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-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 4.0.3
+    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         = "4.0.3"
+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.
@@ -120,7 +121,6 @@ Some users may want to browse code along with the compiled assembly. You want to
 * [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)
- 
 
 Performance results
 -------------------

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/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

@@ -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"]`.
@@ -1400,6 +1400,42 @@ maps it to parsing code. We call the default constructor,
 and then assign values to the public members.
 
 
+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
@@ -1456,7 +1492,7 @@ The code might be as simple as the following.
 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

@@ -34,12 +34,13 @@ 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 writing the content, if you have reasons to believe that the content might violate UTF-8 conventions, you can check it as follows:
 
@@ -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/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>
@@ -109,7 +111,7 @@ 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>
@@ -119,7 +121,7 @@ inline auto to_adaptor<T>::operator()(ondemand::parser &parser, padded_string_vi
 
 template <typename T>
 inline auto to_adaptor<T>::operator()(std::string str) const noexcept {
-  return auto_parser{pad_with_reserve(str)};
+  return auto_parser<ondemand::parser *>{pad_with_reserve(str)};
 }
 
 template <typename T>

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>);
@@ -78,6 +81,8 @@ struct to_adaptor {
 	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

@@ -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 +285,11 @@ simdjson_inline void string_builder::clear() noexcept {
 
 namespace internal {
 
-
 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 int_log2(number_type x) {
+  return 63 - leading_zeroes(uint64_t(x) | 1);
+}
 
 simdjson_really_inline int fast_digit_count_32(uint32_t x) {
   static uint64_t table[] = {
@@ -301,7 +303,6 @@ simdjson_really_inline int fast_digit_count_32(uint32_t x) {
   return uint32_t((x + table[int_log2(x)]) >> 32);
 }
 
-
 simdjson_really_inline int fast_digit_count_64(uint64_t x) {
   static uint64_t table[] = {9,
                              99,
@@ -335,28 +336,29 @@ simdjson_really_inline size_t digit_count(number_type v) noexcept {
                 "We only support 8-bit, 16-bit, 32-bit and 64-bit numbers");
   SIMDJSON_IF_CONSTEXPR(sizeof(number_type) <= 4) {
     return fast_digit_count_32(static_cast<uint32_t>(v));
-  } else {
+  }
+  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
 
@@ -392,7 +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;
       }
@@ -419,7 +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;
       }
@@ -471,10 +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);
@@ -499,6 +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);
@@ -506,18 +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);
@@ -534,8 +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 {
@@ -551,11 +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();
-
   }
 }
 
@@ -563,7 +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
@@ -592,70 +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;
 
@@ -248,7 +239,6 @@ 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;
 
@@ -274,7 +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>
@@ -286,18 +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)) {
       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

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
@@ -217,7 +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.
@@ -738,7 +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 "4.0.3"
+#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 = 3
+  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/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

@@ -62,57 +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"( {
@@ -130,22 +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
@@ -211,7 +252,7 @@ bool simple() {
   }
 
 
-#endif
+#endif // SIMDJSON_STATIC_REFLECTION
 bool broken() {
   TEST_START();
   simdjson::padded_string short_json_cars = R"( { "make )"_padded;
@@ -428,15 +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();
 }
@@ -465,8 +497,11 @@ bool test_to_vs_from_equivalence() {
 #endif // SIMDJSON_EXCEPTIONS
 bool run() {
   return
-#if SIMDJSON_STATIC_REFLECTION
-      meeting_time_test() && meeting_test() && 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);