ngcpp · mingxwa · Mar 13, 2026 · Mar 9, 2026 · Mar 12, 2026 · Mar 13, 2026
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.28)
 
-project(msft_proxy4 VERSION 4.0.1 LANGUAGES CXX)
+project(msft_proxy4 VERSION 4.0.2 LANGUAGES CXX)
 add_library(msft_proxy4 INTERFACE)
 set_target_properties(msft_proxy4 PROPERTIES EXPORT_NAME proxy)
 add_library(msft_proxy4::proxy ALIAS msft_proxy4)

diff --git a/LICENSE b/LICENSE
@@ -1,6 +1,7 @@
     MIT License
 
     Copyright (c) 2022-2026 Microsoft Corporation.
+    Copyright (c) 2026-Present Next Gen C++ Foundation.
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal

diff --git a/README.md b/README.md
@@ -16,7 +16,7 @@ If so, this library is for you.
 
 "Proxy" is a modern C++ library that helps you use polymorphism (a way to use different types of objects interchangeably) without needing inheritance.
 
-"Proxy" was created by Microsoft engineers and incubated at Microsoft from 2018 to Feb 2026, and has been used in the Windows operating system since 2022. It is now maintained by the Next Gen C++ Foundation (ngcpp). This repository was ported from https://github.com/microsoft/proxy, where more historical releases can be found. For many years, using inheritance was the main way to achieve polymorphism in C++. However, new programming languages like [Rust](https://doc.rust-lang.org/book/ch10-02-traits.html) offer better ways to do this. We have improved our understanding of object-oriented programming and decided to use *pointers* in C++ as the foundation for "Proxy". Specifically, the "Proxy" library is designed to be:
+"Proxy" was created by Microsoft engineers and incubated at Microsoft from 2018 to Feb 2026, and has been used in the Windows operating system since 2022. It is now maintained by the Next Gen C++ Foundation (ngcpp). This repository was ported from [microsoft/proxy](https://github.com/microsoft/proxy), where more historical releases can be found. For many years, using inheritance was the main way to achieve polymorphism in C++. However, new programming languages like [Rust](https://doc.rust-lang.org/book/ch10-02-traits.html) offer better ways to do this. We have improved our understanding of object-oriented programming and decided to use *pointers* in C++ as the foundation for "Proxy". Specifically, the "Proxy" library is designed to be:
 
 - **Portable**: "Proxy" was implemented as a header-only library in standard C++20. It can be used on any platform while the compiler supports C++20. The majority of the library is [freestanding](https://en.cppreference.com/w/cpp/freestanding), making it feasible for embedded engineering or kernel design of an operating system.
 - **Non-intrusive**: An implementation type is no longer required to inherit from an abstract binding.

diff --git a/benchmarks/proxy_creation_benchmark.cpp b/benchmarks/proxy_creation_benchmark.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <any>

diff --git a/benchmarks/proxy_operation_benchmark.cpp b/benchmarks/proxy_operation_benchmark.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <benchmark/benchmark.h>

diff --git a/benchmarks/proxy_operation_benchmark_context.cpp b/benchmarks/proxy_operation_benchmark_context.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include "proxy_operation_benchmark_context.h"

diff --git a/benchmarks/proxy_operation_benchmark_context.h b/benchmarks/proxy_operation_benchmark_context.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <any>

diff --git a/docs/resources/icon.png b/docs/resources/icon.png
diff --git a/docs/spec/msft_lib_proxy.md b/docs/spec/msft_lib_proxy.md
@@ -10,6 +10,7 @@ Starting with 3.0.0, Proxy ships a feature-test macro that encodes the library v
 
 | Version | Value of `__msft_lib_proxy` |
 | ------- | --------------------------- |
+| 4.0.2   | `202603L`                   |
 | 4.0.1   | `202510L`                   |
 | 4.0.0   | `202508L`                   |
 | 3.4.0   | `202505L`                   |

diff --git a/include/proxy/proxy.h b/include/proxy/proxy.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef MSFT_PROXY_PROXY_H_

diff --git a/include/proxy/proxy_fmt.h b/include/proxy/proxy_fmt.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef MSFT_PROXY_PROXY_FMT_H_

diff --git a/include/proxy/proxy_macros.h b/include/proxy/proxy_macros.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef MSFT_PROXY_PROXY_MACROS_H_

diff --git a/include/proxy/v4/proxy.h b/include/proxy/v4/proxy.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef MSFT_PROXY_V4_PROXY_H_
@@ -1288,10 +1289,26 @@ struct converter {
   template <class T>
   operator T() && noexcept(
       std::is_nothrow_invocable_r_v<T, F, std::in_place_type_t<T>>)
-    requires(std::is_invocable_r_v<T, F, std::in_place_type_t<T>>)
+    requires(std::is_invocable_r_v<T, F, std::in_place_type_t<T>> &&
+             !std::is_invocable_r_v<T, F, std::in_place_type_t<T&>> &&
+             !std::is_invocable_r_v<T, F, std::in_place_type_t<T &&>>)
   {
     return std::move(f_)(std::in_place_type<T>);
   }
+  template <class T>
+  operator T&() && noexcept(
+      std::is_nothrow_invocable_r_v<T&, F, std::in_place_type_t<T&>>)
+    requires(std::is_invocable_r_v<T&, F, std::in_place_type_t<T&>>)
+  {
+    return std::move(f_)(std::in_place_type<T&>);
+  }
+  template <class T>
+  operator T&&() && noexcept(
+      std::is_nothrow_invocable_r_v<T&&, F, std::in_place_type_t<T&&>>)
+    requires(std::is_invocable_r_v<T &&, F, std::in_place_type_t<T &&>>)
+  {
+    return std::move(f_)(std::in_place_type<T&&>);
+  }
 
 private:
   F f_;
@@ -2346,14 +2363,29 @@ struct sign {
 template <std::size_t N>
 sign(const char (&str)[N]) -> sign<N - 1u>;
 
-struct wildcard {
-  wildcard() = delete;
+// When std::reference_constructs_from_temporary_v (C++23) is not available, we
+// fall back to a conservative approximation that disallows binding a temporary
+// to a reference type if the source type is not a reference or if the source
+// and target reference types are not compatible.
+template <class T, class U>
+concept explicitly_convertible =
+    std::is_constructible_v<U, T> &&
+#if __cpp_lib_reference_from_temporary >= 202202L
+    !std::reference_constructs_from_temporary_v<U, T>;
+#else
+    (!std::is_reference_v<U> ||
+     (std::is_reference_v<T> &&
+      std::is_convertible_v<std::add_pointer_t<std::remove_reference_t<T>>,
+                            std::add_pointer_t<std::remove_reference_t<U>>>));
+#endif // __cpp_lib_reference_from_temporary >= 202202L
 
+struct noreturn_conversion {
   template <class T>
-  [[noreturn]] operator T() const {
+  [[noreturn]] PRO4D_STATIC_CALL(T, std::in_place_type_t<T>) {
     PROD_UNREACHABLE();
   }
 };
+using wildcard = converter<noreturn_conversion>;
 
 } // namespace details
 
@@ -2577,9 +2609,9 @@ struct explicit_conversion_dispatch : details::cast_dispatch_base<true, false> {
   PRO4D_STATIC_CALL(auto, T&& self) noexcept {
     return details::converter{
         [&self]<class U>(std::in_place_type_t<U>) noexcept(
-            std::is_nothrow_constructible_v<U, T>)
-          requires(std::is_constructible_v<U, T>)
-        { return U{std::forward<T>(self)}; }};
+            std::is_nothrow_constructible_v<U, T>) -> U
+          requires(details::explicitly_convertible < T &&, U >)
+        { return static_cast<U>(std::forward<T>(self)); }};
   }
 };
 using conversion_dispatch = explicit_conversion_dispatch;

diff --git a/include/proxy/v4/proxy_fmt.h b/include/proxy/v4/proxy_fmt.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef MSFT_PROXY_V4_PROXY_FMT_H_

diff --git a/include/proxy/v4/proxy_macros.h b/include/proxy/v4/proxy_macros.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef MSFT_PROXY_V4_PROXY_MACROS_H_
@@ -28,7 +29,7 @@
 #define PRO4D_DEBUG(...) __VA_ARGS__
 #endif // NDEBUG
 
-#define __msft_lib_proxy4 202510L
+#define __msft_lib_proxy4 202603L
 
 #define PRO4D_DIRECT_FUNC_IMPL(...)                                            \
   noexcept(noexcept(__VA_ARGS__))                                              \

diff --git a/meson.build b/meson.build
@@ -1,7 +1,7 @@
 project(
   'msft_proxy4',
   'cpp',
-  version: '4.0.1',
+  version: '4.0.2',
   license: 'MIT',
   license_files: 'LICENSE',
   meson_version: '>=1.3',

diff --git a/mkdocs.yml b/mkdocs.yml
@@ -2,7 +2,7 @@
 site_name: Proxy 4
 site_url: https://ngcpp.github.io/proxy
 site_description: Next Generation Polymorphism in C++
-copyright: Copyright (c) 2022-2026 Microsoft Corporation
+copyright: Copyright (c) 2022-2026 Microsoft Corporation<br />Copyright (c) 2026-Present Next Gen C++ Foundation
 repo_url: https://github.com/ngcpp/proxy/
 edit_uri: ""
 

diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
@@ -12,6 +12,7 @@ include(GoogleTest)
 
 add_executable(msft_proxy_tests
   proxy_creation_tests.cpp
+  proxy_details_tests.cpp
   proxy_dispatch_tests.cpp
   proxy_fmt_format_tests.cpp
   proxy_format_tests.cpp

diff --git a/tests/proxy_creation_tests.cpp b/tests/proxy_creation_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include "utils.h"

diff --git a/tests/proxy_details_tests.cpp b/tests/proxy_details_tests.cpp
@@ -0,0 +1,31 @@
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
+// Licensed under the MIT License.
+
+#include <proxy/proxy.h>
+
+namespace proxy_details_tests_details {
+
+struct Base {
+  int v;
+};
+struct Derived : Base {};
+
+static_assert(pro::details::explicitly_convertible<int, int>);
+static_assert(pro::details::explicitly_convertible<long, int>);
+static_assert(!pro::details::explicitly_convertible<int, int&&>);
+static_assert(!pro::details::explicitly_convertible<int, const int&>);
+static_assert(pro::details::explicitly_convertible<int&&, int&&>);
+static_assert(pro::details::explicitly_convertible<int&&, const int&>);
+static_assert(!pro::details::explicitly_convertible<long&&, int&&>);
+static_assert(!pro::details::explicitly_convertible<long, int&&>);
+static_assert(pro::details::explicitly_convertible<Derived&, Base&>);
+static_assert(pro::details::explicitly_convertible<Derived&, const Base&>);
+static_assert(!pro::details::explicitly_convertible<Derived&, Base&&>);
+static_assert(!pro::details::explicitly_convertible<const Derived&, Base&>);
+static_assert(
+    pro::details::explicitly_convertible<const Derived&, const Base&>);
+static_assert(pro::details::explicitly_convertible<Derived, Base>);
+static_assert(!pro::details::explicitly_convertible<Derived, Base&&>);
+static_assert(!pro::details::explicitly_convertible<Base&, Derived&>);
+
+} // namespace proxy_details_tests_details
diff --git a/tests/proxy_dispatch_tests.cpp b/tests/proxy_dispatch_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <gtest/gtest.h>
@@ -783,11 +784,13 @@ TEST(ProxyDispatchTests, TestRhsOpPtrToMem) {
 
 TEST(ProxyDispatchTests, TestIndirectConversion) {
   struct TestFacade
-      : pro::facade_builder::add_convention<pro::conversion_dispatch,
-                                            int()>::build {};
+      : pro::facade_builder                                         //
+        ::add_convention<pro::conversion_dispatch, int(), short&()> //
+        ::build {};
   short v = 123;
   pro::proxy<TestFacade> p = &v;
-  ASSERT_EQ(static_cast<int>(*p), 123);
+  static_cast<short&>(*p) = 456;
+  ASSERT_EQ(static_cast<int>(*p), 456);
 }
 
 TEST(ProxyDispatchTests, TestDirectConversion) {

diff --git a/tests/proxy_fmt_format_tests.cpp b/tests/proxy_fmt_format_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <gtest/gtest.h>

diff --git a/tests/proxy_format_tests.cpp b/tests/proxy_format_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <gtest/gtest.h>

diff --git a/tests/proxy_integration_tests.cpp b/tests/proxy_integration_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <gtest/gtest.h>

diff --git a/tests/proxy_invocation_tests.cpp b/tests/proxy_invocation_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <algorithm>

diff --git a/tests/proxy_lifetime_tests.cpp b/tests/proxy_lifetime_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include "utils.h"

diff --git a/tests/proxy_reflection_tests.cpp b/tests/proxy_reflection_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include "utils.h"

diff --git a/tests/proxy_regression_tests.cpp b/tests/proxy_regression_tests.cpp
@@ -1,8 +1,17 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <gtest/gtest.h>
+#if defined(_MSC_VER) && !defined(__clang__)
+#pragma warning(push)
+#pragma warning(                                                               \
+    disable : 4702) // False alarm from MSVC: warning C4702: unreachable code
+#endif              // defined(_MSC_VER) && !defined(__clang__)
 #include <proxy/proxy.h>
+#if defined(_MSC_VER) && !defined(__clang__)
+#pragma warning(pop)
+#endif // defined(_MSC_VER) && !defined(__clang__)
 #include <vector>
 
 namespace proxy_regression_tests_details {
@@ -39,6 +48,8 @@ struct Range : pro::facade_builder                                          //
                ::template add_convention<MemEnd, pro::proxy<Iterator<T>>()> //
                ::build {};
 
+PRO_DEF_MEM_DISPATCH(MemFun, Fun);
+
 } // namespace proxy_regression_tests_details
 
 namespace details = proxy_regression_tests_details;
@@ -69,3 +80,16 @@ TEST(ProxyRegressionTests, TestProxiableSelfDependency) {
   }
   EXPECT_EQ(expected, original);
 }
+
+// https://github.com/ngcpp/proxy/issues/10
+TEST(ProxyRegressionTests, TestWeakDispatchReferenceReturningOverload) {
+  struct MyFacade
+      : pro::facade_builder                                           //
+        ::add_convention<pro::weak_dispatch<details::MemFun>, int&()> //
+        ::build {};
+  static_assert(pro::proxiable<int*, MyFacade>);
+
+  int v = 123;
+  pro::proxy<MyFacade> p = &v;
+  EXPECT_THROW(p->Fun(), pro::not_implemented);
+}
diff --git a/tests/proxy_rtti_tests.cpp b/tests/proxy_rtti_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <gtest/gtest.h>

diff --git a/tests/proxy_traits_tests.cpp b/tests/proxy_traits_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include "utils.h"

diff --git a/tests/proxy_view_tests.cpp b/tests/proxy_view_tests.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include "utils.h"

diff --git a/tests/utils.h b/tests/utils.h
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #ifndef _MSFT_PROXY_TEST_UTILS_

diff --git a/tools/report_generator/main.cpp b/tools/report_generator/main.cpp
@@ -1,4 +1,5 @@
 // Copyright (c) 2022-2026 Microsoft Corporation.
+// Copyright (c) 2026-Present Next Gen C++ Foundation.
 // Licensed under the MIT License.
 
 #include <cstdio>