[libcxx-commits] [libcxx] [libc++] Implement `std::function_ref` (PR #186692)
Hristo Hristov via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Jul 30 22:53:21 PDT 2026
================
@@ -0,0 +1,201 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// This header is unguarded on purpose. This header is an implementation detail of function_ref.h
+// and generates multiple versions of std::function_ref
+
+#include <__assert>
+#include <__config>
+#include <__functional/function_ref_common.h>
+#include <__functional/invoke.h>
+#include <__memory/addressof.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/conjunction.h>
+#include <__type_traits/invoke.h>
+#include <__type_traits/is_const.h>
+#include <__type_traits/is_convertible.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_same.h>
+#include <__type_traits/is_void.h>
+#include <__type_traits/register_passable.h>
+#include <__type_traits/remove_cv.h>
+#include <__type_traits/remove_cvref.h>
+#include <__type_traits/remove_pointer.h>
+#include <__type_traits/remove_reference.h>
+#include <__utility/constant_wrapper.h>
+#include <__utility/forward.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+#ifndef _LIBCPP___FUNCTIONAL_FUNCTION_REF_H
+# error This header should only be included from function_ref.h
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+template <class...>
+class function_ref;
+
+template <bool _NoExcept1, bool _NoExcept2, class _Rp, class... _ArgTypes>
+struct __is_convertible_from_specialization<
+ function_ref<_Rp(_ArgTypes...) _LIBCPP_FUNCTION_REF_CV noexcept(_NoExcept1)>,
+ function_ref<_Rp(_ArgTypes...) const noexcept(_NoExcept2)> >
+ : is_convertible<_Rp (&)(_ArgTypes...) noexcept(_NoExcept2), _Rp (&)(_ArgTypes...) noexcept(_NoExcept1)> {};
+
+template <bool _NoExcept1, bool _NoExcept2, class _Rp, class... _ArgTypes>
+struct __is_convertible_from_specialization<
+ function_ref<_Rp(_ArgTypes...) _LIBCPP_FUNCTION_REF_CV noexcept(_NoExcept1)>,
+ function_ref<_Rp(_ArgTypes...) noexcept(_NoExcept2)> >
+ : _And<is_convertible<_Rp (&)(_ArgTypes...) noexcept(_NoExcept2), _Rp (&)(_ArgTypes...) noexcept(_NoExcept1)>,
+ is_convertible<_LIBCPP_FUNCTION_REF_CV int&, int&>> {};
+
+template <class _Rp, class... _ArgTypes, bool __is_noexcept>
+class function_ref<_Rp(_ArgTypes...) _LIBCPP_FUNCTION_REF_CV noexcept(__is_noexcept)> {
+private:
+ template <class... _Tp>
+ static constexpr bool __is_invocable_using =
+ _If<__is_noexcept, is_nothrow_invocable_r<_Rp, _Tp..., _ArgTypes...>, is_invocable_r<_Rp, _Tp..., _ArgTypes...>>::
+ value;
+
+ template <class _Fn2>
+ static constexpr bool __is_convertible_from_specialization_v =
+ __is_convertible_from_specialization<function_ref, _Fn2>::value;
+
+ template <class... _Tp>
+ friend class function_ref;
+
+ template <class _Arg>
+ using __arg_t _LIBCPP_NODEBUG = _If<__register_passable<_Arg>, _Arg, _Arg&&>;
+
+ using __storage_t _LIBCPP_NODEBUG = __function_ref_storage;
+
+ using __call_t _LIBCPP_NODEBUG = _Rp (*)(__storage_t, __arg_t<_ArgTypes>...) noexcept(__is_noexcept);
+
+ __storage_t __storage_;
+ __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, __arg_t<_ArgTypes>... __args) static noexcept(__is_noexcept) -> _Rp {
+ _Fp* __fn_ptr1 = __storage_t::template __get<_Fp>(__storage);
+ return std::invoke_r<_Rp>(__fn_ptr1, std::forward<__arg_t<_ArgTypes>>(__args)...);
+ }) {
+ _LIBCPP_ASSERT_NON_NULL(__fn_ptr != nullptr, "the function pointer should not be a nullptr");
+ }
+
+ template <class _Fn, class _Tp = remove_reference_t<_Fn>>
+ requires(!is_same_v<remove_cvref_t<_Fn>, function_ref> && !is_member_pointer_v<_Tp> &&
+ __is_invocable_using<_LIBCPP_FUNCTION_REF_CV _Tp&> && !__is_convertible_from_specialization_v<_Tp>)
+ _LIBCPP_HIDE_FROM_ABI constexpr function_ref(_Fn&& __obj) noexcept {
+ using _Dn = remove_cv_t<_Tp>;
+ if constexpr (__statically_callable<_Dn, __arg_t<_ArgTypes>...>) {
+ __call_ = [](__storage_t, __arg_t<_ArgTypes>... __args) static noexcept(__is_noexcept) -> _Rp {
+ return _Dn::operator()(std::forward<__arg_t<_ArgTypes>>(__args)...);
+ };
+ } else {
+ __storage_ = __storage_t(std::addressof(__obj)),
+ __call_ = [](__storage_t __storage, __arg_t<_ArgTypes>... __args) static noexcept(__is_noexcept) -> _Rp {
+ _LIBCPP_FUNCTION_REF_CV _Tp& __obj1 = *__storage_t::template __get<_Tp>(__storage);
+ return std::invoke_r<_Rp>(__obj1, std::forward<__arg_t<_ArgTypes>>(__args)...);
+ };
+ }
+ }
+
+ template <class _Fn, class _Tp = remove_reference_t<_Fn>>
+ requires(!is_same_v<remove_cvref_t<_Fn>, function_ref> && !is_member_pointer_v<_Tp> &&
+ __is_invocable_using<_LIBCPP_FUNCTION_REF_CV _Tp&> && __is_convertible_from_specialization_v<_Tp>)
+ _LIBCPP_HIDE_FROM_ABI constexpr function_ref(_Fn&& __obj) noexcept
+ : __storage_(__obj.__storage_), __call_(__obj.__call_) {}
+
+ template <auto _Cw, class _Fn>
+ requires __is_invocable_using<const _Fn&>
+ _LIBCPP_HIDE_FROM_ABI constexpr function_ref(constant_wrapper<_Cw, _Fn> __f) noexcept
+ : __call_([](__storage_t, __arg_t<_ArgTypes>... __args) static noexcept(__is_noexcept) -> _Rp {
+ return std::invoke_r<_Rp>(decltype(__f)::value, std::forward<__arg_t<_ArgTypes>>(__args)...);
+ }) {
+ if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>) {
+ static_assert(__f.value != nullptr, "the function pointer should not be a nullptr");
+ }
+ if constexpr (sizeof...(_ArgTypes) > 0 && (__constexpr_param<remove_cvref_t<_ArgTypes>> && ...)) {
+ static_assert(
+ !requires {
+ typename constant_wrapper<std::invoke(decltype(__f)::value, remove_cvref_t<_ArgTypes>::value...)>;
+ },
+ "cw(args...) should be equivalent to fn(args...), otherwise the intended behavior for a function_ref "
+ "constructed from cw would be ambiguous");
+ }
+ }
+
+ template <auto _Cw, class _Fn, class _Up, class _Tp = remove_reference_t<_Up>>
+ requires(!is_rvalue_reference_v<_Up &&>) && __is_invocable_using<const _Fn&, _LIBCPP_FUNCTION_REF_CV _Tp&>
+ _LIBCPP_HIDE_FROM_ABI constexpr function_ref(constant_wrapper<_Cw, _Fn> __f, _Up&& __obj) noexcept
+ : __storage_(std::addressof(__obj)),
+ __call_([](__storage_t __storage, __arg_t<_ArgTypes>... __args) static noexcept(__is_noexcept) -> _Rp {
+ auto& __obj1 = static_cast<_LIBCPP_FUNCTION_REF_CV _Tp&>(*__storage_t::template __get<_Tp>(__storage));
+ return std::invoke_r<_Rp>(decltype(__f)::value, __obj1, std::forward<__arg_t<_ArgTypes>>(__args)...);
+ }) {
+ if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>) {
+ static_assert(__f.value != nullptr, "the function pointer should not be a nullptr");
+ }
+ }
+
+ template <auto _Cw, class _Fn, class _Tp>
+ requires __is_invocable_using<const _Fn&, _LIBCPP_FUNCTION_REF_CV _Tp*>
+ _LIBCPP_HIDE_FROM_ABI constexpr function_ref(constant_wrapper<_Cw, _Fn> __f,
+ _LIBCPP_FUNCTION_REF_CV _Tp* __obj_ptr) noexcept
+ : __storage_(__obj_ptr),
+ __call_([](__storage_t __storage, __arg_t<_ArgTypes>... __args) static noexcept(__is_noexcept) -> _Rp {
+ auto* __obj = __storage_t::template __get<_LIBCPP_FUNCTION_REF_CV _Tp>(__storage);
+ return std::invoke_r<_Rp>(decltype(__f)::value, __obj, std::forward<__arg_t<_ArgTypes>>(__args)...);
+ }) {
+ if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>) {
+ static_assert(__f.value != nullptr, "the function pointer should not be a nullptr");
+ }
+
+ if constexpr (is_member_pointer_v<_Fn>) {
+ _LIBCPP_ASSERT_NON_NULL(__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_convertible_from_specialization_v<_Tp>) && (!is_pointer_v<_Tp>) && (!__is_constant_wrapper<_Tp>)
+ _LIBCPP_HIDE_FROM_ABI function_ref& operator=(_Tp) = delete;
+
+ _LIBCPP_HIDE_FROM_ABI _Rp operator()(_ArgTypes... __args) const noexcept(__is_noexcept) {
----------------
Zingam wrote:
@huixie90 Should this operator be marked `[[nodiscard]]`?
https://github.com/llvm/llvm-project/pull/186692
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