v0.9.6

This would prevent cloning plus has better performance when pushing values to Lua stack (`IntoLua::push_into_stack` method)

CHANGELOG.md

@@ -1,3 +1,19 @@
+## v0.9.6
+
+- Added `to_pointer` function to `Function`/`Table`/`Thread`
+- Implemented `IntoLua` for `&Value`
+- Implemented `FromLua` for `RegistryKey`
+- Faster (~5%) table array traversal during serialization
+- Some performance improvements for bool/int types
+
+## v0.9.5
+
+- Minimal Luau updated to 0.609
+- Luau max stack size increased to 1M (from 100K)
+- Implemented `IntoLua` for refs to `String`/`Table`/`Function`/`AnyUserData`/`Thread` + `RegistryKey`
+- Implemented `IntoLua` and `FromLua` for `OwnedThread`/`OwnedString`
+- Fixed `FromLua` derive proc macro to cover more cases
+
 ## v0.9.4
 
 - Fixed loading all-in-one modules under mixed states (eg. main state and coroutines)

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "mlua"
-version = "0.9.4" # remember to update mlua_derive
-authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@chucklefish.org>"]
+version = "0.9.6" # remember to update mlua_derive
+authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@kyju.org>"]
 rust-version = "1.71"
 edition = "2021"
 repository = "https://github.com/khvzak/mlua"
@@ -44,7 +44,7 @@ macros = ["mlua_derive/macros"]
 unstable = []
 
 [dependencies]
-mlua_derive = { version = "=0.9.1", optional = true, path = "mlua_derive" }
+mlua_derive = { version = "=0.9.2", optional = true, path = "mlua_derive" }
 bstr = { version = "1.0", features = ["std"], default_features = false }
 once_cell = { version = "1.0" }
 num-traits = { version = "0.2.14" }
@@ -55,7 +55,7 @@ erased-serde = { version = "0.4", optional = true }
 serde-value = { version = "0.7", optional = true }
 parking_lot = { version = "0.12", optional = true }
 
-ffi = { package = "mlua-sys", version = "0.5.0", path = "mlua-sys" }
+ffi = { package = "mlua-sys", version = "0.5.1", path = "mlua-sys" }
 
 [target.'cfg(unix)'.dependencies]
 libloading = { version = "0.8", optional = true }

README.md

@@ -7,8 +7,8 @@
 [crates.io]: https://crates.io/crates/mlua
 [API Documentation]: https://docs.rs/mlua/badge.svg
 [docs.rs]: https://docs.rs/mlua
-[Coverage Status]: https://codecov.io/gh/khvzak/mlua/branch/master/graph/badge.svg?token=99339FS1CG
-[codecov.io]: https://codecov.io/gh/khvzak/mlua
+[Coverage Status]: https://codecov.io/gh/mlua-rs/mlua/branch/master/graph/badge.svg?token=99339FS1CG
+[codecov.io]: https://codecov.io/gh/mlua-rs/mlua
 [MSRV]: https://img.shields.io/badge/rust-1.71+-brightgreen.svg?&logo=rust
 
 [Guided Tour] | [Benchmarks] | [FAQ]

benches/benchmark.rs

@@ -1,5 +1,7 @@
-use criterion::{criterion_group, criterion_main, BatchSize, Criterion};
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::time::Duration;
+
+use criterion::{criterion_group, criterion_main, BatchSize, Criterion};
 use tokio::runtime::Runtime;
 use tokio::task;
 
@@ -10,10 +12,10 @@ fn collect_gc_twice(lua: &Lua) {
     lua.gc_collect().unwrap();
 }
 
-fn create_table(c: &mut Criterion) {
+fn table_create_empty(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("create [table empty]", |b| {
+    c.bench_function("table [create empty]", |b| {
         b.iter_batched(
             || collect_gc_twice(&lua),
             |_| {
@@ -24,35 +26,33 @@ fn create_table(c: &mut Criterion) {
     });
 }
 
-fn create_array(c: &mut Criterion) {
+fn table_create_array(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("create [array] 10", |b| {
+    c.bench_function("table [create array]", |b| {
         b.iter_batched(
             || collect_gc_twice(&lua),
             |_| {
-                let table = lua.create_table().unwrap();
-                for i in 1..=10 {
-                    table.set(i, i).unwrap();
-                }
+                lua.create_sequence_from(1..=10).unwrap();
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn create_string_table(c: &mut Criterion) {
+fn table_create_hash(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("create [table string] 10", |b| {
+    c.bench_function("table [create hash]", |b| {
         b.iter_batched(
             || collect_gc_twice(&lua),
             |_| {
-                let table = lua.create_table().unwrap();
-                for &s in &["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"] {
-                    let s = lua.create_string(s).unwrap();
-                    table.set(s.clone(), s).unwrap();
-                }
+                lua.create_table_from(
+                    ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
+                        .into_iter()
+                        .map(|s| (s, s)),
+                )
+                .unwrap();
             },
             BatchSize::SmallInput,
         );
@@ -62,17 +62,15 @@ fn create_string_table(c: &mut Criterion) {
 fn table_get_set(c: &mut Criterion) {
     let lua = Lua::new();
 
-    let table = lua.create_table().unwrap();
-
-    c.bench_function("table raw_get and raw_set [10]", |b| {
+    c.bench_function("table [get and set]", |b| {
         b.iter_batched(
             || {
                 collect_gc_twice(&lua);
-                table.clear().unwrap();
+                lua.create_table().unwrap()
             },
-            |_| {
-                for (i, &s) in ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"]
-                    .iter()
+            |table| {
+                for (i, s) in ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"]
+                    .into_iter()
                     .enumerate()
                 {
                     table.raw_set(s, i).unwrap();
@@ -87,7 +85,7 @@ fn table_get_set(c: &mut Criterion) {
 fn table_traversal_pairs(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("table traversal [pairs]", |b| {
+    c.bench_function("table [traversal pairs]", |b| {
         b.iter_batched(
             || lua.globals(),
             |globals| {
@@ -103,7 +101,7 @@ fn table_traversal_pairs(c: &mut Criterion) {
 fn table_traversal_for_each(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("table traversal [for_each]", |b| {
+    c.bench_function("table [traversal for_each]", |b| {
         b.iter_batched(
             || lua.globals(),
             |globals| globals.for_each::<String, LuaValue>(|_k, _v| Ok(())),
@@ -117,7 +115,7 @@ fn table_traversal_sequence(c: &mut Criterion) {
 
     let table = lua.create_sequence_from(1..1000).unwrap();
 
-    c.bench_function("table traversal [sequence]", |b| {
+    c.bench_function("table [traversal sequence]", |b| {
         b.iter_batched(
             || table.clone(),
             |table| {
@@ -130,236 +128,255 @@ fn table_traversal_sequence(c: &mut Criterion) {
     });
 }
 
-fn create_function(c: &mut Criterion) {
+fn function_create(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("create [function] 10", |b| {
+    c.bench_function("function [create Rust]", |b| {
         b.iter_batched(
             || collect_gc_twice(&lua),
             |_| {
-                for i in 0..10 {
-                    lua.create_function(move |_, ()| Ok(i)).unwrap();
-                }
+                lua.create_function(|_, ()| Ok(123)).unwrap();
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn call_lua_function(c: &mut Criterion) {
+fn function_call_sum(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("call Lua function [sum] 3 10", |b| {
-        b.iter_batched_ref(
-            || {
-                collect_gc_twice(&lua);
-                lua.load("function(a, b, c) return a + b + c end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
-            },
-            |function| {
-                for i in 0..10 {
-                    let _result: i64 = function.call((i, i + 1, i + 2)).unwrap();
-                }
-            },
-            BatchSize::SmallInput,
-        );
-    });
-}
-
-fn call_sum_callback(c: &mut Criterion) {
-    let lua = Lua::new();
-    let callback = lua
-        .create_function(|_, (a, b, c): (i64, i64, i64)| Ok(a + b + c))
+    let sum = lua
+        .create_function(|_, (a, b, c): (i64, i64, i64)| Ok(a + b - c))
         .unwrap();
-    lua.globals().set("callback", callback).unwrap();
 
-    c.bench_function("call Rust callback [sum] 3 10", |b| {
-        b.iter_batched_ref(
-            || {
-                collect_gc_twice(&lua);
-                lua.load("function() for i = 1,10 do callback(i, i+1, i+2) end end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
-            },
-            |function| {
-                function.call::<_, ()>(()).unwrap();
+    c.bench_function("function [call Rust sum]", |b| {
+        b.iter_batched(
+            || collect_gc_twice(&lua),
+            |_| {
+                assert_eq!(sum.call::<_, i64>((10, 20, 30)).unwrap(), 0);
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn call_async_sum_callback(c: &mut Criterion) {
-    let options = LuaOptions::new().thread_pool_size(1024);
-    let lua = Lua::new_with(LuaStdLib::ALL_SAFE, options).unwrap();
-    let callback = lua
-        .create_async_function(|_, (a, b, c): (i64, i64, i64)| async move {
-            task::yield_now().await;
-            Ok(a + b + c)
-        })
-        .unwrap();
-    lua.globals().set("callback", callback).unwrap();
-
-    c.bench_function("call async Rust callback [sum] 3 10", |b| {
-        let rt = Runtime::new().unwrap();
-        b.to_async(rt).iter_batched(
-            || {
-                collect_gc_twice(&lua);
-                lua.load("function() for i = 1,10 do callback(i, i+1, i+2) end end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
-            },
-            |function| async move {
-                function.call_async::<_, ()>(()).await.unwrap();
-            },
-            BatchSize::SmallInput,
-        );
-    });
-}
-
-fn call_concat_callback(c: &mut Criterion) {
+fn function_call_lua_sum(c: &mut Criterion) {
     let lua = Lua::new();
-    let callback = lua
+
+    let sum = lua
+        .load("function(a, b, c) return a + b - c end")
+        .eval::<LuaFunction>()
+        .unwrap();
+
+    c.bench_function("function [call Lua sum]", |b| {
+        b.iter_batched(
+            || collect_gc_twice(&lua),
+            |_| {
+                assert_eq!(sum.call::<_, i64>((10, 20, 30)).unwrap(), 0);
+            },
+            BatchSize::SmallInput,
+        );
+    });
+}
+
+fn function_call_concat(c: &mut Criterion) {
+    let lua = Lua::new();
+
+    let concat = lua
         .create_function(|_, (a, b): (LuaString, LuaString)| {
             Ok(format!("{}{}", a.to_str()?, b.to_str()?))
         })
         .unwrap();
-    lua.globals().set("callback", callback).unwrap();
+    let i = AtomicUsize::new(0);
 
-    c.bench_function("call Rust callback [concat string] 10", |b| {
-        b.iter_batched_ref(
+    c.bench_function("function [call Rust concat string]", |b| {
+        b.iter_batched(
             || {
                 collect_gc_twice(&lua);
-                lua.load("function() for i = 1,10 do callback('a', tostring(i)) end end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
+                i.fetch_add(1, Ordering::Relaxed)
             },
-            |function| {
-                function.call::<_, ()>(()).unwrap();
+            |i| {
+                assert_eq!(
+                    concat.call::<_, LuaString>(("num:", i)).unwrap(),
+                    format!("num:{i}")
+                );
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn create_registry_values(c: &mut Criterion) {
+fn function_call_lua_concat(c: &mut Criterion) {
     let lua = Lua::new();
 
-    c.bench_function("create [registry value] 10", |b| {
+    let concat = lua
+        .load("function(a, b) return a..b end")
+        .eval::<LuaFunction>()
+        .unwrap();
+    let i = AtomicUsize::new(0);
+
+    c.bench_function("function [call Lua concat string]", |b| {
         b.iter_batched(
-            || collect_gc_twice(&lua),
-            |_| {
-                for _ in 0..10 {
-                    lua.create_registry_value(lua.pack(true).unwrap()).unwrap();
-                }
-                lua.expire_registry_values();
+            || {
+                collect_gc_twice(&lua);
+                i.fetch_add(1, Ordering::Relaxed)
+            },
+            |i| {
+                assert_eq!(
+                    concat.call::<_, LuaString>(("num:", i)).unwrap(),
+                    format!("num:{i}")
+                );
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn create_userdata(c: &mut Criterion) {
+fn function_async_call_sum(c: &mut Criterion) {
+    let options = LuaOptions::new().thread_pool_size(1024);
+    let lua = Lua::new_with(LuaStdLib::ALL_SAFE, options).unwrap();
+
+    let sum = lua
+        .create_async_function(|_, (a, b, c): (i64, i64, i64)| async move {
+            task::yield_now().await;
+            Ok(a + b - c)
+        })
+        .unwrap();
+
+    c.bench_function("function [async call Rust sum]", |b| {
+        let rt = Runtime::new().unwrap();
+        b.to_async(rt).iter_batched(
+            || collect_gc_twice(&lua),
+            |_| async {
+                assert_eq!(sum.call_async::<_, i64>((10, 20, 30)).await.unwrap(), 0);
+            },
+            BatchSize::SmallInput,
+        );
+    });
+}
+
+fn registry_value_create(c: &mut Criterion) {
+    let lua = Lua::new();
+    lua.gc_stop();
+
+    c.bench_function("registry value [create]", |b| {
+        b.iter_batched(
+            || collect_gc_twice(&lua),
+            |_| lua.create_registry_value("hello").unwrap(),
+            BatchSize::SmallInput,
+        );
+    });
+}
+
+fn userdata_create(c: &mut Criterion) {
     struct UserData(i64);
     impl LuaUserData for UserData {}
 
     let lua = Lua::new();
 
-    c.bench_function("create [table userdata] 10", |b| {
+    c.bench_function("userdata [create]", |b| {
         b.iter_batched(
             || collect_gc_twice(&lua),
             |_| {
-                let table: LuaTable = lua.create_table().unwrap();
-                for i in 1..11 {
-                    table.set(i, UserData(i)).unwrap();
-                }
+                lua.create_userdata(UserData(123)).unwrap();
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn call_userdata_index(c: &mut Criterion) {
+fn userdata_call_index(c: &mut Criterion) {
     struct UserData(i64);
     impl LuaUserData for UserData {
         fn add_methods<'lua, M: LuaUserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_meta_method(LuaMetaMethod::Index, move |_, _, index: String| Ok(index));
+            methods.add_meta_method(LuaMetaMethod::Index, move |_, _, key: LuaString| Ok(key));
         }
     }
 
     let lua = Lua::new();
-    lua.globals().set("userdata", UserData(10)).unwrap();
+    let ud = lua.create_userdata(UserData(123)).unwrap();
+    let index = lua
+        .load("function(ud) return ud.test end")
+        .eval::<LuaFunction>()
+        .unwrap();
 
-    c.bench_function("call [userdata index] 10", |b| {
-        b.iter_batched_ref(
-            || {
-                collect_gc_twice(&lua);
-                lua.load("function() for i = 1,10 do local v = userdata.test end end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
-            },
-            |function| {
-                function.call::<_, ()>(()).unwrap();
+    c.bench_function("userdata [call index]", |b| {
+        b.iter_batched(
+            || collect_gc_twice(&lua),
+            |_| {
+                assert_eq!(index.call::<_, LuaString>(&ud).unwrap(), "test");
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn call_userdata_method(c: &mut Criterion) {
+fn userdata_call_method(c: &mut Criterion) {
     struct UserData(i64);
     impl LuaUserData for UserData {
         fn add_methods<'lua, M: LuaUserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_method("method", |_, this, ()| Ok(this.0));
+            methods.add_method("add", |_, this, i: i64| Ok(this.0 + i));
         }
     }
 
     let lua = Lua::new();
-    lua.globals().set("userdata", UserData(10)).unwrap();
+    let ud = lua.create_userdata(UserData(123)).unwrap();
+    let method = lua
+        .load("function(ud, i) return ud:add(i) end")
+        .eval::<LuaFunction>()
+        .unwrap();
+    let i = AtomicUsize::new(0);
 
-    c.bench_function("call [userdata method] 10", |b| {
-        b.iter_batched_ref(
+    c.bench_function("userdata [call method]", |b| {
+        b.iter_batched(
             || {
                 collect_gc_twice(&lua);
-                lua.load("function() for i = 1,10 do userdata:method() end end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
+                i.fetch_add(1, Ordering::Relaxed)
             },
-            |function| {
-                function.call::<_, ()>(()).unwrap();
+            |i| {
+                assert_eq!(method.call::<_, usize>((&ud, i)).unwrap(), 123 + i);
             },
             BatchSize::SmallInput,
         );
     });
 }
 
-fn call_async_userdata_method(c: &mut Criterion) {
-    struct UserData(String);
-
+fn userdata_async_call_method(c: &mut Criterion) {
+    struct UserData(i64);
     impl LuaUserData for UserData {
         fn add_methods<'lua, M: LuaUserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_async_method("method", |_, this, ()| async move { Ok(this.0.clone()) });
+            methods.add_async_method("add", |_, this, i: i64| async move {
+                task::yield_now().await;
+                Ok(this.0 + i)
+            });
         }
     }
 
     let options = LuaOptions::new().thread_pool_size(1024);
     let lua = Lua::new_with(LuaStdLib::ALL_SAFE, options).unwrap();
-    lua.globals()
-        .set("userdata", UserData("hello".to_string()))
+    let ud = lua.create_userdata(UserData(123)).unwrap();
+    let method = lua
+        .load("function(ud, i) return ud:add(i) end")
+        .eval::<LuaFunction>()
         .unwrap();
+    let i = AtomicUsize::new(0);
 
-    c.bench_function("call async [userdata method] 10", |b| {
+    c.bench_function("userdata [async call method] 10", |b| {
         let rt = Runtime::new().unwrap();
         b.to_async(rt).iter_batched(
             || {
                 collect_gc_twice(&lua);
-                lua.load("function() for i = 1,10 do userdata:method() end end")
-                    .eval::<LuaFunction>()
-                    .unwrap()
+                (
+                    method.clone(),
+                    ud.clone(),
+                    i.fetch_add(1, Ordering::Relaxed),
+                )
             },
-            |function| async move {
-                function.call_async::<_, ()>(()).await.unwrap();
+            |(method, ud, i)| async move {
+                assert_eq!(
+                    method.call_async::<_, usize>((ud, i)).await.unwrap(),
+                    123 + i
+                );
             },
             BatchSize::SmallInput,
         );
@@ -369,27 +386,31 @@ fn call_async_userdata_method(c: &mut Criterion) {
 criterion_group! {
     name = benches;
     config = Criterion::default()
-        .sample_size(300)
+        .sample_size(500)
         .measurement_time(Duration::from_secs(10))
         .noise_threshold(0.02);
     targets =
-        create_table,
-        create_array,
-        create_string_table,
+        table_create_empty,
+        table_create_array,
+        table_create_hash,
         table_get_set,
         table_traversal_pairs,
         table_traversal_for_each,
         table_traversal_sequence,
-        create_function,
-        call_lua_function,
-        call_sum_callback,
-        call_async_sum_callback,
-        call_concat_callback,
-        create_registry_values,
-        create_userdata,
-        call_userdata_index,
-        call_userdata_method,
-        call_async_userdata_method,
+
+        function_create,
+        function_call_sum,
+        function_call_lua_sum,
+        function_call_concat,
+        function_call_lua_concat,
+        function_async_call_sum,
+
+        registry_value_create,
+
+        userdata_create,
+        userdata_call_index,
+        userdata_call_method,
+        userdata_async_call_method,
 }
 
 criterion_main!(benches);

benches/serde.rs

@@ -8,43 +8,35 @@ fn collect_gc_twice(lua: &Lua) {
     lua.gc_collect().unwrap();
 }
 
-fn serialize_json(c: &mut Criterion) {
+fn encode_json(c: &mut Criterion) {
     let lua = Lua::new();
 
-    lua.globals()
-        .set(
-            "encode",
-            LuaFunction::wrap(|_, t: LuaValue| Ok(serde_json::to_string(&t).unwrap())),
+    let encode = lua
+        .create_function(|_, t: LuaValue| Ok(serde_json::to_string(&t).unwrap()))
+        .unwrap();
+    let table = lua
+        .load(
+            r#"{
+        name = "Clark Kent",
+        address = {
+            city = "Smallville",
+            state = "Kansas",
+            country = "USA",
+        },
+        age = 22,
+        parents = {"Jonathan Kent", "Martha Kent"},
+        superman = true,
+        interests = {"flying", "saving the world", "kryptonite"},
+    }"#,
         )
+        .eval::<LuaTable>()
         .unwrap();
 
-    c.bench_function("serialize table to json [10]", |b| {
+    c.bench_function("serialize json", |b| {
         b.iter_batched(
-            || {
-                collect_gc_twice(&lua);
-                lua.load(
-                    r#"
-                local encode = encode
-                return function()
-                    for i = 1, 10 do
-                        encode({
-                            name = "Clark Kent",
-                            nickname = "Superman",
-                            address = {
-                                city = "Metropolis",
-                            },
-                            age = 32,
-                            superman = true,
-                        })
-                    end
-                end
-            "#,
-                )
-                .eval::<LuaFunction>()
-                .unwrap()
-            },
-            |func| {
-                func.call::<_, ()>(()).unwrap();
+            || collect_gc_twice(&lua),
+            |_| {
+                encode.call::<_, LuaString>(&table).unwrap();
             },
             BatchSize::SmallInput,
         );
@@ -54,11 +46,11 @@ fn serialize_json(c: &mut Criterion) {
 criterion_group! {
     name = benches;
     config = Criterion::default()
-        .sample_size(300)
+        .sample_size(500)
         .measurement_time(Duration::from_secs(10))
         .noise_threshold(0.02);
     targets =
-        serialize_json,
+        encode_json,
 }
 
 criterion_main!(benches);

examples/guided_tour.rs

@@ -24,7 +24,7 @@ fn main() -> Result<()> {
 
     // You can load and evaluate Lua code. The returned type of `Lua::load` is a builder
     // that allows you to change settings before running Lua code. Here, we are using it to set
-    // the name of the laoded chunk to "example code", which will be used when Lua error
+    // the name of the loaded chunk to "example code", which will be used when Lua error
     // messages are printed.
 
     lua.load(
@@ -89,7 +89,7 @@ fn main() -> Result<()> {
     let print: Function = globals.get("print")?;
     print.call::<_, ()>("hello from rust")?;
 
-    // This API generally handles variadics using tuples. This is one way to call a function with
+    // This API generally handles variadic using tuples. This is one way to call a function with
     // multiple parameters:
 
     print.call::<_, ()>(("hello", "again", "from", "rust"))?;
@@ -100,7 +100,7 @@ fn main() -> Result<()> {
         ["hello", "yet", "again", "from", "rust"].iter().cloned(),
     ))?;
 
-    // You can bind rust functions to Lua as well. Callbacks receive the Lua state inself as their
+    // You can bind rust functions to Lua as well. Callbacks receive the Lua state itself as their
     // first parameter, and the arguments given to the function as the second parameter. The type
     // of the arguments can be anything that is convertible from the parameters given by Lua, in
     // this case, the function expects two string sequences.

mlua-sys/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua-sys"
-version = "0.5.0"
+version = "0.5.1"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
 rust-version = "1.71"
 edition = "2021"
@@ -40,4 +40,4 @@ cfg-if = "1.0"
 pkg-config = "0.3.17"
 lua-src = { version = ">= 546.0.2, < 546.1.0", optional = true }
 luajit-src = { version = ">= 210.5.0, < 210.6.0", optional = true }
-luau0-src = { version = "0.7.11", optional = true }
+luau0-src = { version = "0.8.0", optional = true }

mlua-sys/build/find_vendored.rs

@@ -21,6 +21,7 @@ pub fn probe_lua() {
     #[cfg(feature = "luau")]
     let artifacts = luau0_src::Build::new()
         .enable_codegen(cfg!(feature = "luau-codegen"))
+        .set_max_cstack_size(1000000)
         .set_vector_size(if cfg!(feature = "luau-vector4") { 4 } else { 3 })
         .build();
 

mlua-sys/src/lua51/lua.rs

@@ -328,6 +328,14 @@ pub unsafe fn lua_getglobal_(L: *mut lua_State, var: *const c_char) {
     lua_getfield_(L, LUA_GLOBALSINDEX, var)
 }
 
+#[inline(always)]
+pub unsafe fn lua_tolightuserdata(L: *mut lua_State, idx: c_int) -> *mut c_void {
+    if lua_islightuserdata(L, idx) != 0 {
+        return lua_touserdata(L, idx);
+    }
+    ptr::null_mut()
+}
+
 #[inline(always)]
 pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
     lua_tolstring(L, i, ptr::null_mut())

mlua-sys/src/lua52/lua.rs

@@ -417,6 +417,14 @@ pub unsafe fn lua_pushglobaltable(L: *mut lua_State) {
     lua_rawgeti_(L, LUA_REGISTRYINDEX, LUA_RIDX_GLOBALS as _)
 }
 
+#[inline(always)]
+pub unsafe fn lua_tolightuserdata(L: *mut lua_State, idx: c_int) -> *mut c_void {
+    if lua_islightuserdata(L, idx) != 0 {
+        return lua_touserdata(L, idx);
+    }
+    ptr::null_mut()
+}
+
 #[inline(always)]
 pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
     lua_tolstring(L, i, ptr::null_mut())

mlua-sys/src/lua53/lua.rs

@@ -424,6 +424,14 @@ pub unsafe fn lua_pushglobaltable(L: *mut lua_State) -> c_int {
     lua_rawgeti(L, LUA_REGISTRYINDEX, LUA_RIDX_GLOBALS)
 }
 
+#[inline(always)]
+pub unsafe fn lua_tolightuserdata(L: *mut lua_State, idx: c_int) -> *mut c_void {
+    if lua_islightuserdata(L, idx) != 0 {
+        return lua_touserdata(L, idx);
+    }
+    ptr::null_mut()
+}
+
 #[inline(always)]
 pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
     lua_tolstring(L, i, ptr::null_mut())

mlua-sys/src/lua54/lua.rs

@@ -457,6 +457,14 @@ pub unsafe fn lua_pushglobaltable(L: *mut lua_State) -> c_int {
     lua_rawgeti(L, LUA_REGISTRYINDEX, LUA_RIDX_GLOBALS)
 }
 
+#[inline(always)]
+pub unsafe fn lua_tolightuserdata(L: *mut lua_State, idx: c_int) -> *mut c_void {
+    if lua_islightuserdata(L, idx) != 0 {
+        return lua_touserdata(L, idx);
+    }
+    ptr::null_mut()
+}
+
 #[inline(always)]
 pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
     lua_tolstring(L, i, ptr::null_mut())

mlua-sys/src/luau/lauxlib.rs

@@ -144,9 +144,12 @@ pub unsafe fn luaL_sandbox(L: *mut lua_State, enabled: c_int) {
 
     // set all builtin metatables to read-only
     lua_pushliteral(L, "");
-    lua_getmetatable(L, -1);
-    lua_setreadonly(L, -1, enabled);
-    lua_pop(L, 2);
+    if lua_getmetatable(L, -1) != 0 {
+        lua_setreadonly(L, -1, enabled);
+        lua_pop(L, 2);
+    } else {
+        lua_pop(L, 1);
+    }
 
     // set globals to readonly and activate safeenv since the env is immutable
     lua_setreadonly(L, LUA_GLOBALSINDEX, enabled);

mlua-sys/src/luau/lua.rs

@@ -8,7 +8,13 @@ use std::{mem, ptr};
 pub const LUA_MULTRET: c_int = -1;
 
 // Max number of Lua stack slots
-const LUAI_MAXCSTACK: c_int = 100000;
+const LUAI_MAXCSTACK: c_int = 1000000;
+
+// Number of valid Lua userdata tags
+const LUA_UTAG_LIMIT: c_int = 128;
+
+// Number of valid Lua lightuserdata tags
+const LUA_LUTAG_LIMIT: c_int = 128;
 
 //
 // Pseudo-indices
@@ -144,9 +150,11 @@ extern "C-unwind" {
     pub fn lua_objlen(L: *mut lua_State, idx: c_int) -> usize;
     pub fn lua_tocfunction(L: *mut lua_State, idx: c_int) -> Option<lua_CFunction>;
     pub fn lua_tolightuserdata(L: *mut lua_State, idx: c_int) -> *mut c_void;
+    pub fn lua_tolightuserdatatagged(L: *mut lua_State, idx: c_int, tag: c_int) -> *mut c_void;
     pub fn lua_touserdata(L: *mut lua_State, idx: c_int) -> *mut c_void;
     pub fn lua_touserdatatagged(L: *mut lua_State, idx: c_int, tag: c_int) -> *mut c_void;
     pub fn lua_userdatatag(L: *mut lua_State, idx: c_int) -> c_int;
+    pub fn lua_lightuserdatatag(L: *mut lua_State, idx: c_int) -> c_int;
     pub fn lua_tothread(L: *mut lua_State, idx: c_int) -> *mut lua_State;
     pub fn lua_tobuffer(L: *mut lua_State, idx: c_int, len: *mut usize) -> *mut c_void;
     pub fn lua_topointer(L: *mut lua_State, idx: c_int) -> *const c_void;
@@ -179,7 +187,7 @@ extern "C-unwind" {
     pub fn lua_pushboolean(L: *mut lua_State, b: c_int);
     pub fn lua_pushthread(L: *mut lua_State) -> c_int;
 
-    pub fn lua_pushlightuserdata(L: *mut lua_State, p: *mut c_void);
+    pub fn lua_pushlightuserdatatagged(L: *mut lua_State, p: *mut c_void, tag: c_int);
     pub fn lua_newuserdatatagged(L: *mut lua_State, sz: usize, tag: c_int) -> *mut c_void;
     pub fn lua_newuserdatadtor(L: *mut lua_State, sz: usize, dtor: lua_Udestructor) -> *mut c_void;
 
@@ -280,6 +288,8 @@ extern "C-unwind" {
     pub fn lua_setuserdatatag(L: *mut lua_State, idx: c_int, tag: c_int);
     pub fn lua_setuserdatadtor(L: *mut lua_State, tag: c_int, dtor: Option<lua_Destructor>);
     pub fn lua_getuserdatadtor(L: *mut lua_State, tag: c_int) -> Option<lua_Destructor>;
+    pub fn lua_setlightuserdataname(L: *mut lua_State, tag: c_int, name: *const c_char);
+    pub fn lua_getlightuserdataname(L: *mut lua_State, tag: c_int) -> *const c_char;
     pub fn lua_clonefunction(L: *mut lua_State, idx: c_int);
     pub fn lua_cleartable(L: *mut lua_State, idx: c_int);
     pub fn lua_getallocf(L: *mut lua_State, ud: *mut *mut c_void) -> lua_Alloc;
@@ -398,18 +408,22 @@ pub unsafe fn lua_pushliteral(L: *mut lua_State, s: &'static str) {
     lua_pushlstring_(L, c_str.as_ptr(), c_str.as_bytes().len())
 }
 
+#[inline(always)]
 pub unsafe fn lua_pushcfunction(L: *mut lua_State, f: lua_CFunction) {
     lua_pushcclosurek(L, f, ptr::null(), 0, None)
 }
 
+#[inline(always)]
 pub unsafe fn lua_pushcfunctiond(L: *mut lua_State, f: lua_CFunction, debugname: *const c_char) {
     lua_pushcclosurek(L, f, debugname, 0, None)
 }
 
+#[inline(always)]
 pub unsafe fn lua_pushcclosure(L: *mut lua_State, f: lua_CFunction, nup: c_int) {
     lua_pushcclosurek(L, f, ptr::null(), nup, None)
 }
 
+#[inline(always)]
 pub unsafe fn lua_pushcclosured(
     L: *mut lua_State,
     f: lua_CFunction,
@@ -419,6 +433,11 @@ pub unsafe fn lua_pushcclosured(
     lua_pushcclosurek(L, f, debugname, nup, None)
 }
 
+#[inline(always)]
+pub unsafe fn lua_pushlightuserdata(L: *mut lua_State, p: *mut c_void) {
+    lua_pushlightuserdatatagged(L, p, 0)
+}
+
 #[inline(always)]
 pub unsafe fn lua_setglobal(L: *mut lua_State, var: *const c_char) {
     lua_setfield(L, LUA_GLOBALSINDEX, var)

mlua_derive/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua_derive"
-version = "0.9.1"
+version = "0.9.2"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
 edition = "2021"
 description = "Procedural macros for the mlua crate."
@@ -19,6 +19,6 @@ quote = "1.0"
 proc-macro2 = { version = "1.0", features = ["span-locations"] }
 proc-macro-error = { version = "1.0", optional = true }
 syn = { version = "2.0", features = ["full"] }
-itertools = { version = "0.11", optional = true }
+itertools = { version = "0.12", optional = true }
 regex = { version = "1.4", optional = true }
 once_cell = { version = "1.0", optional = true }

mlua_derive/src/from_lua.rs

@@ -7,16 +7,17 @@ pub fn from_lua(input: TokenStream) -> TokenStream {
         ident, generics, ..
     } = parse_macro_input!(input as DeriveInput);
 
+    let ident_str = ident.to_string();
+    let (impl_generics, ty_generics, _) = generics.split_for_impl();
     let where_clause = match &generics.where_clause {
         Some(where_clause) => quote! { #where_clause, Self: 'static + Clone },
         None => quote! { where Self: 'static + Clone },
     };
-    let ident_str = ident.to_string();
 
     quote! {
-      impl #generics ::mlua::FromLua<'_> for #ident #generics #where_clause {
+      impl #impl_generics ::mlua::FromLua<'_> for #ident #ty_generics #where_clause {
         #[inline]
-        fn from_lua(value: ::mlua::Value<'_>, lua: &'_ ::mlua::Lua) -> ::mlua::Result<Self> {
+        fn from_lua(value: ::mlua::Value<'_>, _: &'_ ::mlua::Lua) -> ::mlua::Result<Self> {
           match value {
             ::mlua::Value::UserData(ud) => Ok(ud.borrow::<Self>()?.clone()),
             _ => Err(::mlua::Error::FromLuaConversionError {

src/conversion.rs

@@ -16,12 +16,15 @@ use crate::lua::Lua;
 use crate::string::String;
 use crate::table::Table;
 use crate::thread::Thread;
-use crate::types::{LightUserData, MaybeSend};
+use crate::types::{LightUserData, MaybeSend, RegistryKey};
 use crate::userdata::{AnyUserData, UserData, UserDataRef, UserDataRefMut};
 use crate::value::{FromLua, IntoLua, Nil, Value};
 
 #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
-use crate::{function::OwnedFunction, table::OwnedTable, userdata::OwnedAnyUserData};
+use crate::{
+    function::OwnedFunction, string::OwnedString, table::OwnedTable, thread::OwnedThread,
+    userdata::OwnedAnyUserData,
+};
 
 impl<'lua> IntoLua<'lua> for Value<'lua> {
     #[inline]
@@ -30,6 +33,18 @@ impl<'lua> IntoLua<'lua> for Value<'lua> {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &Value<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(self.clone())
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        lua.push_value_ref(self)
+    }
+}
+
 impl<'lua> FromLua<'lua> for Value<'lua> {
     #[inline]
     fn from_lua(lua_value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
@@ -44,6 +59,18 @@ impl<'lua> IntoLua<'lua> for String<'lua> {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &String<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::String(self.clone()))
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_ref(&self.0))
+    }
+}
+
 impl<'lua> FromLua<'lua> for String<'lua> {
     #[inline]
     fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<String<'lua>> {
@@ -57,6 +84,38 @@ impl<'lua> FromLua<'lua> for String<'lua> {
     }
 }
 
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for OwnedString {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::String(String(lua.adopt_owned_ref(self.0))))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for &OwnedString {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        OwnedString::into_lua(self.clone(), lua)
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_owned_ref(&self.0))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> FromLua<'lua> for OwnedString {
+    #[inline]
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<OwnedString> {
+        String::from_lua(value, lua).map(|s| s.into_owned())
+    }
+}
+
 impl<'lua> IntoLua<'lua> for Table<'lua> {
     #[inline]
     fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
@@ -64,6 +123,18 @@ impl<'lua> IntoLua<'lua> for Table<'lua> {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &Table<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Table(self.clone()))
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_ref(&self.0))
+    }
+}
+
 impl<'lua> FromLua<'lua> for Table<'lua> {
     #[inline]
     fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Table<'lua>> {
@@ -87,6 +158,20 @@ impl<'lua> IntoLua<'lua> for OwnedTable {
     }
 }
 
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for &OwnedTable {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        OwnedTable::into_lua(self.clone(), lua)
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_owned_ref(&self.0))
+    }
+}
+
 #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
 #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
 impl<'lua> FromLua<'lua> for OwnedTable {
@@ -103,6 +188,18 @@ impl<'lua> IntoLua<'lua> for Function<'lua> {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &Function<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Function(self.clone()))
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_ref(&self.0))
+    }
+}
+
 impl<'lua> FromLua<'lua> for Function<'lua> {
     #[inline]
     fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Function<'lua>> {
@@ -126,6 +223,20 @@ impl<'lua> IntoLua<'lua> for OwnedFunction {
     }
 }
 
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for &OwnedFunction {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        OwnedFunction::into_lua(self.clone(), lua)
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_owned_ref(&self.0))
+    }
+}
+
 #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
 #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
 impl<'lua> FromLua<'lua> for OwnedFunction {
@@ -142,6 +253,18 @@ impl<'lua> IntoLua<'lua> for Thread<'lua> {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &Thread<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Thread(self.clone()))
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_ref(&self.0))
+    }
+}
+
 impl<'lua> FromLua<'lua> for Thread<'lua> {
     #[inline]
     fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Thread<'lua>> {
@@ -156,6 +279,38 @@ impl<'lua> FromLua<'lua> for Thread<'lua> {
     }
 }
 
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for OwnedThread {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Thread(Thread(lua.adopt_owned_ref(self.0), self.1)))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for &OwnedThread {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        OwnedThread::into_lua(self.clone(), lua)
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_owned_ref(&self.0))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> FromLua<'lua> for OwnedThread {
+    #[inline]
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<OwnedThread> {
+        Thread::from_lua(value, lua).map(|s| s.into_owned())
+    }
+}
+
 impl<'lua> IntoLua<'lua> for AnyUserData<'lua> {
     #[inline]
     fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
@@ -163,6 +318,18 @@ impl<'lua> IntoLua<'lua> for AnyUserData<'lua> {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &AnyUserData<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::UserData(self.clone()))
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_ref(&self.0))
+    }
+}
+
 impl<'lua> FromLua<'lua> for AnyUserData<'lua> {
     #[inline]
     fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<AnyUserData<'lua>> {
@@ -189,6 +356,20 @@ impl<'lua> IntoLua<'lua> for OwnedAnyUserData {
     }
 }
 
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for &OwnedAnyUserData {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        OwnedAnyUserData::into_lua(self.clone(), lua)
+    }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        Ok(lua.push_owned_ref(&self.0))
+    }
+}
+
 #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
 #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
 impl<'lua> FromLua<'lua> for OwnedAnyUserData {
@@ -240,11 +421,44 @@ impl<'lua> FromLua<'lua> for Error {
     }
 }
 
+impl<'lua> IntoLua<'lua> for &RegistryKey {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        lua.registry_value(self)
+    }
+
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        if !lua.owns_registry_value(self) {
+            return Err(Error::MismatchedRegistryKey);
+        }
+
+        if self.is_nil() {
+            ffi::lua_pushnil(lua.state());
+        } else {
+            ffi::lua_rawgeti(lua.state(), ffi::LUA_REGISTRYINDEX, self.registry_id as _);
+        }
+        Ok(())
+    }
+}
+
+impl<'lua> FromLua<'lua> for RegistryKey {
+    #[inline]
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<RegistryKey> {
+        lua.create_registry_value(value)
+    }
+}
+
 impl<'lua> IntoLua<'lua> for bool {
     #[inline]
     fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Boolean(self))
     }
+
+    #[inline]
+    unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+        ffi::lua_pushboolean(lua.state(), self as c_int);
+        Ok(())
+    }
 }
 
 impl<'lua> FromLua<'lua> for bool {
@@ -256,6 +470,11 @@ impl<'lua> FromLua<'lua> for bool {
             _ => Ok(true),
         }
     }
+
+    #[inline]
+    unsafe fn from_stack(idx: c_int, lua: &'lua Lua) -> Result<Self> {
+        Ok(ffi::lua_toboolean(lua.state(), idx) != 0)
+    }
 }
 
 impl<'lua> IntoLua<'lua> for LightUserData {
@@ -497,6 +716,15 @@ macro_rules! lua_convert_int {
                         message: Some("out of range".to_owned()),
                     })
             }
+
+            #[inline]
+            unsafe fn push_into_stack(self, lua: &'lua Lua) -> Result<()> {
+                match cast(self) {
+                    Some(i) => ffi::lua_pushinteger(lua.state(), i),
+                    None => ffi::lua_pushnumber(lua.state(), self as ffi::lua_Number),
+                }
+                Ok(())
+            }
         }
 
         impl<'lua> FromLua<'lua> for $x {

src/function.rs

@@ -494,6 +494,16 @@ impl<'lua> Function<'lua> {
         }
     }
 
+    /// Converts this function to a generic C pointer.
+    ///
+    /// There is no way to convert the pointer back to its original value.
+    ///
+    /// Typically this function is used only for hashing and debug information.
+    #[inline]
+    pub fn to_pointer(&self) -> *const c_void {
+        self.0.to_pointer()
+    }
+
     /// Convert this handle to owned version.
     #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
     #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]

src/lua.rs

@@ -226,6 +226,7 @@ pub(crate) static EXTRA_REGISTRY_KEY: u8 = 0;
 
 const WRAPPED_FAILURE_POOL_SIZE: usize = 64;
 const MULTIVALUE_POOL_SIZE: usize = 64;
+const REF_STACK_RESERVE: c_int = 1;
 
 /// Requires `feature = "send"`
 #[cfg(feature = "send")]
@@ -519,8 +520,8 @@ impl Lua {
             #[cfg(feature = "module")]
             skip_memory_check: false,
             ref_thread,
-            // We need 1 extra stack space to move values in and out of the ref stack.
-            ref_stack_size: ffi::LUA_MINSTACK - 1,
+            // We need some reserved stack space to move values in and out of the ref stack.
+            ref_stack_size: ffi::LUA_MINSTACK - REF_STACK_RESERVE,
             ref_stack_top: ffi::lua_gettop(ref_thread),
             ref_free: Vec::new(),
             wrapped_failure_pool: Vec::with_capacity(WRAPPED_FAILURE_POOL_SIZE),
@@ -1413,8 +1414,8 @@ impl Lua {
             let protect = !self.unlikely_memory_error();
             push_table(state, 0, lower_bound, protect)?;
             for (k, v) in iter {
-                self.push_value(k.into_lua(self)?)?;
-                self.push_value(v.into_lua(self)?)?;
+                self.push(k)?;
+                self.push(v)?;
                 if protect {
                     protect_lua!(state, 3, 1, fn(state) ffi::lua_rawset(state, -3))?;
                 } else {
@@ -1442,7 +1443,7 @@ impl Lua {
             let protect = !self.unlikely_memory_error();
             push_table(state, lower_bound, 0, protect)?;
             for (i, v) in iter.enumerate() {
-                self.push_value(v.into_lua(self)?)?;
+                self.push(v)?;
                 if protect {
                     protect_lua!(state, 2, 1, |state| {
                         ffi::lua_rawseti(state, -2, (i + 1) as Integer);
@@ -1977,12 +1978,11 @@ impl Lua {
         T: IntoLua<'lua>,
     {
         let state = self.state();
-        let t = t.into_lua(self)?;
         unsafe {
             let _sg = StackGuard::new(state);
             check_stack(state, 5)?;
 
-            self.push_value(t)?;
+            self.push(t)?;
             rawset_field(state, ffi::LUA_REGISTRYINDEX, name)
         }
     }
@@ -2269,33 +2269,38 @@ impl Lua {
         extra.app_data.remove()
     }
 
-    /// Pushes a value onto the Lua stack.
+    /// Pushes a value that implements `IntoLua` onto the Lua stack.
+    ///
+    /// Uses 2 stack spaces, does not call checkstack.
+    #[doc(hidden)]
+    #[inline(always)]
+    pub unsafe fn push<'lua>(&'lua self, value: impl IntoLua<'lua>) -> Result<()> {
+        value.push_into_stack(self)
+    }
+
+    /// Pushes a `Value` onto the Lua stack.
     ///
     /// Uses 2 stack spaces, does not call checkstack.
     #[doc(hidden)]
     pub unsafe fn push_value(&self, value: Value) -> Result<()> {
+        if let Value::Error(err) = value {
+            let protect = !self.unlikely_memory_error();
+            return push_gc_userdata(self.state(), WrappedFailure::Error(err), protect);
+        }
+        self.push_value_ref(&value)
+    }
+
+    /// Pushes a `&Value` (by reference) onto the Lua stack.
+    ///
+    /// Similar to [`Lua::push_value`], uses 2 stack spaces, does not call checkstack.
+    pub(crate) unsafe fn push_value_ref(&self, value: &Value) -> Result<()> {
         let state = self.state();
         match value {
-            Value::Nil => {
-                ffi::lua_pushnil(state);
-            }
-
-            Value::Boolean(b) => {
-                ffi::lua_pushboolean(state, b as c_int);
-            }
-
-            Value::LightUserData(ud) => {
-                ffi::lua_pushlightuserdata(state, ud.0);
-            }
-
-            Value::Integer(i) => {
-                ffi::lua_pushinteger(state, i);
-            }
-
-            Value::Number(n) => {
-                ffi::lua_pushnumber(state, n);
-            }
-
+            Value::Nil => ffi::lua_pushnil(state),
+            Value::Boolean(b) => ffi::lua_pushboolean(state, *b as c_int),
+            Value::LightUserData(ud) => ffi::lua_pushlightuserdata(state, ud.0),
+            Value::Integer(i) => ffi::lua_pushinteger(state, *i),
+            Value::Number(n) => ffi::lua_pushnumber(state, *n),
             #[cfg(feature = "luau")]
             Value::Vector(v) => {
                 #[cfg(not(feature = "luau-vector4"))]
@@ -2303,33 +2308,16 @@ impl Lua {
                 #[cfg(feature = "luau-vector4")]
                 ffi::lua_pushvector(state, v.x(), v.y(), v.z(), v.w());
             }
-
-            Value::String(s) => {
-                self.push_ref(&s.0);
-            }
-
-            Value::Table(t) => {
-                self.push_ref(&t.0);
-            }
-
-            Value::Function(f) => {
-                self.push_ref(&f.0);
-            }
-
-            Value::Thread(t) => {
-                self.push_ref(&t.0);
-            }
-
-            Value::UserData(ud) => {
-                self.push_ref(&ud.0);
-            }
-
+            Value::String(s) => self.push_ref(&s.0),
+            Value::Table(t) => self.push_ref(&t.0),
+            Value::Function(f) => self.push_ref(&f.0),
+            Value::Thread(t) => self.push_ref(&t.0),
+            Value::UserData(ud) => self.push_ref(&ud.0),
             Value::Error(err) => {
                 let protect = !self.unlikely_memory_error();
-                push_gc_userdata(state, WrappedFailure::Error(err), protect)?;
+                push_gc_userdata(state, WrappedFailure::Error(err.clone()), protect)?;
             }
         }
-
         Ok(())
     }
 
@@ -2558,6 +2546,15 @@ impl Lua {
         ffi::lua_xpush(self.ref_thread(), self.state(), lref.index);
     }
 
+    #[cfg(all(feature = "unstable", not(feature = "send")))]
+    pub(crate) unsafe fn push_owned_ref(&self, loref: &crate::types::LuaOwnedRef) {
+        assert!(
+            Arc::ptr_eq(&loref.inner, &self.0),
+            "Lua instance passed Value created from a different main Lua state"
+        );
+        ffi::lua_xpush(self.ref_thread(), self.state(), loref.index);
+    }
+
     // Pops the topmost element of the stack and stores a reference to it. This pins the object,
     // preventing garbage collection until the returned `LuaRef` is dropped.
     //
@@ -2634,12 +2631,12 @@ impl Lua {
         let metatable_nrec = metatable_nrec + registry.async_meta_methods.len();
         push_table(state, 0, metatable_nrec, true)?;
         for (k, m) in registry.meta_methods {
-            self.push_value(Value::Function(self.create_callback(m)?))?;
+            self.push(self.create_callback(m)?)?;
             rawset_field(state, -2, MetaMethod::validate(&k)?)?;
         }
         #[cfg(feature = "async")]
         for (k, m) in registry.async_meta_methods {
-            self.push_value(Value::Function(self.create_async_callback(m)?))?;
+            self.push(self.create_async_callback(m)?)?;
             rawset_field(state, -2, MetaMethod::validate(&k)?)?;
         }
         let mut has_name = false;
@@ -2690,7 +2687,7 @@ impl Lua {
         if field_getters_nrec > 0 {
             push_table(state, 0, field_getters_nrec, true)?;
             for (k, m) in registry.field_getters {
-                self.push_value(Value::Function(self.create_callback(m)?))?;
+                self.push(self.create_callback(m)?)?;
                 rawset_field(state, -2, &k)?;
             }
             field_getters_index = Some(ffi::lua_absindex(state, -1));
@@ -2702,7 +2699,7 @@ impl Lua {
         if field_setters_nrec > 0 {
             push_table(state, 0, field_setters_nrec, true)?;
             for (k, m) in registry.field_setters {
-                self.push_value(Value::Function(self.create_callback(m)?))?;
+                self.push(self.create_callback(m)?)?;
                 rawset_field(state, -2, &k)?;
             }
             field_setters_index = Some(ffi::lua_absindex(state, -1));
@@ -2725,12 +2722,12 @@ impl Lua {
                 }
             }
             for (k, m) in registry.methods {
-                self.push_value(Value::Function(self.create_callback(m)?))?;
+                self.push(self.create_callback(m)?)?;
                 rawset_field(state, -2, &k)?;
             }
             #[cfg(feature = "async")]
             for (k, m) in registry.async_methods {
-                self.push_value(Value::Function(self.create_async_callback(m)?))?;
+                self.push(self.create_async_callback(m)?)?;
                 rawset_field(state, -2, &k)?;
             }
             match index_type {
@@ -2965,8 +2962,7 @@ impl Lua {
                 match fut.as_mut().poll(&mut ctx) {
                     Poll::Pending => {
                         ffi::lua_pushnil(state);
-                        let pending = &ASYNC_POLL_PENDING as *const u8 as *mut c_void;
-                        ffi::lua_pushlightuserdata(state, pending);
+                        ffi::lua_pushlightuserdata(state, Lua::poll_pending().0);
                         Ok(2)
                     }
                     Poll::Ready(nresults) => {
@@ -2982,7 +2978,7 @@ impl Lua {
                             nresults => {
                                 let results = MultiValue::from_stack_multi(nresults, lua)?;
                                 ffi::lua_pushinteger(state, nresults as _);
-                                lua.push_value(Value::Table(lua.create_sequence_from(results)?))?;
+                                lua.push(lua.create_sequence_from(results)?)?;
                                 Ok(2)
                             }
                         }
@@ -3069,6 +3065,14 @@ impl Lua {
         mem::replace(&mut (*self.extra.get()).waker, waker)
     }
 
+    /// Returns internal `Poll::Pending` constant used for executing async callbacks.
+    #[cfg(feature = "async")]
+    #[doc(hidden)]
+    #[inline]
+    pub fn poll_pending() -> LightUserData {
+        LightUserData(&ASYNC_POLL_PENDING as *const u8 as *mut c_void)
+    }
+
     pub(crate) unsafe fn make_userdata<T>(&self, data: UserDataCell<T>) -> Result<AnyUserData>
     where
         T: UserData + 'static,

src/multi.rs

@@ -23,6 +23,20 @@ impl<'lua, T: IntoLua<'lua>, E: IntoLua<'lua>> IntoLuaMulti<'lua> for StdResult<
         }
         Ok(result)
     }
+
+    #[inline]
+    unsafe fn push_into_stack_multi(self, lua: &'lua Lua) -> Result<c_int> {
+        match self {
+            Ok(v) => v.push_into_stack(lua).map(|_| 1),
+            Err(e) => {
+                let state = lua.state();
+                check_stack(state, 3)?;
+                ffi::lua_pushnil(state);
+                e.push_into_stack(lua)?;
+                Ok(2)
+            }
+        }
+    }
 }
 
 impl<'lua, E: IntoLua<'lua>> IntoLuaMulti<'lua> for StdResult<(), E> {
@@ -38,6 +52,20 @@ impl<'lua, E: IntoLua<'lua>> IntoLuaMulti<'lua> for StdResult<(), E> {
             }
         }
     }
+
+    #[inline]
+    unsafe fn push_into_stack_multi(self, lua: &'lua Lua) -> Result<c_int> {
+        match self {
+            Ok(_) => Ok(0),
+            Err(e) => {
+                let state = lua.state();
+                check_stack(state, 3)?;
+                ffi::lua_pushnil(state);
+                e.push_into_stack(lua)?;
+                Ok(2)
+            }
+        }
+    }
 }
 
 impl<'lua, T: IntoLua<'lua>> IntoLuaMulti<'lua> for T {

src/scope.rs

@@ -19,7 +19,7 @@ use crate::util::{
     self, assert_stack, check_stack, init_userdata_metatable, push_string, push_table,
     rawset_field, short_type_name, take_userdata, StackGuard,
 };
-use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, Value};
+use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti};
 
 #[cfg(feature = "lua54")]
 use crate::userdata::USER_VALUE_MAXSLOT;
@@ -405,7 +405,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             let meta_methods_nrec = registry.meta_methods.len() + registry.meta_fields.len() + 1;
             push_table(state, 0, meta_methods_nrec, true)?;
             for (k, m) in registry.meta_methods {
-                lua.push_value(Value::Function(wrap_method(self, ud_ptr, &k, m)?))?;
+                lua.push(wrap_method(self, ud_ptr, &k, m)?)?;
                 rawset_field(state, -2, MetaMethod::validate(&k)?)?;
             }
             let mut has_name = false;
@@ -455,7 +455,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             if field_getters_nrec > 0 {
                 push_table(state, 0, field_getters_nrec, true)?;
                 for (k, m) in registry.field_getters {
-                    lua.push_value(Value::Function(wrap_method(self, ud_ptr, &k, m)?))?;
+                    lua.push(wrap_method(self, ud_ptr, &k, m)?)?;
                     rawset_field(state, -2, &k)?;
                 }
                 field_getters_index = Some(ffi::lua_absindex(state, -1));
@@ -466,7 +466,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             if field_setters_nrec > 0 {
                 push_table(state, 0, field_setters_nrec, true)?;
                 for (k, m) in registry.field_setters {
-                    lua.push_value(Value::Function(wrap_method(self, ud_ptr, &k, m)?))?;
+                    lua.push(wrap_method(self, ud_ptr, &k, m)?)?;
                     rawset_field(state, -2, &k)?;
                 }
                 field_setters_index = Some(ffi::lua_absindex(state, -1));
@@ -478,7 +478,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
                 // Create table used for methods lookup
                 push_table(state, 0, methods_nrec, true)?;
                 for (k, m) in registry.methods {
-                    lua.push_value(Value::Function(wrap_method(self, ud_ptr, &k, m)?))?;
+                    lua.push(wrap_method(self, ud_ptr, &k, m)?)?;
                     rawset_field(state, -2, &k)?;
                 }
                 methods_index = Some(ffi::lua_absindex(state, -1));

src/string.rs

@@ -132,7 +132,7 @@ impl<'lua> String<'lua> {
         }
     }
 
-    /// Converts the string to a generic C pointer.
+    /// Converts this string to a generic C pointer.
     ///
     /// There is no way to convert the pointer back to its original value.
     ///

src/table.rs

@@ -591,7 +591,7 @@ impl<'lua> Table<'lua> {
         unsafe { ffi::lua_getreadonly(ref_thread, self.0.index) != 0 }
     }
 
-    /// Converts the table to a generic C pointer.
+    /// Converts this table to a generic C pointer.
     ///
     /// Different tables will give different pointers.
     /// There is no way to convert the pointer back to its original value.
@@ -721,7 +721,6 @@ impl<'lua> Table<'lua> {
         TableSequence {
             table: self.0,
             index: 1,
-            len: None,
             _phantom: PhantomData,
         }
     }
@@ -733,17 +732,25 @@ impl<'lua> Table<'lua> {
     }
 
     #[cfg(feature = "serialize")]
-    pub(crate) fn sequence_values_by_len<V: FromLua<'lua>>(
-        self,
-        len: Option<usize>,
-    ) -> TableSequence<'lua, V> {
-        let len = len.unwrap_or_else(|| self.raw_len()) as Integer;
-        TableSequence {
-            table: self.0,
-            index: 1,
-            len: Some(len),
-            _phantom: PhantomData,
+    pub(crate) fn for_each_value<V>(&self, mut f: impl FnMut(V) -> Result<()>) -> Result<()>
+    where
+        V: FromLua<'lua>,
+    {
+        let lua = self.0.lua;
+        let state = lua.state();
+        unsafe {
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
+
+            lua.push_ref(&self.0);
+            let len = ffi::lua_rawlen(state, -1);
+            for i in 1..=len {
+                ffi::lua_rawgeti(state, -1, i as _);
+                f(V::from_stack(-1, lua)?)?;
+                ffi::lua_pop(state, 1);
+            }
         }
+        Ok(())
     }
 
     /// Sets element value at position `idx` without invoking metamethods.
@@ -1085,6 +1092,13 @@ impl<'a, 'lua> Serialize for SerializableTable<'a, 'lua> {
         use crate::serde::de::{check_value_for_skip, MapPairs};
         use crate::value::SerializableValue;
 
+        let convert_result = |res: Result<()>, serialize_err: Option<S::Error>| match res {
+            Ok(v) => Ok(v),
+            Err(Error::SerializeError(_)) if serialize_err.is_some() => Err(serialize_err.unwrap()),
+            Err(Error::SerializeError(msg)) => Err(serde::ser::Error::custom(msg)),
+            Err(err) => Err(serde::ser::Error::custom(err.to_string())),
+        };
+
         let options = self.options;
         let visited = &self.visited;
         visited.borrow_mut().insert(self.table.to_pointer());
@@ -1093,15 +1107,21 @@ impl<'a, 'lua> Serialize for SerializableTable<'a, 'lua> {
         let len = self.table.raw_len();
         if len > 0 || self.table.is_array() {
             let mut seq = serializer.serialize_seq(Some(len))?;
-            for value in self.table.clone().sequence_values_by_len::<Value>(None) {
-                let value = &value.map_err(serde::ser::Error::custom)?;
-                let skip = check_value_for_skip(value, self.options, &self.visited)
-                    .map_err(serde::ser::Error::custom)?;
+            let mut serialize_err = None;
+            let res = self.table.for_each_value::<Value>(|value| {
+                let skip = check_value_for_skip(&value, self.options, &self.visited)
+                    .map_err(|err| Error::SerializeError(err.to_string()))?;
                 if skip {
-                    continue;
+                    // continue iteration
+                    return Ok(());
                 }
-                seq.serialize_element(&SerializableValue::new(value, options, Some(visited)))?;
-            }
+                seq.serialize_element(&SerializableValue::new(&value, options, Some(visited)))
+                    .map_err(|err| {
+                        serialize_err = Some(err);
+                        Error::SerializeError(String::new())
+                    })
+            });
+            convert_result(res, serialize_err)?;
             return seq.end();
         }
 
@@ -1138,18 +1158,7 @@ impl<'a, 'lua> Serialize for SerializableTable<'a, 'lua> {
                     process_pair(key, value)
                 })
         };
-        match res {
-            Ok(_) => {}
-            Err(Error::SerializeError(_)) if serialize_err.is_some() => {
-                return Err(serialize_err.unwrap());
-            }
-            Err(Error::SerializeError(msg)) => {
-                return Err(serde::ser::Error::custom(msg));
-            }
-            Err(err) => {
-                return Err(serde::ser::Error::custom(err.to_string()));
-            }
-        }
+        convert_result(res, serialize_err)?;
         map.end()
     }
 }
@@ -1219,9 +1228,9 @@ where
 ///
 /// [`Table::sequence_values`]: crate::Table::sequence_values
 pub struct TableSequence<'lua, V> {
+    // TODO: Use `&Table`
     table: LuaRef<'lua>,
     index: Integer,
-    len: Option<Integer>,
     _phantom: PhantomData<V>,
 }
 
@@ -1242,7 +1251,7 @@ where
 
             lua.push_ref(&self.table);
             match ffi::lua_rawgeti(state, -1, self.index) {
-                ffi::LUA_TNIL if self.index > self.len.unwrap_or(0) => None,
+                ffi::LUA_TNIL => None,
                 _ => {
                     self.index += 1;
                     Some(V::from_stack(-1, lua))

src/thread.rs

@@ -1,4 +1,4 @@
-use std::os::raw::c_int;
+use std::os::raw::{c_int, c_void};
 
 use crate::error::{Error, Result};
 #[allow(unused)]
@@ -15,7 +15,7 @@ use crate::{
 
 #[cfg(feature = "async")]
 use {
-    crate::{lua::ASYNC_POLL_PENDING, value::MultiValue},
+    crate::value::MultiValue,
     futures_util::stream::Stream,
     std::{
         future::Future,
@@ -375,6 +375,16 @@ impl<'lua> Thread<'lua> {
         }
     }
 
+    /// Converts this thread to a generic C pointer.
+    ///
+    /// There is no way to convert the pointer back to its original value.
+    ///
+    /// Typically this function is used only for hashing and debug information.
+    #[inline]
+    pub fn to_pointer(&self) -> *const c_void {
+        self.0.to_pointer()
+    }
+
     /// Convert this handle to owned version.
     #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
     #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
@@ -530,12 +540,7 @@ where
 #[cfg(feature = "async")]
 #[inline(always)]
 unsafe fn is_poll_pending(state: *mut ffi::lua_State) -> bool {
-    if ffi::lua_islightuserdata(state, -1) != 0 {
-        let stack_ptr = ffi::lua_touserdata(state, -1) as *const u8;
-        let pending_ptr = &ASYNC_POLL_PENDING as *const u8;
-        return std::ptr::eq(stack_ptr, pending_ptr);
-    }
-    false
+    ffi::lua_tolightuserdata(state, -1) == Lua::poll_pending().0
 }
 
 #[cfg(feature = "async")]

src/userdata.rs

@@ -5,7 +5,7 @@ use std::fmt;
 use std::hash::Hash;
 use std::mem;
 use std::ops::{Deref, DerefMut};
-use std::os::raw::{c_char, c_int};
+use std::os::raw::{c_char, c_int, c_void};
 use std::string::String as StdString;
 
 #[cfg(feature = "async")]
@@ -919,7 +919,7 @@ impl<'lua> AnyUserData<'lua> {
             check_stack(state, 5)?;
 
             lua.push_userdata_ref(&self.0)?;
-            lua.push_value(v.into_lua(lua)?)?;
+            lua.push(v)?;
 
             #[cfg(feature = "lua54")]
             if n < USER_VALUE_MAXSLOT {
@@ -1014,7 +1014,7 @@ impl<'lua> AnyUserData<'lua> {
             check_stack(state, 5)?;
 
             lua.push_userdata_ref(&self.0)?;
-            lua.push_value(v.into_lua(lua)?)?;
+            lua.push(v)?;
 
             // Multiple (extra) user values are emulated by storing them in a table
             protect_lua!(state, 2, 0, |state| {
@@ -1096,6 +1096,16 @@ impl<'lua> AnyUserData<'lua> {
         }
     }
 
+    /// Converts this userdata to a generic C pointer.
+    ///
+    /// There is no way to convert the pointer back to its original value.
+    ///
+    /// Typically this function is used only for hashing and debug information.
+    #[inline]
+    pub fn to_pointer(&self) -> *const c_void {
+        self.0.to_pointer()
+    }
+
     /// Convert this handle to owned version.
     #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
     #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]

src/util/mod.rs

@@ -1045,6 +1045,8 @@ pub(crate) unsafe fn to_string(state: *mut ffi::lua_State, index: c_int) -> Stri
         ffi::LUA_TTHREAD => format!("<thread {:?}>", ffi::lua_topointer(state, index)),
         #[cfg(feature = "luau")]
         ffi::LUA_TBUFFER => format!("<buffer {:?}>", ffi::lua_topointer(state, index)),
+        #[cfg(feature = "luajit")]
+        ffi::LUA_TCDATA => format!("<cdata {:?}>", ffi::lua_topointer(state, index)),
         _ => "<unknown>".to_string(),
     }
 }

tests/async.rs

@@ -443,7 +443,7 @@ async fn test_async_userdata() -> Result<()> {
     let globals = lua.globals();
 
     let userdata = lua.create_userdata(MyUserData(11))?;
-    globals.set("userdata", userdata.clone())?;
+    globals.set("userdata", &userdata)?;
 
     lua.load(
         r#"

tests/compile/async_any_userdata_method.stderr

@@ -4,7 +4,7 @@ error: lifetime may not live long enough
 9  |           reg.add_async_method("t", |_, this: &String, ()| async {
    |  ___________________________________----------------------_^
    | |                                   |                    |
-   | |                                   |                    return type of closure `[async block@$DIR/tests/compile/async_any_userdata_method.rs:9:58: 12:10]` contains a lifetime `'2`
+   | |                                   |                    return type of closure `{async block@$DIR/tests/compile/async_any_userdata_method.rs:9:58: 12:10}` contains a lifetime `'2`
    | |                                   lifetime `'1` represents this closure's body
 10 | |             s = this;
 11 | |             Ok(())
@@ -27,6 +27,8 @@ error[E0596]: cannot borrow `s` as mutable, as it is a captured variable in a `F
 error[E0597]: `s` does not live long enough
   --> tests/compile/async_any_userdata_method.rs:8:21
    |
+7  |           let s = String::new();
+   |               - binding `s` declared here
 8  |           let mut s = &s;
    |                       ^^ borrowed value does not live long enough
 9  | /         reg.add_async_method("t", |_, this: &String, ()| async {

tests/compile/lua_norefunwindsafe.stderr

@@ -7,14 +7,46 @@ error[E0277]: the type `UnsafeCell<mlua::lua::ExtraData>` may contain interior m
   |     required by a bound introduced by this call
   |
   = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<mlua::lua::ExtraData>`
-  = note: required because it appears within the type `ArcInner<UnsafeCell<ExtraData>>`
-  = note: required because it appears within the type `PhantomData<ArcInner<UnsafeCell<ExtraData>>>`
-  = note: required because it appears within the type `Arc<UnsafeCell<ExtraData>>`
-  = note: required because it appears within the type `LuaInner`
-  = note: required because it appears within the type `ArcInner<LuaInner>`
-  = note: required because it appears within the type `PhantomData<ArcInner<LuaInner>>`
-  = note: required because it appears within the type `Arc<LuaInner>`
-  = note: required because it appears within the type `Lua`
+note: required because it appears within the type `ArcInner<UnsafeCell<ExtraData>>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | struct ArcInner<T: ?Sized> {
+  |        ^^^^^^^^
+note: required because it appears within the type `PhantomData<ArcInner<UnsafeCell<ExtraData>>>`
+ --> $RUST/core/src/marker.rs
+  |
+  | pub struct PhantomData<T: ?Sized>;
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `Arc<UnsafeCell<ExtraData>>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | pub struct Arc<
+  |            ^^^
+note: required because it appears within the type `LuaInner`
+ --> src/lua.rs
+  |
+  | pub struct LuaInner {
+  |            ^^^^^^^^
+note: required because it appears within the type `ArcInner<LuaInner>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | struct ArcInner<T: ?Sized> {
+  |        ^^^^^^^^
+note: required because it appears within the type `PhantomData<ArcInner<LuaInner>>`
+ --> $RUST/core/src/marker.rs
+  |
+  | pub struct PhantomData<T: ?Sized>;
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `Arc<LuaInner>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | pub struct Arc<
+  |            ^^^
+note: required because it appears within the type `Lua`
+ --> src/lua.rs
+  |
+  | pub struct Lua(Arc<LuaInner>);
+  |            ^^^
   = note: required for `&Lua` to implement `UnwindSafe`
 note: required because it's used within this closure
  --> tests/compile/lua_norefunwindsafe.rs:7:18

tests/compile/non_send.stderr

@@ -4,22 +4,25 @@ error[E0277]: `Rc<Cell<i32>>` cannot be sent between threads safely
 11 |       lua.create_function(move |_, ()| {
    |           --------------- ^-----------
    |           |               |
-   |  _________|_______________within this `[closure@$DIR/tests/compile/non_send.rs:11:25: 11:37]`
+   |  _________|_______________within this `{closure@$DIR/tests/compile/non_send.rs:11:25: 11:37}`
    | |         |
    | |         required by a bound introduced by this call
 12 | |         Ok(data.get())
 13 | |     })?
    | |_____^ `Rc<Cell<i32>>` cannot be sent between threads safely
    |
-   = help: within `[closure@$DIR/tests/compile/non_send.rs:11:25: 11:37]`, the trait `Send` is not implemented for `Rc<Cell<i32>>`
+   = help: within `{closure@$DIR/tests/compile/non_send.rs:11:25: 11:37}`, the trait `Send` is not implemented for `Rc<Cell<i32>>`
 note: required because it's used within this closure
   --> tests/compile/non_send.rs:11:25
    |
 11 |     lua.create_function(move |_, ()| {
    |                         ^^^^^^^^^^^^
-   = note: required for `[closure@$DIR/tests/compile/non_send.rs:11:25: 11:37]` to implement `mlua::types::MaybeSend`
+   = note: required for `{closure@$DIR/tests/compile/non_send.rs:11:25: 11:37}` to implement `mlua::types::MaybeSend`
 note: required by a bound in `Lua::create_function`
   --> src/lua.rs
    |
+   |     pub fn create_function<'lua, A, R, F>(&'lua self, func: F) -> Result<Function<'lua>>
+   |            --------------- required by a bound in this associated function
+...
    |         F: Fn(&'lua Lua, A) -> Result<R> + MaybeSend + 'static,
    |                                            ^^^^^^^^^ required by this bound in `Lua::create_function`

tests/compile/ref_nounwindsafe.stderr

@@ -7,17 +7,57 @@ error[E0277]: the type `UnsafeCell<mlua::lua::ExtraData>` may contain interior m
   |     required by a bound introduced by this call
   |
   = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<mlua::lua::ExtraData>`
-  = note: required because it appears within the type `ArcInner<UnsafeCell<ExtraData>>`
-  = note: required because it appears within the type `PhantomData<ArcInner<UnsafeCell<ExtraData>>>`
-  = note: required because it appears within the type `Arc<UnsafeCell<ExtraData>>`
-  = note: required because it appears within the type `LuaInner`
-  = note: required because it appears within the type `ArcInner<LuaInner>`
-  = note: required because it appears within the type `PhantomData<ArcInner<LuaInner>>`
-  = note: required because it appears within the type `Arc<LuaInner>`
-  = note: required because it appears within the type `Lua`
+note: required because it appears within the type `ArcInner<UnsafeCell<ExtraData>>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | struct ArcInner<T: ?Sized> {
+  |        ^^^^^^^^
+note: required because it appears within the type `PhantomData<ArcInner<UnsafeCell<ExtraData>>>`
+ --> $RUST/core/src/marker.rs
+  |
+  | pub struct PhantomData<T: ?Sized>;
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `Arc<UnsafeCell<ExtraData>>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | pub struct Arc<
+  |            ^^^
+note: required because it appears within the type `LuaInner`
+ --> src/lua.rs
+  |
+  | pub struct LuaInner {
+  |            ^^^^^^^^
+note: required because it appears within the type `ArcInner<LuaInner>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | struct ArcInner<T: ?Sized> {
+  |        ^^^^^^^^
+note: required because it appears within the type `PhantomData<ArcInner<LuaInner>>`
+ --> $RUST/core/src/marker.rs
+  |
+  | pub struct PhantomData<T: ?Sized>;
+  |            ^^^^^^^^^^^
+note: required because it appears within the type `Arc<LuaInner>`
+ --> $RUST/alloc/src/sync.rs
+  |
+  | pub struct Arc<
+  |            ^^^
+note: required because it appears within the type `Lua`
+ --> src/lua.rs
+  |
+  | pub struct Lua(Arc<LuaInner>);
+  |            ^^^
   = note: required for `&Lua` to implement `UnwindSafe`
-  = note: required because it appears within the type `LuaRef<'_>`
-  = note: required because it appears within the type `Table<'_>`
+note: required because it appears within the type `LuaRef<'_>`
+ --> src/types.rs
+  |
+  | pub(crate) struct LuaRef<'lua> {
+  |                   ^^^^^^
+note: required because it appears within the type `Table<'_>`
+ --> src/table.rs
+  |
+  | pub struct Table<'lua>(pub(crate) LuaRef<'lua>);
+  |            ^^^^^
 note: required because it's used within this closure
  --> tests/compile/ref_nounwindsafe.rs:8:18
   |

tests/compile/scope_userdata_borrow.stderr

@@ -4,6 +4,8 @@ error[E0597]: `ibad` does not live long enough
 11 |     lua.scope(|scope| {
    |                ----- has type `&mlua::Scope<'_, '1>`
 ...
+14 |             let ibad = 42;
+   |                 ---- binding `ibad` declared here
 15 |             scope.create_nonstatic_userdata(MyUserData(&ibad)).unwrap();
    |             -------------------------------------------^^^^^--
    |             |                                          |

tests/compile/static_callback_args.stderr

@@ -1,35 +1,31 @@
 error[E0597]: `lua` does not live long enough
   --> tests/compile/static_callback_args.rs:12:5
    |
-10 |        let lua = Lua::new();
-   |            --- binding `lua` declared here
+10 |       let lua = Lua::new();
+   |           --- binding `lua` declared here
 11 |
-12 | /      lua.create_function(|_, table: Table| {
-13 | |/         BAD_TIME.with(|bt| {
-14 | ||             *bt.borrow_mut() = Some(table);
-15 | ||         });
-   | ||__________- argument requires that `lua` is borrowed for `'static`
-16 | |          Ok(())
-17 | |      })?
-   | |_______^ borrowed value does not live long enough
+12 |       lua.create_function(|_, table: Table| {
+   |       ^^^ borrowed value does not live long enough
+13 | /         BAD_TIME.with(|bt| {
+14 | |             *bt.borrow_mut() = Some(table);
+15 | |         });
+   | |__________- argument requires that `lua` is borrowed for `'static`
 ...
-32 |    }
-   |    - `lua` dropped here while still borrowed
+32 |   }
+   |   - `lua` dropped here while still borrowed
 
 error[E0505]: cannot move out of `lua` because it is borrowed
   --> tests/compile/static_callback_args.rs:22:10
    |
-10 |        let lua = Lua::new();
-   |            --- binding `lua` declared here
+10 |       let lua = Lua::new();
+   |           --- binding `lua` declared here
 11 |
-12 | /      lua.create_function(|_, table: Table| {
-13 | |/         BAD_TIME.with(|bt| {
-14 | ||             *bt.borrow_mut() = Some(table);
-15 | ||         });
-   | ||__________- argument requires that `lua` is borrowed for `'static`
-16 | |          Ok(())
-17 | |      })?
-   | |_______- borrow of `lua` occurs here
+12 |       lua.create_function(|_, table: Table| {
+   |       --- borrow of `lua` occurs here
+13 | /         BAD_TIME.with(|bt| {
+14 | |             *bt.borrow_mut() = Some(table);
+15 | |         });
+   | |__________- argument requires that `lua` is borrowed for `'static`
 ...
-22 |        drop(lua);
-   |             ^^^ move out of `lua` occurs here
+22 |       drop(lua);
+   |            ^^^ move out of `lua` occurs here

tests/conversion.rs

@@ -3,7 +3,270 @@ use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::ffi::{CStr, CString};
 
 use maplit::{btreemap, btreeset, hashmap, hashset};
-use mlua::{Error, Lua, Result};
+use mlua::{
+    AnyUserData, Error, Function, IntoLua, Lua, RegistryKey, Result, Table, Thread, UserDataRef,
+    Value,
+};
+
+#[test]
+fn test_value_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let v = Value::Boolean(true);
+    let v2 = (&v).into_lua(&lua)?;
+    assert_eq!(v, v2);
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("v", &v)?;
+    assert_eq!(v, table.get::<_, Value>("v")?);
+
+    Ok(())
+}
+
+#[test]
+fn test_string_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let s = lua.create_string("hello, world!")?;
+    let s2 = (&s).into_lua(&lua)?;
+    assert_eq!(s, s2.as_string().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("s", &s)?;
+    assert_eq!(s, table.get::<_, String>("s")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_string_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let s = lua.create_string("hello, world")?.into_owned();
+    let s2 = (&s).into_lua(&lua)?;
+    assert_eq!(s.to_ref(), *s2.as_string().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("s", &s)?;
+    assert_eq!(s.to_ref(), table.get::<_, String>("s")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_string_from_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    let s = lua.unpack::<mlua::OwnedString>(lua.pack("hello, world")?)?;
+    assert_eq!(s.to_ref(), "hello, world");
+
+    Ok(())
+}
+
+#[test]
+fn test_table_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let t = lua.create_table()?;
+    let t2 = (&t).into_lua(&lua)?;
+    assert_eq!(&t, t2.as_table().unwrap());
+
+    // Push into stack
+    let f = lua.create_function(|_, (t, s): (Table, String)| t.set("s", s))?;
+    f.call((&t, "hello"))?;
+    assert_eq!("hello", t.get::<_, String>("s")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_table_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let t = lua.create_table()?.into_owned();
+    let t2 = (&t).into_lua(&lua)?;
+    assert_eq!(t.to_ref(), *t2.as_table().unwrap());
+
+    // Push into stack
+    let f = lua.create_function(|_, (t, s): (Table, String)| t.set("s", s))?;
+    f.call((&t, "hello"))?;
+    assert_eq!("hello", t.to_ref().get::<_, String>("s")?);
+
+    Ok(())
+}
+
+#[test]
+fn test_function_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let f = lua.create_function(|_, ()| Ok::<_, Error>(()))?;
+    let f2 = (&f).into_lua(&lua)?;
+    assert_eq!(&f, f2.as_function().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("f", &f)?;
+    assert_eq!(f, table.get::<_, Function>("f")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_function_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let f = lua
+        .create_function(|_, ()| Ok::<_, Error>(()))?
+        .into_owned();
+    let f2 = (&f).into_lua(&lua)?;
+    assert_eq!(f.to_ref(), *f2.as_function().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("f", &f)?;
+    assert_eq!(f.to_ref(), table.get::<_, Function>("f")?);
+
+    Ok(())
+}
+
+#[test]
+fn test_thread_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let f = lua.create_function(|_, ()| Ok::<_, Error>(()))?;
+    let th = lua.create_thread(f)?;
+    let th2 = (&th).into_lua(&lua)?;
+    assert_eq!(&th, th2.as_thread().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("th", &th)?;
+    assert_eq!(th, table.get::<_, Thread>("th")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_thread_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let f = lua.create_function(|_, ()| Ok::<_, Error>(()))?;
+    let th = lua.create_thread(f)?.into_owned();
+    let th2 = (&th).into_lua(&lua)?;
+    assert_eq!(&th.to_ref(), th2.as_thread().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("th", &th)?;
+    assert_eq!(th.to_ref(), table.get::<_, Thread>("th")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_thread_from_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    let th = lua.unpack::<mlua::OwnedThread>(Value::Thread(lua.current_thread()))?;
+    assert_eq!(th.to_ref(), lua.current_thread());
+
+    Ok(())
+}
+
+#[test]
+fn test_anyuserdata_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let ud = lua.create_any_userdata(String::from("hello"))?;
+    let ud2 = (&ud).into_lua(&lua)?;
+    assert_eq!(&ud, ud2.as_userdata().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("ud", &ud)?;
+    assert_eq!(ud, table.get::<_, AnyUserData>("ud")?);
+    assert_eq!("hello", *table.get::<_, UserDataRef<String>>("ud")?);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_anyuserdata_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    // Direct conversion
+    let ud = lua.create_any_userdata(String::from("hello"))?.into_owned();
+    let ud2 = (&ud).into_lua(&lua)?;
+    assert_eq!(ud.to_ref(), *ud2.as_userdata().unwrap());
+
+    // Push into stack
+    let table = lua.create_table()?;
+    table.set("ud", &ud)?;
+    assert_eq!(ud.to_ref(), table.get::<_, AnyUserData>("ud")?);
+    assert_eq!("hello", *table.get::<_, UserDataRef<String>>("ud")?);
+
+    Ok(())
+}
+
+#[test]
+fn test_registry_value_into_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    let t = lua.create_table()?;
+    let r = lua.create_registry_value(t)?;
+    let f = lua.create_function(|_, t: Table| t.raw_set("hello", "world"))?;
+
+    f.call(&r)?;
+    let v = r.into_lua(&lua)?;
+    let t = v.as_table().unwrap();
+    assert_eq!(t.get::<_, String>("hello")?, "world");
+
+    // Try to set nil registry key
+    let r_nil = lua.create_registry_value(Value::Nil)?;
+    t.set("hello", &r_nil)?;
+    assert_eq!(t.get::<_, Value>("hello")?, Value::Nil);
+
+    // Check non-owned registry key
+    let lua2 = Lua::new();
+    let r2 = lua2.create_registry_value("abc")?;
+    assert!(matches!(
+        f.call::<_, ()>(&r2),
+        Err(Error::MismatchedRegistryKey)
+    ));
+
+    Ok(())
+}
+
+#[test]
+fn test_registry_key_from_lua() -> Result<()> {
+    let lua = Lua::new();
+
+    let fkey = lua.load("function() return 1 end").eval::<RegistryKey>()?;
+    let f = lua.registry_value::<Function>(&fkey)?;
+    assert_eq!(f.call::<_, i32>(())?, 1);
+
+    Ok(())
+}
 
 #[test]
 fn test_conv_vec() -> Result<()> {

tests/function.rs

@@ -231,6 +231,19 @@ fn test_function_info() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_function_pointer() -> Result<()> {
+    let lua = Lua::new();
+
+    let func1 = lua.load("return function() end").into_function()?;
+    let func2 = func1.call::<_, Function>(())?;
+
+    assert_eq!(func1.to_pointer(), func1.clone().to_pointer());
+    assert_ne!(func1.to_pointer(), func2.to_pointer());
+
+    Ok(())
+}
+
 #[test]
 fn test_function_wrap() -> Result<()> {
     use mlua::Error;

tests/luau.rs

@@ -275,6 +275,22 @@ fn test_sandbox() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_sandbox_nolibs() -> Result<()> {
+    let lua = Lua::new_with(StdLib::NONE, LuaOptions::default()).unwrap();
+
+    lua.sandbox(true)?;
+    lua.load("global = 123").exec()?;
+    let n: i32 = lua.load("return global").eval()?;
+    assert_eq!(n, 123);
+    assert_eq!(lua.globals().get::<_, Option<i32>>("global")?, Some(123));
+
+    lua.sandbox(false)?;
+    assert_eq!(lua.globals().get::<_, Option<i32>>("global")?, None);
+
+    Ok(())
+}
+
 #[test]
 fn test_sandbox_threads() -> Result<()> {
     let lua = Lua::new();

tests/multi.rs

@@ -0,0 +1,60 @@
+use mlua::{Error, ExternalError, IntoLuaMulti, Lua, Result, String, Value};
+
+#[test]
+fn test_result_conversions() -> Result<()> {
+    let lua = Lua::new();
+    let globals = lua.globals();
+
+    let ok = lua.create_function(|_, ()| Ok(Ok::<(), Error>(())))?;
+    let err = lua.create_function(|_, ()| Ok(Err::<(), _>("failure1".into_lua_err())))?;
+    let ok2 = lua.create_function(|_, ()| Ok(Ok::<_, Error>("!".to_owned())))?;
+    let err2 = lua.create_function(|_, ()| Ok(Err::<String, _>("failure2".into_lua_err())))?;
+
+    globals.set("ok", ok)?;
+    globals.set("ok2", ok2)?;
+    globals.set("err", err)?;
+    globals.set("err2", err2)?;
+
+    lua.load(
+        r#"
+        local r, e = ok()
+        assert(r == nil and e == nil)
+
+        local r, e = err()
+        assert(r == nil)
+        assert(tostring(e):find("failure1") ~= nil)
+
+        local r, e = ok2()
+        assert(r == "!")
+        assert(e == nil)
+
+        local r, e = err2()
+        assert(r == nil)
+        assert(tostring(e):find("failure2") ~= nil)
+    "#,
+    )
+    .exec()?;
+
+    // Try to convert Result into MultiValue
+    let ok1 = Ok::<(), Error>(());
+    let multi_ok1 = ok1.into_lua_multi(&lua)?;
+    assert_eq!(multi_ok1.len(), 0);
+    let err1 = Err::<(), _>("failure1");
+    let multi_err1 = err1.into_lua_multi(&lua)?;
+    assert_eq!(multi_err1.len(), 2);
+    assert_eq!(multi_err1[0], Value::Nil);
+    assert_eq!(multi_err1[1].as_str().unwrap(), "failure1");
+
+    let ok2 = Ok::<_, Error>("!");
+    let multi_ok2 = ok2.into_lua_multi(&lua)?;
+    assert_eq!(multi_ok2.len(), 1);
+    assert_eq!(multi_ok2[0].as_str().unwrap(), "!");
+    let err2 = Err::<String, _>("failure2".into_lua_err());
+    let multi_err2 = err2.into_lua_multi(&lua)?;
+    assert_eq!(multi_err2.len(), 2);
+    assert_eq!(multi_err2[0], Value::Nil);
+    assert!(matches!(multi_err2[1], Value::Error(_)));
+    assert_eq!(multi_err2[1].to_string()?, "failure2");
+
+    Ok(())
+}

tests/serde.rs

@@ -598,7 +598,7 @@ fn test_from_value_with_options() -> Result<(), Box<dyn StdError>> {
 
     // Check recursion when using `Serialize` impl
     let t = lua.create_table()?;
-    t.set("t", t.clone())?;
+    t.set("t", &t)?;
     assert!(serde_json::to_string(&t).is_err());
 
     // Serialize Lua globals table

tests/string.rs

@@ -99,6 +99,19 @@ fn test_string_debug() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_string_pointer() -> Result<()> {
+    let lua = Lua::new();
+
+    let str1 = lua.create_string("hello")?;
+    let str2 = lua.create_string("hello")?;
+
+    // Lua uses string interning, so these should be the same
+    assert_eq!(str1.to_pointer(), str2.to_pointer());
+
+    Ok(())
+}
+
 #[cfg(all(feature = "unstable", not(feature = "send")))]
 #[test]
 fn test_owned_string() -> Result<()> {

tests/table.rs

@@ -369,6 +369,19 @@ fn test_table_eq() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_table_pointer() -> Result<()> {
+    let lua = Lua::new();
+
+    let table1 = lua.create_table()?;
+    let table2 = lua.create_table()?;
+
+    assert_eq!(table1.to_pointer(), table1.clone().to_pointer());
+    assert_ne!(table1.to_pointer(), table2.to_pointer());
+
+    Ok(())
+}
+
 #[test]
 fn test_table_error() -> Result<()> {
     let lua = Lua::new();

tests/tests.rs

@@ -504,44 +504,6 @@ fn test_panic() -> Result<()> {
     Ok(())
 }
 
-#[test]
-fn test_result_conversions() -> Result<()> {
-    let lua = Lua::new();
-    let globals = lua.globals();
-
-    let ok = lua.create_function(|_, ()| Ok(Ok::<(), Error>(())))?;
-    let err = lua.create_function(|_, ()| Ok(Err::<(), _>("failure1".into_lua_err())))?;
-    let ok2 = lua.create_function(|_, ()| Ok(Ok::<_, Error>("!".to_owned())))?;
-    let err2 = lua.create_function(|_, ()| Ok(Err::<String, _>("failure2".into_lua_err())))?;
-
-    globals.set("ok", ok)?;
-    globals.set("ok2", ok2)?;
-    globals.set("err", err)?;
-    globals.set("err2", err2)?;
-
-    lua.load(
-        r#"
-        local r, e = ok()
-        assert(r == nil and e == nil)
-
-        local r, e = err()
-        assert(r == nil)
-        assert(tostring(e):find("failure1") ~= nil)
-
-        local r, e = ok2()
-        assert(r == "!")
-        assert(e == nil)
-
-        local r, e = err2()
-        assert(r == nil)
-        assert(tostring(e):find("failure2") ~= nil)
-    "#,
-    )
-    .exec()?;
-
-    Ok(())
-}
-
 #[test]
 fn test_num_conversion() -> Result<()> {
     let lua = Lua::new();
@@ -965,7 +927,7 @@ fn test_recursion() -> Result<()> {
         Ok(())
     })?;
 
-    lua.globals().set("f", f.clone())?;
+    lua.globals().set("f", &f)?;
     f.call::<_, ()>(1)?;
 
     Ok(())
@@ -1003,7 +965,7 @@ fn test_too_many_recursions() -> Result<()> {
     let f = lua
         .create_function(move |lua, ()| lua.globals().get::<_, Function>("f")?.call::<_, ()>(()))?;
 
-    lua.globals().set("f", f.clone())?;
+    lua.globals().set("f", &f)?;
     assert!(f.call::<_, ()>(()).is_err());
 
     Ok(())

tests/thread.rs

@@ -182,7 +182,7 @@ fn test_coroutine_panic() {
         let thrd_main = lua.create_function(|_, ()| -> Result<()> {
             panic!("test_panic");
         })?;
-        lua.globals().set("main", thrd_main.clone())?;
+        lua.globals().set("main", &thrd_main)?;
         let thrd: Thread = lua.create_thread(thrd_main)?;
         thrd.resume(())
     }) {
@@ -191,6 +191,19 @@ fn test_coroutine_panic() {
     }
 }
 
+#[test]
+fn test_thread_pointer() -> Result<()> {
+    let lua = Lua::new();
+
+    let func = lua.load("return 123").into_function()?;
+    let thread = lua.create_thread(func.clone())?;
+
+    assert_eq!(thread.to_pointer(), thread.clone().to_pointer());
+    assert_ne!(thread.to_pointer(), lua.current_thread().to_pointer());
+
+    Ok(())
+}
+
 #[cfg(all(feature = "unstable", not(feature = "send")))]
 #[test]
 fn test_owned_thread() -> Result<()> {

tests/userdata.rs

@@ -58,7 +58,7 @@ fn test_methods() -> Result<()> {
 
     fn check_methods(lua: &Lua, userdata: AnyUserData) -> Result<()> {
         let globals = lua.globals();
-        globals.set("userdata", userdata.clone())?;
+        globals.set("userdata", &userdata)?;
         lua.load(
             r#"
             function get_it()
@@ -342,7 +342,7 @@ fn test_userdata_take() -> Result<()> {
     }
 
     fn check_userdata_take(lua: &Lua, userdata: AnyUserData, rc: Arc<i64>) -> Result<()> {
-        lua.globals().set("userdata", userdata.clone())?;
+        lua.globals().set("userdata", &userdata)?;
         assert_eq!(Arc::strong_count(&rc), 3);
         {
             let _value = userdata.borrow::<MyUserdata>()?;
@@ -474,7 +474,7 @@ fn test_functions() -> Result<()> {
     let lua = Lua::new();
     let globals = lua.globals();
     let userdata = lua.create_userdata(MyUserData(42))?;
-    globals.set("userdata", userdata.clone())?;
+    globals.set("userdata", &userdata)?;
     lua.load(
         r#"
         function get_it()
@@ -951,6 +951,20 @@ fn test_userdata_method_errors() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_userdata_pointer() -> Result<()> {
+    let lua = Lua::new();
+
+    let ud1 = lua.create_any_userdata("hello")?;
+    let ud2 = lua.create_any_userdata("hello")?;
+
+    assert_eq!(ud1.to_pointer(), ud1.clone().to_pointer());
+    // Different userdata objects with the same value should have different pointers
+    assert_ne!(ud1.to_pointer(), ud2.to_pointer());
+
+    Ok(())
+}
+
 #[cfg(all(feature = "unstable", not(feature = "send")))]
 #[test]
 fn test_owned_userdata() -> Result<()> {
@@ -991,9 +1005,9 @@ fn test_userdata_derive() -> Result<()> {
     // More complex struct where generics and where clause
 
     #[derive(Clone, Copy, mlua::FromLua)]
-    struct MyUserData2<'a, T>(&'a T)
+    struct MyUserData2<'a, T: ?Sized>(&'a T)
     where
-        T: ?Sized;
+        T: Copy;
 
     lua.register_userdata_type::<MyUserData2<'static, i32>>(|reg| {
         reg.add_function("val", |_, this: MyUserData2<'static, i32>| Ok(*this.0));