserialized = std::move(get_result.value());
+    ASSERT_SUCCESS(parser.iterate(pad(json)).get(doc_result));
+    NumericLimits deserialized;
+    ASSERT_SUCCESS(doc_result.get<NumericLimits>().get(deserialized));
     ASSERT_EQUAL(deserialized.max_int, test.max_int);
     ASSERT_EQUAL(deserialized.min_int, test.min_int);
     ASSERT_EQUAL(deserialized.true_val, true);
@@ -184,10 +174,8 @@ namespace builder_tests {
     test.optional_inner = Inner{99, "optional"};
     test.unique_inner = std::make_unique<Inner>(Inner{123, "unique"});
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"inner_obj\":{") != std::string::npos);
     ASSERT_TRUE(json.find("\"inner_vector\":[") != std::string::npos);
     ASSERT_TRUE(json.find("\"optional_inner\":{") != std::string::npos);
@@ -198,10 +186,8 @@ namespace builder_tests {
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
 
-    auto get_result = doc_result.value().get<Outer>();
-    ASSERT_SUCCESS(get_result);
-
-    Outer deserialized = std::move(get_result.value());
+    Outer deserialized;
+    ASSERT_SUCCESS(doc_result.get<Outer>().get(deserialized));
     ASSERT_EQUAL(deserialized.inner_obj.value, 42);
     ASSERT_EQUAL(deserialized.inner_obj.name, "inner");
     ASSERT_EQUAL(deserialized.inner_vector.size(), 2);

tests/builder/static_reflection_enum_tests.cpp

@@ -21,26 +21,21 @@ namespace builder_tests {
     };
 
     EnumStruct test{Color::Red, 42};
-
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     // Enum should be serialized as string (Red)
     ASSERT_TRUE(json.find("\"color\":\"Red\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"value\":42") != std::string::npos);
 
     // Test different enum values
     test.color = Color::Green;
-    auto result2 = builder::to_json_string(test);
-    ASSERT_SUCCESS(result2);
-    std::string json2 = result2.value();
+    std::string json2;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json2));
     ASSERT_TRUE(json2.find("\"color\":\"Green\"") != std::string::npos);
 
     test.color = Color::Blue;
-    auto result3 = builder::to_json_string(test);
-    ASSERT_SUCCESS(result3);
-    std::string json3 = result3.value();
+    std::string json3;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json3));
     ASSERT_TRUE(json3.find("\"color\":\"Blue\"") != std::string::npos);
 #endif
     TEST_SUCCEED();
@@ -61,41 +56,37 @@ namespace builder_tests {
     };
 
     // Test deserialization of different enum values with string representation
-    std::string json1 = "{\"status\":\"Active\",\"name\":\"test1\"}";
+    auto json1 = R"({"status":"Active","name":"test1"})"_padded;
     ondemand::parser parser1;
-    auto doc_result1 = parser1.iterate(pad(json1));
-    ASSERT_SUCCESS(doc_result1);
+    ondemand::document doc_result1;
+    ASSERT_SUCCESS(parser1.iterate(json1).get(doc_result1));
+    StatusStruct deserialized1;
+    ASSERT_SUCCESS(doc_result1.get<StatusStruct>().get(deserialized1));
 
-    auto get_result1 = doc_result1.value().get<StatusStruct>();
-    ASSERT_SUCCESS(get_result1);
-
-    StatusStruct deserialized1 = std::move(get_result1.value());
     ASSERT_TRUE(deserialized1.status == Status::Active);
     ASSERT_EQUAL(deserialized1.name, "test1");
 
     // Test Status::Inactive
-    std::string json2 = "{\"status\":\"Inactive\",\"name\":\"test2\"}";
+    auto json2 = R"({"status":"Inactive","name":"test2"})"_padded;
     ondemand::parser parser2;
-    auto doc_result2 = parser2.iterate(pad(json2));
-    ASSERT_SUCCESS(doc_result2);
+    ondemand::document doc_result2;
+    ASSERT_SUCCESS(parser2.iterate(json2).get(doc_result2));
 
-    auto get_result2 = doc_result2.value().get<StatusStruct>();
-    ASSERT_SUCCESS(get_result2);
+    StatusStruct deserialized2;
+    ASSERT_SUCCESS(doc_result2.get<StatusStruct>().get(deserialized2));
 
-    StatusStruct deserialized2 = std::move(get_result2.value());
     ASSERT_TRUE(deserialized2.status == Status::Inactive);
     ASSERT_EQUAL(deserialized2.name, "test2");
 
     // Test Status::Pending
     std::string json3 = "{\"status\":\"Pending\",\"name\":\"test3\"}";
     ondemand::parser parser3;
-    auto doc_result3 = parser3.iterate(pad(json3));
-    ASSERT_SUCCESS(doc_result3);
+    ondemand::document doc_result3;
+    ASSERT_SUCCESS(parser3.iterate(pad(json3)).get(doc_result3));
 
-    auto get_result3 = doc_result3.value().get<StatusStruct>();
-    ASSERT_SUCCESS(get_result3);
+    StatusStruct deserialized3;
+    ASSERT_SUCCESS(doc_result3.get<StatusStruct>().get(deserialized3));
 
-    StatusStruct deserialized3 = std::move(get_result3.value());
     ASSERT_TRUE(deserialized3.status == Status::Pending);
     ASSERT_EQUAL(deserialized3.name, "test3");
 #endif
@@ -121,10 +112,8 @@ namespace builder_tests {
     Task original{Priority::High, "Important task", 123};
 
     // Serialize
-    auto serialize_result = builder::to_json_string(original);
-    ASSERT_SUCCESS(serialize_result);
-
-    std::string json = serialize_result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(original).get(json));
     ASSERT_TRUE(json.find("\"priority\":\"High\"") != std::string::npos); // High as string
     ASSERT_TRUE(json.find("\"description\":\"Important task\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"id\":123") != std::string::npos);
@@ -132,13 +121,12 @@ namespace builder_tests {
     // Deserialize
     ondemand::parser parser;
     std::cout << json << std::endl;
-    auto doc_result = parser.iterate(pad(json));
-    ASSERT_SUCCESS(doc_result);
+    ondemand::document doc_result;
+    ASSERT_SUCCESS(parser.iterate(pad(json)).get(doc_result));
 
-    auto get_result = doc_result.value().get<Task>();
-    ASSERT_SUCCESS(get_result);
+    Task deserialized;
+    ASSERT_SUCCESS(doc_result.get<Task>().get(deserialized));
 
-    Task deserialized = std::move(get_result.value());
     ASSERT_TRUE(deserialized.priority == Priority::High);
     ASSERT_EQUAL(deserialized.description, "Important task");
     ASSERT_EQUAL(deserialized.id, 123);
@@ -162,22 +150,18 @@ namespace builder_tests {
 
     Response test{ErrorCode::NotFound, "Resource not found"};
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"error\":\"NotFound\"") != std::string::npos);
     ASSERT_TRUE(json.find("\"message\":\"Resource not found\"") != std::string::npos);
 
     // Test round-trip
     ondemand::parser parser;
-    auto doc_result = parser.iterate(pad(json));
-    ASSERT_SUCCESS(doc_result);
+    ondemand::document doc_result;
+    ASSERT_SUCCESS(parser.iterate(pad(json)).get(doc_result));
+    Response deserialized;
+    ASSERT_SUCCESS(doc_result.get<Response>().get(deserialized));
 
-    auto get_result = doc_result.value().get<Response>();
-    ASSERT_SUCCESS(get_result);
-
-    Response deserialized = std::move(get_result.value());
     ASSERT_TRUE(deserialized.error == ErrorCode::NotFound);
     ASSERT_EQUAL(deserialized.message, "Resource not found");
 #endif
@@ -220,10 +204,8 @@ namespace builder_tests {
 
     Date test{Day::Friday, Month::July, 2024};
 
-    auto result = builder::to_json_string(test);
-    ASSERT_SUCCESS(result);
-
-    std::string json = result.value();
+    std::string json;
+    ASSERT_SUCCESS(builder::to_json_string(test).get(json));
     ASSERT_TRUE(json.find("\"day\":\"Friday\"") != std::string::npos);      // Friday as string
     ASSERT_TRUE(json.find("\"month\":\"July\"") != std::string::npos);    // July as string
     ASSERT_TRUE(json.find("\"year\":2024") != std::string::npos);
@@ -232,11 +214,8 @@ namespace builder_tests {
     ondemand::parser parser;
     auto doc_result = parser.iterate(pad(json));
     ASSERT_SUCCESS(doc_result);
-
-    auto get_result = doc_result.value().get<Date>();
-    ASSERT_SUCCESS(get_result);
-
-    Date deserialized = std::move(get_result.value());
+    Date deserialized;
+    ASSERT_SUCCESS(doc_result.get<Date>().get(deserialized));
     ASSERT_TRUE(deserialized.day == Day::Friday);
     ASSERT_TRUE(deserialized.month == Month::July);
     ASSERT_EQUAL(deserialized.year, 2024);

tests/dom/CMakeLists.txt

@@ -123,7 +123,7 @@ endif()
 
 # Add the tests if we're on:
 #   1. Visual Studio 2022 v17.6 or later
-#   2. GCC v14.0.0 or later (GCC v13.0.0 cannot handle pipe oprator of lambda)
+#   2. GCC v14.0.0 or later (GCC v13.0.0 cannot handle pipe operator of lambda)
 #   3. Clang v15.0.0 or later (certain version C++ headers occur error when compiling)
 if(
   (MSVC AND MSVC_VERSION LESS 1930) OR

tests/dom/ranges_test.cpp

@@ -8,7 +8,7 @@
 
 using namespace simdjson;
 namespace ranges_test {
-
+#if SIMDJSON_EXCEPTIONS
   bool printout() {
     TEST_START();
     auto cars_json = R"( [
@@ -43,6 +43,7 @@ namespace ranges_test {
     ASSERT_TRUE(std::ranges::equal(cars, expected));
     TEST_SUCCEED();
   }
+  #endif // SIMDJSON_EXCEPTIONS
 
   bool run() {
     return

tests/ondemand/compile_time_json_tests.cpp

@@ -0,0 +1,418 @@
+/**
+ * @file compile_time_json_tests.cpp
+ * @brief Comprehensive tests for compile-time JSON parsing using C++26 P2996 reflection
+ */
+
+#include "simdjson.h"
+#include "test_ondemand.h"
+
+using namespace simdjson;
+using namespace std::string_view_literals;
+
+namespace compile_time_json_tests {
+
+#if SIMDJSON_STATIC_REFLECTION
+using namespace arm64::compile_time;
+#endif
+
+/**
+ * Test 1: Basic object with primitives
+ */
+bool test_basic_object() {
+    TEST_START();
+
+    constexpr auto config = parse_json<R"({
+        "port": 8080,
+        "host": "localhost",
+        "debug": true,
+        "timeout": 30.5
+    })">();
+
+    static_assert(config.port == 8080);
+    static_assert(std::string_view(config.host) == "localhost");
+    static_assert(config.debug == true);
+    static_assert(config.timeout == 30.5);
+
+    ASSERT_EQUAL(config.port, 8080);
+    ASSERT_EQUAL(std::string_view(config.host), "localhost"sv);
+    ASSERT_TRUE(config.debug);
+    ASSERT_EQUAL(config.timeout, 30.5);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 2: Nested objects
+ */
+bool test_nested_objects() {
+    TEST_START();
+
+    constexpr auto config = parse_json<R"({
+        "server_port": 3000,
+        "enable_ssl": true,
+        "database": {
+            "host": "db.example.com",
+            "port": 5432,
+            "timeout_sec": 30.0
+        }
+    })">();
+
+    static_assert(config.server_port == 3000);
+    static_assert(config.enable_ssl == true);
+    static_assert(std::string_view(config.database.host) == "db.example.com");
+    static_assert(config.database.port == 5432);
+    static_assert(config.database.timeout_sec == 30.0);
+
+    ASSERT_EQUAL(config.server_port, 3000);
+    ASSERT_TRUE(config.enable_ssl);
+    ASSERT_EQUAL(std::string_view(config.database.host), "db.example.com"sv);
+    ASSERT_EQUAL(config.database.port, 5432);
+    ASSERT_EQUAL(config.database.timeout_sec, 30.0);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 3: Deeply nested objects (3+ levels)
+ */
+bool test_deeply_nested_objects() {
+    TEST_START();
+
+    constexpr auto config = parse_json<R"({
+        "app_name": "MyApp",
+        "version": 1.5,
+        "server": {
+            "host": "api.example.com",
+            "port": 443,
+            "tls": {
+                "enabled": true,
+                "cert_path": "/etc/ssl/cert.pem",
+                "min_version": 1.3
+            }
+        }
+    })">();
+
+    static_assert(std::string_view(config.app_name) == "MyApp");
+    static_assert(config.version == 1.5);
+    static_assert(std::string_view(config.server.host) == "api.example.com");
+    static_assert(config.server.port == 443);
+    static_assert(config.server.tls.enabled == true);
+    static_assert(std::string_view(config.server.tls.cert_path) == "/etc/ssl/cert.pem");
+    static_assert(config.server.tls.min_version == 1.3);
+
+    ASSERT_EQUAL(std::string_view(config.app_name), "MyApp"sv);
+    ASSERT_EQUAL(config.server.tls.enabled, true);
+    ASSERT_EQUAL(config.server.tls.min_version, 1.3);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 4: Empty object
+ */
+bool test_empty_object() {
+    TEST_START();
+
+    constexpr auto config = parse_json<"{}">();
+    (void)config;  // Suppress unused warning
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 5: Negative numbers
+ */
+bool test_negative_numbers() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"({
+        "temperature": -273.15,
+        "count": -42
+    })">();
+
+    static_assert(data.temperature == -273.15);
+    static_assert(data.count == -42);
+
+    ASSERT_EQUAL(data.temperature, -273.15);
+    ASSERT_EQUAL(data.count, -42);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 6: Whitespace handling
+ */
+bool test_whitespace() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"(
+        {
+            "key1"  :  "value1"  ,
+            "key2"  :  42
+        }
+    )">();
+
+    static_assert(std::string_view(data.key1) == "value1");
+    static_assert(data.key2 == 42);
+
+    ASSERT_EQUAL(std::string_view(data.key1), "value1"sv);
+    ASSERT_EQUAL(data.key2, 42);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 7: Real-time system configuration
+ */
+bool test_realtime_config() {
+    TEST_START();
+
+    constexpr auto config = parse_json<R"({
+        "control_loop_hz": 1000,
+        "max_acceleration": 9.8,
+        "min_velocity": -50.0,
+        "max_velocity": 50.0,
+        "enable_safety_checks": true,
+        "log_level": "INFO"
+    })">();
+
+    static_assert(config.control_loop_hz == 1000);
+    static_assert(config.max_acceleration == 9.8);
+    static_assert(config.enable_safety_checks == true);
+
+    ASSERT_EQUAL(config.control_loop_hz, 1000);
+    ASSERT_EQUAL(config.max_acceleration, 9.8);
+    ASSERT_EQUAL(config.min_velocity, -50.0);
+    ASSERT_EQUAL(config.max_velocity, 50.0);
+    ASSERT_TRUE(config.enable_safety_checks);
+    ASSERT_EQUAL(std::string_view(config.log_level), "INFO"sv);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 8: External JSON file (future #embed support)
+ */
+bool test_external_json_embed() {
+    TEST_START();
+
+    // Future C++26 with #embed:
+    // constexpr auto config = parse_json<#embed "test_config.json">();
+
+    // Current workaround - inline the JSON from test_config.json
+    constexpr auto config = parse_json<R"({
+  "system_name": "RealTimeController",
+  "version": "2.1.0",
+  "control_loop_hz": 1000,
+  "max_latency_us": 500,
+  "enable_diagnostics": true,
+  "log_level": "INFO"
+})">();
+
+    static_assert(std::string_view(config.system_name) == "RealTimeController");
+    static_assert(std::string_view(config.version) == "2.1.0");
+    static_assert(config.control_loop_hz == 1000);
+    static_assert(config.max_latency_us == 500);
+    static_assert(config.enable_diagnostics == true);
+    static_assert(std::string_view(config.log_level) == "INFO");
+
+    ASSERT_EQUAL(std::string_view(config.system_name), "RealTimeController"sv);
+    ASSERT_EQUAL(std::string_view(config.version), "2.1.0"sv);
+    ASSERT_EQUAL(config.control_loop_hz, 1000);
+    ASSERT_EQUAL(config.max_latency_us, 500);
+    ASSERT_TRUE(config.enable_diagnostics);
+    ASSERT_EQUAL(std::string_view(config.log_level), "INFO"sv);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 9: JSON validation
+ */
+bool test_json_validation() {
+    TEST_START();
+
+    static_assert(validate_json<R"({"valid": true})">());
+    static_assert(validate_json<R"({"nested": {"deep": 42}})">());
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 10: Null values
+ */
+bool test_null_values() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"({
+        "nullable_field": null,
+        "number": 42
+    })">();
+
+    static_assert(data.nullable_field == nullptr);
+    static_assert(data.number == 42);
+
+    ASSERT_EQUAL(data.nullable_field, nullptr);
+    ASSERT_EQUAL(data.number, 42);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 11: Arrays of primitives
+ */
+bool test_arrays_primitives() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"({
+        "values": [1, 2, 3, 4, 5],
+        "flags": [true, false, true]
+    })">();
+
+    static_assert(data.values.size() == 5);
+    static_assert(data.values[0] == 1);
+    static_assert(data.values[4] == 5);
+    static_assert(data.flags.size() == 3);
+    static_assert(data.flags[0] == true);
+    static_assert(data.flags[1] == false);
+
+    ASSERT_EQUAL(data.values.size(), 5);
+    ASSERT_EQUAL(data.values[0], 1);
+    ASSERT_EQUAL(data.values[4], 5);
+    ASSERT_EQUAL(data.flags.size(), 3);
+    ASSERT_TRUE(data.flags[0]);
+    ASSERT_FALSE(data.flags[1]);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 12: Arrays of objects
+ */
+bool test_arrays_of_objects() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"({
+        "users": [
+            {"name": "Alice", "age": 30},
+            {"name": "Bob", "age": 25}
+        ]
+    })">();
+
+    static_assert(data.users.size() == 2);
+    static_assert(std::string_view(data.users[0].name) == "Alice");
+    static_assert(data.users[0].age == 30);
+    static_assert(std::string_view(data.users[1].name) == "Bob");
+    static_assert(data.users[1].age == 25);
+
+    ASSERT_EQUAL(data.users.size(), 2);
+    ASSERT_EQUAL(std::string_view(data.users[0].name), "Alice"sv);
+    ASSERT_EQUAL(data.users[0].age, 30);
+    ASSERT_EQUAL(std::string_view(data.users[1].name), "Bob"sv);
+    ASSERT_EQUAL(data.users[1].age, 25);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 13: Nested arrays in objects
+ */
+bool test_nested_arrays() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"({
+        "config": {
+            "ports": [8080, 8081, 8082]
+        }
+    })">();
+
+    static_assert(data.config.ports.size() == 3);
+    static_assert(data.config.ports[0] == 8080);
+    static_assert(data.config.ports[2] == 8082);
+
+    ASSERT_EQUAL(data.config.ports.size(), 3);
+    ASSERT_EQUAL(data.config.ports[0], 8080);
+    ASSERT_EQUAL(data.config.ports[2], 8082);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 14: Complex mixed structure with arrays and nested objects
+ */
+bool test_complex_mixed() {
+    TEST_START();
+
+    constexpr auto config = parse_json<R"({
+        "app": "myapp",
+        "version": 1.0,
+        "config": {
+            "ports": [8080, 8081, 8082],
+            "enabled": true
+        },
+        "servers": [
+            {"host": "server1", "port": 3000},
+            {"host": "server2", "port": 3001}
+        ]
+    })">();
+
+    static_assert(std::string_view(config.app) == "myapp");
+    static_assert(config.version == 1.0);
+    static_assert(config.config.ports[0] == 8080);
+    static_assert(config.config.enabled == true);
+    static_assert(std::string_view(config.servers[0].host) == "server1");
+    static_assert(config.servers[1].port == 3001);
+
+    ASSERT_EQUAL(std::string_view(config.app), "myapp"sv);
+    ASSERT_EQUAL(config.config.ports[0], 8080);
+    ASSERT_EQUAL(std::string_view(config.servers[0].host), "server1"sv);
+    ASSERT_EQUAL(config.servers[1].port, 3001);
+
+    TEST_SUCCEED();
+}
+
+/**
+ * Test 15: Empty arrays
+ */
+bool test_empty_arrays() {
+    TEST_START();
+
+    constexpr auto data = parse_json<R"({
+        "empty": []
+    })">();
+
+    static_assert(data.empty.size() == 0);
+
+    ASSERT_EQUAL(data.empty.size(), 0);
+
+    TEST_SUCCEED();
+}
+
+bool run() {
+    return test_basic_object() &&
+           test_nested_objects() &&
+           test_deeply_nested_objects() &&
+           test_empty_object() &&
+           test_negative_numbers() &&
+           test_whitespace() &&
+           test_realtime_config() &&
+           test_external_json_embed() &&
+           test_json_validation() &&
+           test_null_values() &&
+           test_arrays_primitives() &&
+           test_arrays_of_objects() &&
+           test_nested_arrays() &&
+           test_complex_mixed() &&
+           test_empty_arrays();
+}
+
+} // namespace compile_time_json_tests
+
+int main(int argc, char *argv[]) {
+#if SIMDJSON_STATIC_REFLECTION
+    return test_main(argc, argv, compile_time_json_tests::run);
+#else
+    std::cout << "Compile-time JSON tests require SIMDJSON_STATIC_REFLECTION=ON" << std::endl;
+    return EXIT_SUCCESS;
+#endif
+}

tests/ondemand/ondemand_array_tests.cpp

@@ -375,7 +375,7 @@ namespace array_tests {
       ASSERT_EQUAL(i*sizeof(uint64_t), sizeof(expected_value));
       std::vector<int64_t> container(i); // container of size 'i'.
 
-      doc_result.rewind();
+      ASSERT_SUCCESS( doc_result.rewind() );
       ASSERT_RESULT( doc_result.type(), json_type::array );
       ASSERT_SUCCESS( doc_result.get(array) );
       i = 0;
@@ -783,7 +783,7 @@ namespace array_tests {
       for (auto value : array) { (void) value; i++; }
       ASSERT_EQUAL(i, 0);
 
-      doc_result.rewind();
+      ASSERT_SUCCESS( doc_result.rewind() );
       ASSERT_RESULT( doc_result.type(), json_type::array );
       ASSERT_SUCCESS( doc_result.get(array) );
       i = 0;

tests/ondemand/ondemand_cacheline.cpp

@@ -23,7 +23,7 @@ long page_size() {
 // page boundary.
 bool need_allocation(const char *buf, size_t len) {
   return ((reinterpret_cast<uintptr_t>(buf + len - 1) % page_size())
-    + simdjson::SIMDJSON_PADDING > static_cast<uintptr_t>(page_size()));
+    + simdjson::SIMDJSON_PADDING >= static_cast<uintptr_t>(page_size()));
 }
 
 bool check_need_allocation() {

tests/ondemand/ondemand_convert_tests.cpp

@@ -2,6 +2,7 @@
 #include "simdjson/convert.h"
 #include "test_ondemand.h"
 
+#include <chrono>
 #include <map>
 #include <ranges>
 #include <string>
@@ -21,6 +22,24 @@ private:
     std::string date_str;
 };
 
+
+struct Meeting {
+    std::string title;
+    std::vector<std::string> attendees;
+    std::optional<std::string> location;
+    bool is_recurring;
+};
+
+
+struct MeetingTime {
+    std::string title;
+    std::chrono::system_clock::time_point start_time;
+    std::vector<std::string> attendees;
+    std::optional<std::string> location;
+    bool is_recurring;
+};
+
+
 namespace simdjson {
 template <typename simdjson_value>
 auto tag_invoke(deserialize_tag, simdjson_value &val, MyDate& date) {
@@ -43,57 +62,6 @@ struct complicated_weather_data {
 #ifdef __cpp_lib_ranges
 
 namespace convert_tests {
-#if SIMDJSON_EXCEPTIONS && SIMDJSON_SUPPORTS_CONCEPTS
-struct Car {
-  std::string make{};
-  std::string model{};
-  int year{};
-  std::vector<double> tire_pressure{};
-
-  friend simdjson::error_code tag_invoke(simdjson::deserialize_tag, auto &val,
-                                         Car &car) {
-    simdjson::ondemand::object obj;
-    auto error = val.get_object().get(obj);
-    if (error) {
-      return error;
-    }
-    // Instead of repeatedly obj["something"], we iterate through the object
-    // which we expect to be faster.
-    for (auto field : obj) {
-      simdjson::ondemand::raw_json_string key;
-      error = field.key().get(key);
-      if (error) {
-        return error;
-      }
-      if (key == "make") {
-        error = field.value().get_string(car.make);
-        if (error) {
-          return error;
-        }
-      } else if (key == "model") {
-        error = field.value().get_string(car.model);
-        if (error) {
-          return error;
-        }
-      } else if (key == "year") {
-        error = field.value().get(car.year);
-        if (error) {
-          return error;
-        }
-      } else if (key == "tire_pressure") {
-        error = field.value().get(car.tire_pressure);
-        if (error) {
-          return error;
-        }
-      }
-    }
-    return simdjson::SUCCESS;
-  }
-};
-
-static_assert(simdjson::custom_deserializable<std::unique_ptr<Car>>,
-              "It should be deserializable");
-
 
 simdjson::padded_string json_car =
     R"( {
@@ -111,22 +79,114 @@ simdjson::padded_string json_cars =
        "tire_pressure": [ 29.8, 30.0 ] }
 ])"_padded;
 
-bool simple() {
-  TEST_START();
-  Car car = simdjson::from(json_car);
-  if (car.make != "Toyota" || car.model != "Camry" || car.year != 2018) {
-    return false;
+#if SIMDJSON_SUPPORTS_CONCEPTS
+  struct Car {
+    std::string make{};
+    std::string model{};
+    int year{};
+    std::vector<double> tire_pressure{};
+
+    friend simdjson::error_code tag_invoke(simdjson::deserialize_tag, auto &val,
+                                          Car &car) {
+      simdjson::ondemand::object obj;
+      auto error = val.get_object().get(obj);
+      if (error) {
+        return error;
+      }
+      // Instead of repeatedly obj["something"], we iterate through the object
+      // which we expect to be faster.
+      for (auto field : obj) {
+        simdjson::ondemand::raw_json_string key;
+        error = field.key().get(key);
+        if (error) {
+          return error;
+        }
+        if (key == "make") {
+          error = field.value().get_string(car.make);
+          if (error) {
+            return error;
+          }
+        } else if (key == "model") {
+          error = field.value().get_string(car.model);
+          if (error) {
+            return error;
+          }
+        } else if (key == "year") {
+          error = field.value().get(car.year);
+          if (error) {
+            return error;
+          }
+        } else if (key == "tire_pressure") {
+          error = field.value().get(car.tire_pressure);
+          if (error) {
+            return error;
+          }
+        }
+      }
+      return simdjson::SUCCESS;
+    }
+  };
+
+  static_assert(simdjson::custom_deserializable<std::unique_ptr<Car>>,
+                "It should be deserializable");
+
+
+  bool simple_no_except() {
+    TEST_START();
+    Car car;
+    ASSERT_SUCCESS(simdjson::from(json_car).get(car));
+    if (car.make != "Toyota" || car.model != "Camry" || car.year != 2018) {
+      return false;
+    }
+    TEST_SUCCEED();
   }
-  TEST_SUCCEED();
-}
-
+#endif // SIMDJSON_SUPPORTS_CONCEPTS
+#if SIMDJSON_EXCEPTIONS && SIMDJSON_SUPPORTS_CONCEPTS
 
+  bool simple() {
+    TEST_START();
+    Car car = simdjson::from(json_car);
+    if (car.make != "Toyota" || car.model != "Camry" || car.year != 2018) {
+      return false;
+    }
+    TEST_SUCCEED();
+  }
+  struct Player {
+      std::string username;
+      int level;
+      double health;
+  };
   struct BadPlayer {
       int username;  // Oops, should be string!
       int level;
       double health;
   };
+  struct OptionalPlayer {
+      std::string username;
+      std::optional<int> level;
+      double health;
+  };
 #if SIMDJSON_STATIC_REFLECTION
+  bool missing_key_player() {
+    TEST_START();
+    std::string json = R"({"username":"Alice","health":100.0})";
+    simdjson::padded_string padded(json);
+    Player p;
+    simdjson::ondemand::parser parser;
+    auto doc = parser.iterate(padded);
+    ASSERT_ERROR(doc.get(p), simdjson::NO_SUCH_FIELD);
+    TEST_SUCCEED();
+  }
+  bool missing_key_optional_player() {
+    TEST_START();
+    std::string json = R"({"username":"Alice","health":100.0})";
+    simdjson::padded_string padded(json);
+    OptionalPlayer p;
+    simdjson::ondemand::parser parser;
+    auto doc = parser.iterate(padded);
+    ASSERT_SUCCESS(doc.get(p));
+    TEST_SUCCEED();
+  }
   bool bad_player() {
     TEST_START();
     // username is a string but we declared it as an int
@@ -160,7 +220,39 @@ bool simple() {
     ASSERT_SUCCESS(doc.get(p));
     TEST_SUCCEED();
   }
-#endif
+
+
+  bool meeting_test() {
+    TEST_START();
+    std::string json = simdjson::to_json(Meeting{
+        .title = "CppCon Planning",
+        .attendees = {"Alice", "Bob", "Charlie"},
+        .location = "Denver",
+        .is_recurring = true
+    });
+    Meeting m2 = simdjson::from(json);
+    std::cout << m2.title << std::endl;
+    TEST_SUCCEED();
+  }
+  bool meeting_time_test() {
+    TEST_START();
+    auto start_time = std::chrono::system_clock::now();
+    std::string json = simdjson::to_json(MeetingTime{
+        .title = "CppCon Planning",
+        .start_time = start_time,
+        .attendees = {"Alice", "Bob", "Charlie"},
+        .location = "Denver",
+        .is_recurring = true
+    });
+    std::cout << json << std::endl;
+    MeetingTime m2 = simdjson::from(json);
+    //ASSERT_EQUAL(m2.start_time, start_time);
+    std::cout << m2.title << std::endl;
+    TEST_SUCCEED();
+  }
+
+
+#endif // SIMDJSON_STATIC_REFLECTION
 bool broken() {
   TEST_START();
   simdjson::padded_string short_json_cars = R"( { "make )"_padded;
@@ -377,15 +469,6 @@ bool test_to_adaptor_with_single_value() {
   if (obj_result.error()) {
     return false;
   }
-/*  simdjson::ondemand::object obj = std::move(obj_result.value());
-
-  // We deliberately omit this part because simdjson::to has been removed.
-  auto year_val = obj["year"];
-  int64_t year = simdjson::to<int64_t>(year_val);
-  if (year != 2018) {
-    return false;
-  }
-*/
 
   TEST_SUCCEED();
 }
@@ -414,8 +497,11 @@ bool test_to_vs_from_equivalence() {
 #endif // SIMDJSON_EXCEPTIONS
 bool run() {
   return
-#if SIMDJSON_STATIC_REFLECTION
-      bad_player() && good_player() && complicated_weather_test() &&
+#if SIMDJSON_STATIC_REFLECTION && SIMDJSON_EXCEPTIONS && SIMDJSON_SUPPORTS_CONCEPTS
+      missing_key_optional_player() && missing_key_player() && meeting_time_test() && meeting_test() && bad_player() && good_player() && complicated_weather_test() &&
+#endif
+#if SIMDJSON_SUPPORTS_CONCEPTS
+      simple_no_except() &&
 #endif
 #if SIMDJSON_EXCEPTIONS && SIMDJSON_SUPPORTS_CONCEPTS
       broken() && simple() && simple_optional() && with_parser() && to_array() &&

tests/ondemand/ondemand_object_tests.cpp

@@ -485,7 +485,7 @@ namespace object_tests {
         i++;
       }
       ASSERT_EQUAL( i*sizeof(uint64_t), sizeof(expected_value) );
-      doc_result.rewind();
+      ASSERT_SUCCESS( doc_result.rewind() );
       ASSERT_RESULT( doc_result.type(), json_type::object );
       ASSERT_SUCCESS( doc_result.get(object) );
       i = 0;

tests/ondemand/ondemand_readme_examples.cpp

@@ -233,10 +233,47 @@ bool to_string_example() {
   ondemand::parser parser;
   ondemand::document doc = parser.iterate(json);
   std::string name;
-  doc["name"].get_string(name);
+  ASSERT_SUCCESS(doc["name"].get_string(name));
   ASSERT_EQUAL(name, "Daniel");
   TEST_SUCCEED();
 }
+#if SIMDJSON_STATIC_REFLECTION
+bool partial_car_extract() {
+  TEST_START();
+  auto json = R"( {
+         "make": "Toyota",
+         "model": "Camry",
+         "year": 2024,
+         "tire_pressure": [ 40.1, 39.9 ]
+       } )"_padded;
+  ondemand::parser parser;
+  ondemand::document doc = parser.iterate(json);
+  Car car{};
+  ASSERT_SUCCESS( (doc.extract_into<"make","model">(car)) );
+  ASSERT_EQUAL(car.make, "Toyota");
+  ASSERT_EQUAL(car.model, "Camry");
+  ASSERT_EQUAL(car.year, 0);  // Not extracted
+  ASSERT_EQUAL(car.tire_pressure.size(), 0); // Not extracted
+  TEST_SUCCEED();
+}
+
+bool temperature_example() {
+  TEST_START();
+  struct complicated_weather_data {
+    std::vector<std::string> time;
+    std::vector<float> temperature;
+  };
+  auto padded = R"({"time":["2023-03-15T12:00:00Z"],"temperature":[42]})"_padded;
+  simdjson::ondemand::parser parser;
+  simdjson::ondemand::document doc = parser.iterate(padded);
+  complicated_weather_data p = doc.get<complicated_weather_data>();
+  ASSERT_EQUAL(p.time.size(), 1);
+  ASSERT_EQUAL(p.time[0], "2023-03-15T12:00:00Z");
+  ASSERT_EQUAL(p.temperature.size(), 1);
+  ASSERT_EQUAL(p.temperature[0], 42);
+  TEST_SUCCEED();
+}
+#endif // SIMDJSON_STATIC_REFLECTION
 
 bool gen_raw1() {
   TEST_START();

tests/ondemand/test_config.json

@@ -0,0 +1,8 @@
+{
+  "system_name": "RealTimeController",
+  "version": "2.1.0",
+  "control_loop_hz": 1000,
+  "max_latency_us": 500,
+  "enable_diagnostics": true,
+  "log_level": "INFO"
+}

tests/test_macros.h

@@ -130,7 +130,7 @@ simdjson_inline bool assert_iterate_error(T &arr, simdjson::error_code expected,
 #define SUBTEST(NAME, TEST)             do { std::cout << " - Subtest " << (NAME) << " ..." << std::endl; if (!(TEST)) { return false; } } while (0);
 #define ASSERT_EQUAL(ACTUAL, EXPECTED)  do { if (!::assert_equal  ((ACTUAL), (EXPECTED), #ACTUAL)) { return false; } } while (0);
 #define ASSERT_RESULT(ACTUAL, EXPECTED) do { if (!::assert_result ((ACTUAL), (EXPECTED), #ACTUAL)) { return false; } } while (0);
-#define ASSERT_SUCCESS(ACTUAL)          do { if (!::assert_success((ACTUAL),             #ACTUAL)) { return false; } } while (0);
+#define ASSERT_SUCCESS(...)          do { if (!::assert_success((__VA_ARGS__),             #__VA_ARGS__)) { return false; } } while (0);
 #define ASSERT_FAILURE(ACTUAL)          do { if (::assert_success((ACTUAL),             #ACTUAL)) { return false; } } while (0);
 #define ASSERT_ERROR(ACTUAL, EXPECTED)  do { if (!::assert_error  ((ACTUAL), (EXPECTED), #ACTUAL)) { return false; } } while (0);
 #define ASSERT_TRUE(ACTUAL)             do { if (!::assert_true   ((ACTUAL),             #ACTUAL)) { return false; } } while (0);