llvm-project/libcxx/include/__functional/reference_wrapper.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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_REFERENCE_WRAPPER_H
#define _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H

#include <__config>
#include <__functional/weak_result_type.h>
#include <__memory/addressof.h>
#include <__utility/forward.h>
#include <type_traits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
class _LIBCPP_TEMPLATE_VIS reference_wrapper : public __weak_result_type<_Tp>
{
public:
    // types
    typedef _Tp type;
private:
    type* __f_;

    static void __fun(_Tp&) _NOEXCEPT;
    static void __fun(_Tp&&) = delete;

public:
    template <class _Up, class = __enable_if_t<!__is_same_uncvref<_Up, reference_wrapper>::value, decltype(__fun(declval<_Up>())) > >
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
    reference_wrapper(_Up&& __u) _NOEXCEPT_(noexcept(__fun(declval<_Up>()))) {
        type& __f = static_cast<_Up&&>(__u);
        __f_ = _VSTD::addressof(__f);
    }

    // access
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
    operator type&() const _NOEXCEPT {return *__f_;}
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
    type& get() const _NOEXCEPT {return *__f_;}

    // invoke
    template <class... _ArgTypes>
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
    typename __invoke_of<type&, _ArgTypes...>::type
    operator() (_ArgTypes&&... __args) const {
        return std::__invoke(get(), std::forward<_ArgTypes>(__args)...);
    }
};

#if _LIBCPP_STD_VER > 14
template <class _Tp>
reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
#endif

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
reference_wrapper<_Tp>
ref(_Tp& __t) _NOEXCEPT
{
    return reference_wrapper<_Tp>(__t);
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
reference_wrapper<_Tp>
ref(reference_wrapper<_Tp> __t) _NOEXCEPT
{
    return __t;
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
reference_wrapper<const _Tp>
cref(const _Tp& __t) _NOEXCEPT
{
    return reference_wrapper<const _Tp>(__t);
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
reference_wrapper<const _Tp>
cref(reference_wrapper<_Tp> __t) _NOEXCEPT
{
    return __t;
}

template <class _Tp> void ref(const _Tp&&) = delete;
template <class _Tp> void cref(const _Tp&&) = delete;

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H