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// Implementation of std::move_only_function -*- C++ -*-
// Copyright The GNU Toolchain Authors.
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <>.
/** @file include/bits/mofunc_impl.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{functional}
# define _GLIBCXX_MOF_CV
namespace std _GLIBCXX_VISIBILITY(default)
* @brief Polymorphic function wrapper.
* @ingroup functors
* @since C++23
* @headerfile functional
* The `std::move_only_function` class template is a call wrapper similar
* to * `std::function`, but does not require the stored target function
* to be copyable.
* It also supports const-qualification, ref-qualification, and
* no-throw guarantees. The qualifications and exception-specification
* of the `move_only_function::operator()` member function are respected
* when invoking the target function.
template<typename _Res, typename... _ArgTypes, bool _Noex>
class move_only_function<_Res(_ArgTypes...) _GLIBCXX_MOF_CV
_GLIBCXX_MOF_REF noexcept(_Noex)>
: _Mofunc_base
template<typename _Tp>
using __callable
= __conditional_t<_Noex,
is_nothrow_invocable_r<_Res, _Tp, _ArgTypes...>,
is_invocable_r<_Res, _Tp, _ArgTypes...>>;
// []/1 is-callable-from<VT>
template<typename _Vt>
static constexpr bool __is_callable_from
= __and_v<__callable<_Vt _GLIBCXX_MOF_CV_REF>,
__callable<_Vt _GLIBCXX_MOF_INV_QUALS>>;
using result_type = _Res;
/// Creates an empty object.
move_only_function() noexcept { }
/// Creates an empty object.
move_only_function(nullptr_t) noexcept { }
/// Moves the target object, leaving the source empty.
move_only_function(move_only_function&& __x) noexcept
: _Mofunc_base(static_cast<_Mofunc_base&&>(__x)),
_M_invoke(std::__exchange(__x._M_invoke, nullptr))
{ }
/// Stores a target object initialized from the argument.
template<typename _Fn, typename _Vt = decay_t<_Fn>>
requires (!is_same_v<_Vt, move_only_function>)
&& (!__is_in_place_type_v<_Vt>) && __is_callable_from<_Vt>
move_only_function(_Fn&& __f) noexcept(_S_nothrow_init<_Vt, _Fn>())
if constexpr (is_function_v<remove_pointer_t<_Vt>>
|| is_member_pointer_v<_Vt>
|| __is_move_only_function_v<_Vt>)
if (__f == nullptr)
_M_invoke = &_S_invoke<_Vt>;
/// Stores a target object initialized from the arguments.
template<typename _Tp, typename... _Args>
requires is_constructible_v<_Tp, _Args...>
&& __is_callable_from<_Tp>
move_only_function(in_place_type_t<_Tp>, _Args&&... __args)
noexcept(_S_nothrow_init<_Tp, _Args...>())
: _M_invoke(&_S_invoke<_Tp>)
static_assert(is_same_v<decay_t<_Tp>, _Tp>);
/// Stores a target object initialized from the arguments.
template<typename _Tp, typename _Up, typename... _Args>
requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
&& __is_callable_from<_Tp>
move_only_function(in_place_type_t<_Tp>, initializer_list<_Up> __il,
_Args&&... __args)
noexcept(_S_nothrow_init<_Tp, initializer_list<_Up>&, _Args...>())
: _M_invoke(&_S_invoke<_Tp>)
static_assert(is_same_v<decay_t<_Tp>, _Tp>);
_M_init<_Tp>(__il, std::forward<_Args>(__args)...);
/// Stores a new target object, leaving `x` empty.
operator=(move_only_function&& __x) noexcept
_M_invoke = std::__exchange(__x._M_invoke, nullptr);
return *this;
/// Destroys the target object (if any).
operator=(nullptr_t) noexcept
_M_invoke = nullptr;
return *this;
/// Stores a new target object, initialized from the argument.
template<typename _Fn>
requires is_constructible_v<move_only_function, _Fn>
operator=(_Fn&& __f)
noexcept(is_nothrow_constructible_v<move_only_function, _Fn>)
return *this;
~move_only_function() = default;
/// True if a target object is present, false otherwise.
explicit operator bool() const noexcept { return _M_invoke != nullptr; }
/** Invoke the target object.
* The target object will be invoked using the supplied arguments,
* and as an lvalue or rvalue, and as const or non-const, as dictated
* by the template arguments of the `move_only_function` specialization.
* @pre Must not be empty.
operator()(_ArgTypes... __args) _GLIBCXX_MOF_CV_REF noexcept(_Noex)
__glibcxx_assert(*this != nullptr);
return _M_invoke(this, std::forward<_ArgTypes>(__args)...);
/// Exchange the target objects (if any).
swap(move_only_function& __x) noexcept
std::swap(_M_invoke, __x._M_invoke);
/// Exchange the target objects (if any).
friend void
swap(move_only_function& __x, move_only_function& __y) noexcept
{ __x.swap(__y); }
/// Check for emptiness by comparing with `nullptr`.
friend bool
operator==(const move_only_function& __x, nullptr_t) noexcept
{ return __x._M_invoke == nullptr; }
template<typename _Tp>
using __param_t = __conditional_t<is_scalar_v<_Tp>, _Tp, _Tp&&>;
using _Invoker = _Res (*)(_Mofunc_base _GLIBCXX_MOF_CV*,
__param_t<_ArgTypes>...) noexcept(_Noex);
template<typename _Tp>
static _Res
_S_invoke(_Mofunc_base _GLIBCXX_MOF_CV* __self,
__param_t<_ArgTypes>... __args) noexcept(_Noex)
using _TpCv = _Tp _GLIBCXX_MOF_CV;
using _TpInv = _Tp _GLIBCXX_MOF_INV_QUALS;
return std::__invoke_r<_Res>(
_Invoker _M_invoke = nullptr;
} // namespace std