[libc++] Implement std::move_only_function (P0288R9) #94670
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| Original file line number | Diff line number | Diff line change |
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| //===----------------------------------------------------------------------===// | ||
| // | ||
| // 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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #ifndef _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H | ||
| #define _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H | ||
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| #include <__config> | ||
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| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) | ||
| # pragma GCC system_header | ||
| #endif | ||
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| #if _LIBCPP_STD_VER >= 23 && !defined(_LIBCPP_COMPILER_GCC) && _LIBCPP_HAS_EXPERIMENTAL_MOVE_ONLY_FUNCTION | ||
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| // move_only_function design: | ||
| // | ||
| // move_only_function has a small buffer with a size of `3 * sizeof(void*)` bytes. This buffer can only be used when the | ||
| // object to be stored is "trivially relocatable" (currently only when it is trivially move constructible and trivially | ||
| // destructible). The vtable entry for the destructor is a null pointer when the stored object is trivially | ||
| // destructible. | ||
| // | ||
| // trivially relocatable: It would also be possible to store nothrow_move_constructible types, but that would mean | ||
| // that move_only_function itself would not be trivially relocatable anymore. The decision to keep move_only_function | ||
| // trivially relocatable was made because we expect move_only_function to be stored persistently most of the time, since | ||
| // std::function_ref can be used for cases where a function object doesn't need to be stored. | ||
| // | ||
| // buffer size: We did a survey of six implementations from various vendors. Three of them had a buffer size of 24 bytes | ||
| // on 64 bit systems. This will also allow storing a function object containing a std::string or std::vector inside the | ||
| // small buffer once there is a language definition of "trivially relocatable". | ||
| // | ||
| // interaction with copyable_function: When converting a copyable_function into a move_only_function we want to avoid | ||
| // wrapping the copyable_function inside the move_only_function to avoid a double indirection. Instead, we copy the | ||
| // small buffer and use copyable_function's vtable. | ||
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| // NOLINTBEGIN(readability-duplicate-include) | ||
| # define _LIBCPP_IN_MOVE_ONLY_FUNCTION_H | ||
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| # include <__functional/move_only_function_impl.h> | ||
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| # define _LIBCPP_MOVE_ONLY_FUNCTION_REF & | ||
| # include <__functional/move_only_function_impl.h> | ||
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| # define _LIBCPP_MOVE_ONLY_FUNCTION_REF && | ||
| # include <__functional/move_only_function_impl.h> | ||
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| # define _LIBCPP_MOVE_ONLY_FUNCTION_CV const | ||
| # include <__functional/move_only_function_impl.h> | ||
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| # define _LIBCPP_MOVE_ONLY_FUNCTION_CV const | ||
| # define _LIBCPP_MOVE_ONLY_FUNCTION_REF & | ||
| # include <__functional/move_only_function_impl.h> | ||
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| # define _LIBCPP_MOVE_ONLY_FUNCTION_CV const | ||
| # define _LIBCPP_MOVE_ONLY_FUNCTION_REF && | ||
| # include <__functional/move_only_function_impl.h> | ||
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| # undef _LIBCPP_IN_MOVE_ONLY_FUNCTION_H | ||
| // NOLINTEND(readability-duplicate-include) | ||
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| #endif // _LIBCPP_STD_VER >= 23 && !defined(_LIBCPP_COMPILER_GCC) && _LIBCPP_HAS_EXPERIMENTAL_MOVE_ONLY_FUNCTION | ||
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| #endif // _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H |
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| @@ -0,0 +1,44 @@ | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // 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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #ifndef _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H | ||
| #define _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H | ||
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| #include <__config> | ||
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| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) | ||
| # pragma GCC system_header | ||
| #endif | ||
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| #if _LIBCPP_STD_VER >= 23 && _LIBCPP_HAS_EXPERIMENTAL_MOVE_ONLY_FUNCTION | ||
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| _LIBCPP_BEGIN_NAMESPACE_STD | ||
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| template <class...> | ||
| class move_only_function; | ||
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| template <class> | ||
| inline constexpr bool __is_move_only_function_v = false; | ||
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| template <class... _Args> | ||
| inline constexpr bool __is_move_only_function_v<move_only_function<_Args...>> = true; | ||
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| template <class _BufferT, class _ReturnT, class... _ArgTypes> | ||
| struct _MoveOnlyFunctionVTable { | ||
| using _CallFunc _LIBCPP_NODEBUG = _ReturnT(_BufferT&, _ArgTypes...); | ||
| using _DestroyFunc _LIBCPP_NODEBUG = void(_BufferT&) noexcept; | ||
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| _CallFunc* __call_; | ||
| _DestroyFunc* __destroy_; | ||
| }; | ||
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| _LIBCPP_END_NAMESPACE_STD | ||
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| #endif // _LIBCPP_STD_VER >= 23 && _LIBCPP_HAS_EXPERIMENTAL_MOVE_ONLY_FUNCTION | ||
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| #endif // _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H |
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| @@ -0,0 +1,224 @@ | ||||||||
| //===----------------------------------------------------------------------===// | ||||||||
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| // | ||||||||
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. | ||||||||
| // See https://llvm.org/LICENSE.txt for license information. | ||||||||
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Member
There was a problem hiding this comment. Note to self: we stopped while we were talking about whether we need |
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| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception | ||||||||
| // | ||||||||
| //===----------------------------------------------------------------------===// | ||||||||
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| // This header is unguarded on purpose. This header is an implementation detail of move_only_function.h | ||||||||
| // and generates multiple versions of std::move_only_function | ||||||||
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| #include <__assert> | ||||||||
| #include <__config> | ||||||||
| #include <__cstddef/nullptr_t.h> | ||||||||
| #include <__cstddef/size_t.h> | ||||||||
| #include <__functional/invoke.h> | ||||||||
| #include <__functional/move_only_function_common.h> | ||||||||
| #include <__memory/addressof.h> | ||||||||
| #include <__memory/construct_at.h> | ||||||||
| #include <__type_traits/decay.h> | ||||||||
| #include <__type_traits/invoke.h> | ||||||||
| #include <__type_traits/is_constructible.h> | ||||||||
| #include <__type_traits/is_function.h> | ||||||||
| #include <__type_traits/is_member_pointer.h> | ||||||||
| #include <__type_traits/is_pointer.h> | ||||||||
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| #include <__type_traits/is_same.h> | ||||||||
| #include <__type_traits/is_trivially_destructible.h> | ||||||||
| #include <__type_traits/remove_cvref.h> | ||||||||
| #include <__type_traits/remove_pointer.h> | ||||||||
| #include <__utility/exchange.h> | ||||||||
| #include <__utility/forward.h> | ||||||||
| #include <__utility/in_place.h> | ||||||||
| #include <__utility/move.h> | ||||||||
| #include <__utility/small_buffer.h> | ||||||||
| #include <__utility/swap.h> | ||||||||
| #include <initializer_list> | ||||||||
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| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) | ||||||||
| # pragma GCC system_header | ||||||||
| #endif | ||||||||
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| #ifndef _LIBCPP_IN_MOVE_ONLY_FUNCTION_H | ||||||||
| # error This header should only be included from move_only_function.h | ||||||||
| #endif | ||||||||
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| #ifndef _LIBCPP_MOVE_ONLY_FUNCTION_CV | ||||||||
| # define _LIBCPP_MOVE_ONLY_FUNCTION_CV | ||||||||
| #endif | ||||||||
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| #ifndef _LIBCPP_MOVE_ONLY_FUNCTION_REF | ||||||||
| # define _LIBCPP_MOVE_ONLY_FUNCTION_REF | ||||||||
| # define _LIBCPP_MOVE_ONLY_FUNCTION_INVOKE_QUALS _LIBCPP_MOVE_ONLY_FUNCTION_CV& | ||||||||
| #else | ||||||||
| # define _LIBCPP_MOVE_ONLY_FUNCTION_INVOKE_QUALS _LIBCPP_MOVE_ONLY_FUNCTION_CV _LIBCPP_MOVE_ONLY_FUNCTION_REF | ||||||||
| #endif | ||||||||
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| #define _LIBCPP_MOVE_ONLY_FUNCTION_CVREF _LIBCPP_MOVE_ONLY_FUNCTION_CV _LIBCPP_MOVE_ONLY_FUNCTION_REF | ||||||||
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| _LIBCPP_PUSH_MACROS | ||||||||
| #include <__undef_macros> | ||||||||
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| _LIBCPP_BEGIN_NAMESPACE_STD | ||||||||
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| template <class...> | ||||||||
| class move_only_function; | ||||||||
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| template <class _ReturnT, class... _ArgTypes, bool __is_noexcept> | ||||||||
| class [[_Clang::__trivial_abi__]] | ||||||||
| move_only_function<_ReturnT(_ArgTypes...) _LIBCPP_MOVE_ONLY_FUNCTION_CVREF noexcept(__is_noexcept)> { | ||||||||
| private: | ||||||||
| static constexpr size_t __buffer_size_ = 3 * sizeof(void*); | ||||||||
| static constexpr size_t __buffer_alignment_ = alignof(void*); | ||||||||
| using _BufferT _LIBCPP_NODEBUG = __small_buffer<__buffer_size_, __buffer_alignment_>; | ||||||||
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| using _VTable _LIBCPP_NODEBUG = _MoveOnlyFunctionVTable<_BufferT, _ReturnT, _ArgTypes...>; | ||||||||
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| template <class _Functor> | ||||||||
| static constexpr _VTable __vtable_var_ = { | ||||||||
| .__call_ = [](_BufferT& __buffer, _ArgTypes... __args) noexcept(__is_noexcept) -> _ReturnT { | ||||||||
| return std::invoke_r<_ReturnT>( | ||||||||
| static_cast<_Functor _LIBCPP_MOVE_ONLY_FUNCTION_INVOKE_QUALS>(*__buffer.__get<_Functor>()), | ||||||||
| std::forward<_ArgTypes>(__args)...); | ||||||||
| }, | ||||||||
| .__destroy_ = (_BufferT::__fits_in_buffer<_Functor> && is_trivially_destructible_v<_Functor>) | ||||||||
| ? nullptr | ||||||||
| : [](_BufferT& __buffer) noexcept -> void { | ||||||||
| std::destroy_at(__buffer.__get<_Functor>()); | ||||||||
| __buffer.__dealloc<_Functor>(); | ||||||||
| }}; | ||||||||
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| template <class _VT> | ||||||||
| static constexpr bool __is_callable_from = [] { | ||||||||
| using _DVT = decay_t<_VT>; | ||||||||
| if constexpr (__is_noexcept) { | ||||||||
| return is_nothrow_invocable_r_v<_ReturnT, _DVT _LIBCPP_MOVE_ONLY_FUNCTION_CVREF, _ArgTypes...> && | ||||||||
| is_nothrow_invocable_r_v<_ReturnT, _DVT _LIBCPP_MOVE_ONLY_FUNCTION_INVOKE_QUALS, _ArgTypes...>; | ||||||||
| } else { | ||||||||
| return is_invocable_r_v<_ReturnT, _DVT _LIBCPP_MOVE_ONLY_FUNCTION_CVREF, _ArgTypes...> && | ||||||||
| is_invocable_r_v<_ReturnT, _DVT _LIBCPP_MOVE_ONLY_FUNCTION_INVOKE_QUALS, _ArgTypes...>; | ||||||||
| } | ||||||||
| }(); | ||||||||
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| template <class _Func, class... _Args> | ||||||||
| _LIBCPP_HIDE_FROM_ABI void __construct(_Args&&... __args) { | ||||||||
| static_assert(is_constructible_v<decay_t<_Func>, _Func>); | ||||||||
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| using _StoredFunc = decay_t<_Func>; | ||||||||
| __vtable_ = std::addressof(__vtable_var_<_StoredFunc>); | ||||||||
| __buffer_.__construct<_StoredFunc>(std::forward<_Args>(__args)...); | ||||||||
| } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI void __reset() noexcept { | ||||||||
| if (__vtable_ && __vtable_->__destroy_) | ||||||||
| __vtable_->__destroy_(__buffer_); | ||||||||
| __vtable_ = nullptr; | ||||||||
| } | ||||||||
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| public: | ||||||||
| using result_type = _ReturnT; | ||||||||
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| // [func.wrap.move.ctor] | ||||||||
| move_only_function() noexcept = default; | ||||||||
| _LIBCPP_HIDE_FROM_ABI move_only_function(nullptr_t) noexcept {} | ||||||||
| _LIBCPP_HIDE_FROM_ABI move_only_function(move_only_function&& __other) noexcept | ||||||||
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Member
There was a problem hiding this comment. Please make sure you have a test for the noexceptness (and the non-noexceptness) of every function. |
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| : __vtable_(__other.__vtable_), __buffer_(std::move(__other.__buffer_)) { | ||||||||
| __other.__vtable_ = nullptr; | ||||||||
| } | ||||||||
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| template <class _Func> | ||||||||
| requires(!is_same_v<remove_cvref_t<_Func>, move_only_function> && !__is_inplace_type<_Func>::value && | ||||||||
| __is_callable_from<_Func>) | ||||||||
| _LIBCPP_HIDE_FROM_ABI move_only_function(_Func&& __func) noexcept { | ||||||||
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Member
There was a problem hiding this comment. Why is this noexcept? That seems wrong. This also needs a test. |
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| using _StoredFunc = decay_t<_Func>; | ||||||||
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| if constexpr ((is_pointer_v<_StoredFunc> && is_function_v<remove_pointer_t<_StoredFunc>>) || | ||||||||
| is_member_function_pointer_v<_StoredFunc>) { | ||||||||
| if (__func != nullptr) { | ||||||||
| __vtable_ = std::addressof(__vtable_var_<_StoredFunc>); | ||||||||
| static_assert(_BufferT::__fits_in_buffer<_StoredFunc>); | ||||||||
| __buffer_.__construct<_StoredFunc>(std::forward<_Func>(__func)); | ||||||||
| } | ||||||||
| } else if constexpr (__is_move_only_function_v<_StoredFunc>) { | ||||||||
| if (__func) { | ||||||||
| __vtable_ = std::exchange(__func.__vtable_, nullptr); | ||||||||
| __buffer_ = std::move(__func.__buffer_); | ||||||||
| } | ||||||||
| } else { | ||||||||
| __construct<_Func>(std::forward<_Func>(__func)); | ||||||||
| } | ||||||||
| } | ||||||||
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| template <class _Func, class... _Args> | ||||||||
| requires is_constructible_v<decay_t<_Func>, _Args...> && __is_callable_from<_Func> | ||||||||
| _LIBCPP_HIDE_FROM_ABI explicit move_only_function(in_place_type_t<_Func>, _Args&&... __args) { | ||||||||
| static_assert(is_same_v<decay_t<_Func>, _Func>); | ||||||||
| __construct<_Func>(std::forward<_Args>(__args)...); | ||||||||
| } | ||||||||
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| template <class _Func, class _InitListType, class... _Args> | ||||||||
| requires is_constructible_v<decay_t<_Func>, initializer_list<_InitListType>&, _Args...> && __is_callable_from<_Func> | ||||||||
| _LIBCPP_HIDE_FROM_ABI explicit move_only_function( | ||||||||
| in_place_type_t<_Func>, initializer_list<_InitListType> __il, _Args&&... __args) { | ||||||||
| static_assert(is_same_v<decay_t<_Func>, _Func>); | ||||||||
| __construct<_Func>(__il, std::forward<_Args>(__args)...); | ||||||||
| } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI move_only_function& operator=(move_only_function&& __other) noexcept { | ||||||||
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Member
There was a problem hiding this comment.
Suggested change
Also, with a test |
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| move_only_function(std::move(__other)).swap(*this); | ||||||||
| return *this; | ||||||||
| } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI move_only_function& operator=(nullptr_t) noexcept { | ||||||||
| __reset(); | ||||||||
| return *this; | ||||||||
| } | ||||||||
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| template <class _Func> | ||||||||
| requires(!is_same_v<remove_cvref_t<_Func>, move_only_function> && !__is_inplace_type<_Func>::value && | ||||||||
| __is_callable_from<_Func>) | ||||||||
| _LIBCPP_HIDE_FROM_ABI move_only_function& operator=(_Func&& __func) { | ||||||||
| move_only_function(std::forward<_Func>(__func)).swap(*this); | ||||||||
| return *this; | ||||||||
| } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI ~move_only_function() { __reset(); } | ||||||||
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| // [func.wrap.move.inv] | ||||||||
| _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept { return __vtable_; } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI _ReturnT operator()(_ArgTypes... __args) _LIBCPP_MOVE_ONLY_FUNCTION_CVREF | ||||||||
| noexcept(__is_noexcept) { | ||||||||
| _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(static_cast<bool>(*this), "Tried to call a disengaged move_only_function"); | ||||||||
| const auto __call = static_cast<_ReturnT (*)(_BufferT&, _ArgTypes...)>(__vtable_->__call_); | ||||||||
| return __call(__buffer_, std::forward<_ArgTypes>(__args)...); | ||||||||
| } | ||||||||
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| // [func.wrap.move.util] | ||||||||
| _LIBCPP_HIDE_FROM_ABI void swap(move_only_function& __other) noexcept { | ||||||||
| std::swap(__vtable_, __other.__vtable_); | ||||||||
| std::swap(__buffer_, __other.__buffer_); | ||||||||
| } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI friend void swap(move_only_function& __lhs, move_only_function& __rhs) noexcept { | ||||||||
| __lhs.swap(__rhs); | ||||||||
| } | ||||||||
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| _LIBCPP_HIDE_FROM_ABI friend bool operator==(const move_only_function& __func, nullptr_t) noexcept { return !__func; } | ||||||||
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| private: | ||||||||
| const _VTable* __vtable_ = nullptr; | ||||||||
| mutable _BufferT __buffer_; | ||||||||
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Member
There was a problem hiding this comment. I though unlike |
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| template <class...> | ||||||||
| friend class move_only_function; | ||||||||
| }; | ||||||||
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| #undef _LIBCPP_MOVE_ONLY_FUNCTION_CV | ||||||||
| #undef _LIBCPP_MOVE_ONLY_FUNCTION_REF | ||||||||
| #undef _LIBCPP_MOVE_ONLY_FUNCTION_INVOKE_QUALS | ||||||||
| #undef _LIBCPP_MOVE_ONLY_FUNCTION_CVREF | ||||||||
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| _LIBCPP_END_NAMESPACE_STD | ||||||||
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| _LIBCPP_POP_MACROS | ||||||||
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