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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___UTILITY_DECLVAL_H10#define _LIBCPP___UTILITY_DECLVAL_H11 12#include <__config>13 14#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)15# pragma GCC system_header16#endif17 18_LIBCPP_BEGIN_NAMESPACE_STD19 20// Suppress deprecation notice for volatile-qualified return type resulting21// from volatile-qualified types _Tp.22_LIBCPP_SUPPRESS_DEPRECATED_PUSH23template <class _Tp>24_Tp&& __declval(int);25template <class _Tp>26_Tp __declval(long);27_LIBCPP_SUPPRESS_DEPRECATED_POP28 29template <class _Tp>30_LIBCPP_HIDE_FROM_ABI decltype(std::__declval<_Tp>(0)) declval() _NOEXCEPT {31 static_assert(!__is_same(_Tp, _Tp),32 "std::declval can only be used in an unevaluated context. "33 "It's likely that your current usage is trying to extract a value from the function.");34}35 36_LIBCPP_END_NAMESPACE_STD37 38#endif // _LIBCPP___UTILITY_DECLVAL_H39