1fe6060f1SDimitry Andric //===----------------------------------------------------------------------===// 2fe6060f1SDimitry Andric // 3fe6060f1SDimitry Andric // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4fe6060f1SDimitry Andric // See https://llvm.org/LICENSE.txt for license information. 5fe6060f1SDimitry Andric // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6fe6060f1SDimitry Andric // 7fe6060f1SDimitry Andric //===----------------------------------------------------------------------===// 8fe6060f1SDimitry Andric 9fe6060f1SDimitry Andric #ifndef _LIBCPP___UTILITY_DECLVAL_H 10fe6060f1SDimitry Andric #define _LIBCPP___UTILITY_DECLVAL_H 11fe6060f1SDimitry Andric 12fe6060f1SDimitry Andric #include <__config> 13fe6060f1SDimitry Andric 14fe6060f1SDimitry Andric #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 15fe6060f1SDimitry Andric # pragma GCC system_header 16fe6060f1SDimitry Andric #endif 17fe6060f1SDimitry Andric 18fe6060f1SDimitry Andric _LIBCPP_BEGIN_NAMESPACE_STD 19fe6060f1SDimitry Andric 20fe6060f1SDimitry Andric // Suppress deprecation notice for volatile-qualified return type resulting 21fe6060f1SDimitry Andric // from volatile-qualified types _Tp. 22fe6060f1SDimitry Andric _LIBCPP_SUPPRESS_DEPRECATED_PUSH 23fe6060f1SDimitry Andric template <class _Tp> 24fe6060f1SDimitry Andric _Tp&& __declval(int); 25fe6060f1SDimitry Andric template <class _Tp> 26fe6060f1SDimitry Andric _Tp __declval(long); 27fe6060f1SDimitry Andric _LIBCPP_SUPPRESS_DEPRECATED_POP 28fe6060f1SDimitry Andric 29fe6060f1SDimitry Andric template <class _Tp> 30*5f757f3fSDimitry Andric _LIBCPP_HIDE_FROM_ABI decltype(std::__declval<_Tp>(0)) declval() _NOEXCEPT { 31*5f757f3fSDimitry Andric static_assert(!__is_same(_Tp, _Tp), 32*5f757f3fSDimitry Andric "std::declval can only be used in an unevaluated context. " 33*5f757f3fSDimitry Andric "It's likely that your current usage is trying to extract a value from the function."); 34*5f757f3fSDimitry Andric } 35fe6060f1SDimitry Andric 36fe6060f1SDimitry Andric _LIBCPP_END_NAMESPACE_STD 37fe6060f1SDimitry Andric 38fe6060f1SDimitry Andric #endif // _LIBCPP___UTILITY_DECLVAL_H 39