[libc++] P0792R14: std::function_ref

libcxx/include/CMakeLists.txt

@@ -393,6 +393,9 @@ set(files
   __functional/compose.h
   __functional/default_searcher.h
   __functional/function.h
+  __functional/function_ref.h
+  __functional/function_ref_common.h
+  __functional/function_ref_impl.h
   __functional/hash.h
   __functional/identity.h
   __functional/invoke.h
@@ -855,6 +858,7 @@ set(files
   __utility/is_valid_range.h
   __utility/move.h
   __utility/no_destroy.h
+  __utility/nontype.h
   __utility/pair.h
   __utility/piecewise_construct.h
   __utility/priority_tag.h

libcxx/include/__functional/function_ref.h

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FUNCTIONAL_FUNCTION_REF_H
+#define _LIBCPP___FUNCTIONAL_FUNCTION_REF_H
+
+#include <__config>
+#include <__functional/function_ref_common.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+// NOLINTBEGIN(readability-duplicate-include)
+
+#define _LIBCPP_FUNCTION_REF_CV
+#define _LIBCPP_FUNCTION_REF_NOEXCEPT false
+#include <__functional/function_ref_impl.h>
+#undef _LIBCPP_FUNCTION_REF_CV
+#undef _LIBCPP_FUNCTION_REF_NOEXCEPT
+
+#define _LIBCPP_FUNCTION_REF_CV
+#define _LIBCPP_FUNCTION_REF_NOEXCEPT true
+#include <__functional/function_ref_impl.h>
+#undef _LIBCPP_FUNCTION_REF_CV
+#undef _LIBCPP_FUNCTION_REF_NOEXCEPT
+
+#define _LIBCPP_FUNCTION_REF_CV const
+#define _LIBCPP_FUNCTION_REF_NOEXCEPT false
+#include <__functional/function_ref_impl.h>
+#undef _LIBCPP_FUNCTION_REF_CV
+#undef _LIBCPP_FUNCTION_REF_NOEXCEPT
+
+#define _LIBCPP_FUNCTION_REF_CV const
+#define _LIBCPP_FUNCTION_REF_NOEXCEPT true
+#include <__functional/function_ref_impl.h>
+#undef _LIBCPP_FUNCTION_REF_CV
+#undef _LIBCPP_FUNCTION_REF_NOEXCEPT
+
+// NOLINTEND(readability-duplicate-include)
+
+#endif // _LIBCPP___FUNCTIONAL_FUNCTION_REF_H

libcxx/include/__functional/function_ref_common.h

@@ -0,0 +1,73 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___FUNCTIONAL_FUNCTION_REF_COMMON_H
+#define _LIBCPP___FUNCTIONAL_FUNCTION_REF_COMMON_H
+
+#include <__config>
+#include <__type_traits/invoke.h>
+#include <__type_traits/is_function.h>
+#include <__type_traits/is_object.h>
+#include <__type_traits/remove_pointer.h>
+#include <__utility/nontype.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+template <class...>
+class function_ref;
+
+template <class>
+inline constexpr bool __is_function_ref = false;
+
+template <class _Rp, class... _ArgTypes>
+inline constexpr bool __is_function_ref<function_ref<_Rp, _ArgTypes...>> = true;
+
+template <class _Fp, class _Tp>
+struct __function_ref_bind {};
+
+template <class _Tp, class _Rp, class _Gp, class... _ArgTypes>
+struct __function_ref_bind<_Rp (*)(_Gp, _ArgTypes...), _Tp> {
+  using type = _Rp(_ArgTypes...);
+};
+
+template <class _Tp, class _Rp, class _Gp, class... _ArgTypes>
+struct __function_ref_bind<_Rp (*)(_Gp, _ArgTypes...) noexcept, _Tp> {
+  using type = _Rp(_ArgTypes...) noexcept;
+};
+
+template <class _Tp, class _Mp, class _Gp>
+  requires is_object_v<_Mp>
+struct __function_ref_bind<_Mp _Gp::*, _Tp> {
+  using type = invoke_result_t<_Mp _Gp::*, _Tp&>();
+};
+
+template <class _Fp, class _Tp>
+using __function_ref_bind_t = __function_ref_bind<_Fp, _Tp>::type;
+
+template <class _Fp>
+  requires is_function_v<_Fp>
+function_ref(_Fp*) -> function_ref<_Fp>;
+
+template <auto _Fn>
+  requires is_function_v<remove_pointer_t<decltype(_Fn)>>
+function_ref(nontype_t<_Fn>) -> function_ref<remove_pointer_t<decltype(_Fn)>>;
+
+template <auto _Fn, class _Tp>
+function_ref(nontype_t<_Fn>, _Tp&&) -> function_ref<__function_ref_bind_t<decltype(_Fn), _Tp&>>;
+
+#endif // _LIBCPP_STD_VER >= 26
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FUNCTIONAL_FUNCTION_REF_COMMON_H

libcxx/include/__functional/function_ref_impl.h

@@ -0,0 +1,179 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <__assert>
+#include <__config>
+#include <__functional/invoke.h>
+#include <__memory/addressof.h>
+#include <__type_traits/invoke.h>
+#include <__type_traits/is_const.h>
+#include <__type_traits/is_function.h>
+#include <__type_traits/is_member_pointer.h>
+#include <__type_traits/is_object.h>
+#include <__type_traits/is_pointer.h>
+#include <__type_traits/is_reference.h>
+#include <__type_traits/is_void.h>
+#include <__type_traits/remove_cvref.h>
+#include <__type_traits/remove_pointer.h>
+#include <__type_traits/remove_reference.h>
+#include <__utility/forward.h>
+#include <__utility/nontype.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+template <class...>
+class function_ref;
+
+template <class _Rp, class... _ArgTypes>
+class function_ref<_Rp(_ArgTypes...) _LIBCPP_FUNCTION_REF_CV noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT)> {
+private:
+#  if _LIBCPP_FUNCTION_REF_NOEXCEPT == true
+  template <class... _Tp>
+  static constexpr bool __is_invocable_using = is_nothrow_invocable_r_v<_Rp, _Tp..., _ArgTypes...>;
+#  else
+  template <class... _Tp>
+  static constexpr bool __is_invocable_using = is_invocable_r_v<_Rp, _Tp..., _ArgTypes...>;
+#  endif
+
+  // use a union instead of a plain `void*` to avoid dropping const qualifiers and casting function pointers to data
+  // pointers
+  union __storage_t {
+    void* __obj_ptr;
+    void const* __obj_const_ptr;
+    void (*__fn_ptr)();
+
+    _LIBCPP_HIDE_FROM_ABI constexpr explicit __storage_t() noexcept : __obj_ptr(nullptr) {}
+
+    template <class _Tp>
+    _LIBCPP_HIDE_FROM_ABI constexpr explicit __storage_t(_Tp* __ptr) noexcept {
+      if constexpr (is_object_v<_Tp>) {
+        if constexpr (is_const_v<_Tp>) {
+          __obj_const_ptr = __ptr;
+        } else {
+          __obj_ptr = __ptr;
+        }
+      } else {
+        static_assert(is_function_v<_Tp>);
+        __fn_ptr = reinterpret_cast<void (*)()>(__ptr);
+      }
+    }
+  } __storage_;
+
+  template <class _Tp>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto __get(__storage_t __storage) {
+    if constexpr (is_object_v<_Tp>) {
+      if constexpr (is_const_v<_Tp>) {
+        return static_cast<_Tp*>(__storage.__obj_const_ptr);
+      } else {
+        return static_cast<_Tp*>(__storage.__obj_ptr);
+      }
+    } else {
+      static_assert(is_function_v<_Tp>);
+      return reinterpret_cast<_Tp*>(__storage.__fn_ptr);
+    }
+  }
+
+  using __call_t = _Rp (*)(__storage_t, _ArgTypes&&...) noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT);
+  __call_t __call_;
+
+public:
+  template <class _Fp>
+    requires is_function_v<_Fp> && __is_invocable_using<_Fp>
+  _LIBCPP_HIDE_FROM_ABI function_ref(_Fp* __fn_ptr) noexcept
+      : __storage_(__fn_ptr),
+        __call_([](__storage_t __storage, _ArgTypes&&... __args) static noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT) -> _Rp {
+          return __get<_Fp>(__storage)(std::forward<_ArgTypes>(__args)...);
+        }) {
+    _LIBCPP_ASSERT_UNCATEGORIZED(__fn_ptr != nullptr, "the function pointer should not be a nullptr");
+  }
+
+  template <class _Fp, class _Tp = remove_reference_t<_Fp>>
+    requires(!__is_function_ref<remove_cvref_t<_Fp>> && !is_member_pointer_v<_Tp> &&
+             __is_invocable_using<_LIBCPP_FUNCTION_REF_CV _Tp&>)
+  _LIBCPP_HIDE_FROM_ABI function_ref(_Fp&& __obj) noexcept
+      : __storage_(std::addressof(__obj)),
+        __call_([](__storage_t __storage, _ArgTypes&&... __args) static noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT) -> _Rp {
+          _LIBCPP_FUNCTION_REF_CV _Tp& __obj = *__get<_Tp>(__storage);
+          return __obj(std::forward<_ArgTypes>(__args)...);
+        }) {}
+
+  template <auto _Fn>
+    requires __is_invocable_using<decltype(_Fn)>
+  _LIBCPP_HIDE_FROM_ABI constexpr function_ref(nontype_t<_Fn>) noexcept
+      : __call_([](__storage_t, _ArgTypes&&... __args) static noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT) -> _Rp {
+          return std::invoke_r<_Rp>(_Fn, std::forward<_ArgTypes>(__args)...);
+        }) {
+    if constexpr (is_pointer_v<decltype(_Fn)> || is_member_pointer_v<decltype(_Fn)>) {
+      static_assert(_Fn != nullptr, "the function pointer should not be a nullptr");
+    }
+  }
+
+  template <auto _Fn, class _Up, class _Tp = remove_reference_t<_Up>>
+    requires(!is_rvalue_reference_v<_Up &&>) && __is_invocable_using<decltype(_Fn), _LIBCPP_FUNCTION_REF_CV _Tp&>
+  _LIBCPP_HIDE_FROM_ABI constexpr function_ref(nontype_t<_Fn>, _Up&& __obj) noexcept
+      : __storage_(std::addressof(__obj)),
+        __call_([](__storage_t __storage, _ArgTypes&&... __args) static noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT) -> _Rp {
+          _LIBCPP_FUNCTION_REF_CV _Tp& __obj = *__get<_Tp>(__storage);
+          return std::invoke_r<_Rp>(_Fn, __obj, std::forward<_ArgTypes>(__args)...);
+        }) {
+    if constexpr (is_pointer_v<decltype(_Fn)> || is_member_pointer_v<decltype(_Fn)>) {
+      static_assert(_Fn != nullptr, "the function pointer should not be a nullptr");
+    }
+  }
+
+  template <auto _Fn, class _Tp>
+    requires __is_invocable_using<decltype(_Fn), _LIBCPP_FUNCTION_REF_CV _Tp*>
+  _LIBCPP_HIDE_FROM_ABI constexpr function_ref(nontype_t<_Fn>, _LIBCPP_FUNCTION_REF_CV _Tp* __obj_ptr) noexcept
+      : __storage_(__obj_ptr),
+        __call_([](__storage_t __storage, _ArgTypes&&... __args) static noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT) -> _Rp {
+          auto __obj = __get<_LIBCPP_FUNCTION_REF_CV _Tp>(__storage);
+          return std::invoke_r<_Rp>(_Fn, __obj, std::forward<_ArgTypes>(__args)...);
+        }) {
+    if constexpr (is_pointer_v<decltype(_Fn)> || is_member_pointer_v<decltype(_Fn)>) {
+      static_assert(_Fn != nullptr, "the function pointer should not be a nullptr");
+    }
+
+    if constexpr (is_member_pointer_v<decltype(_Fn)>) {
+      _LIBCPP_ASSERT_UNCATEGORIZED(__obj_ptr != nullptr, "the object pointer should not be a nullptr");
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr function_ref(const function_ref&) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr function_ref& operator=(const function_ref&) noexcept = default;
+
+  template <class _Tp>
+    requires(!__is_function_ref<_Tp>) && (!is_pointer_v<_Tp>) && (!__is_nontype_t<_Tp>)
+  _LIBCPP_HIDE_FROM_ABI function_ref& operator=(_Tp) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _Rp operator()(_ArgTypes... __args) const noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT) {
+    return __call_(__storage_, std::forward<_ArgTypes>(__args)...);
+  }
+};
+
+template <class _Tp, class _Rp, class _Gp, class... _ArgTypes>
+struct __function_ref_bind<_Rp (_Gp::*)(_ArgTypes...) _LIBCPP_FUNCTION_REF_CV noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT),
+                           _Tp> {
+  using type = _Rp(_ArgTypes...) noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT);
+};
+
+template <class _Tp, class _Rp, class _Gp, class... _ArgTypes>
+struct __function_ref_bind<_Rp (_Gp::*)(_ArgTypes...) _LIBCPP_FUNCTION_REF_CV & noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT),
+                           _Tp> {
+  using type = _Rp(_ArgTypes...) noexcept(_LIBCPP_FUNCTION_REF_NOEXCEPT);
+};
+
+#endif // _LIBCPP_STD_VER >= 26
+
+_LIBCPP_END_NAMESPACE_STD

libcxx/include/__utility/nontype.h

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___UTILITY_NONTYPE_H
+#define _LIBCPP___UTILITY_NONTYPE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+template <auto _Vp>
+struct nontype_t {
+  _LIBCPP_HIDE_FROM_ABI explicit nontype_t() = default;
+};
+
+template <auto _Vp>
+inline constexpr nontype_t<_Vp> nontype{};
+
+template <class>
+inline constexpr bool __is_nontype_t = false;
+template <auto _Vp>
+inline constexpr bool __is_nontype_t<nontype_t<_Vp>> = true;
+
+#endif // _LIBCPP_STD_VER >= 26
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___UTILITY_NONTYPE_H

libcxx/include/functional

@@ -483,6 +483,11 @@ template <class  R, class ... ArgTypes>
 template <class  R, class ... ArgTypes>
   void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;
 
+// [func.wrap.ref], non-owning wrapper
+template<class... S> class function_ref;                              // freestanding, not defined, since C++26
+template<class R, class... ArgTypes>
+  class function_ref<R(ArgTypes...) cv noexcept(noex)>;               // freestanding, since C++26
+
 template <class T> struct hash;
 
 template <> struct hash<bool>;
@@ -541,6 +546,7 @@ POLICY:  For non-variadic implementations, the number of arguments is limited
 #include <__functional/compose.h>
 #include <__functional/default_searcher.h>
 #include <__functional/function.h>
+#include <__functional/function_ref.h>
 #include <__functional/hash.h>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>

libcxx/include/module.modulemap

@@ -1339,6 +1339,9 @@ module std_private_functional_compose                    [system] {
 }
 module std_private_functional_default_searcher           [system] { header "__functional/default_searcher.h" }
 module std_private_functional_function                   [system] { header "__functional/function.h" }
+module std_private_functional_function_ref               [system] { header "__functional/function_ref.h" }
+module std_private_functional_function_ref_common        [system] { textual header "__functional/function_ref_common.h" }
+module std_private_functional_function_ref_impl          [system] { textual header "__functional/function_ref_impl.h" }
 module std_private_functional_hash                       [system] {
   header "__functional/hash.h"
   export std_cstdint
@@ -2073,6 +2076,7 @@ module std_private_utility_move                   [system] {
   export std_private_type_traits_remove_reference
 }
 module std_private_utility_no_destroy             [system] { header "__utility/no_destroy.h" }
+module std_private_utility_nontype                [system] { header "__utility/nontype.h" }
 module std_private_utility_pair                   [system] {
   header "__utility/pair.h"
   export std_private_ranges_subrange_fwd