libc/src/__support/CPP/utility/declval.h

   1 //===-- declval utility -----------------------------------------*- C++ -*-===//
   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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_UTILITY_DECLVAL_H
   9 #define LLVM_LIBC_SRC___SUPPORT_CPP_UTILITY_DECLVAL_H
  10
  11 #include "src/__support/CPP/type_traits/add_rvalue_reference.h"
  12 #include "src/__support/CPP/type_traits/always_false.h"
  13 #include "src/__support/macros/config.h"
  14
  15 namespace LIBC_NAMESPACE_DECL {
  16 namespace cpp {
  17
  18 // declval
  19 template <typename T> cpp::add_rvalue_reference_t<T> declval() {
  20   static_assert(cpp::always_false<T>,
  21                 "declval not allowed in an evaluated context");
  22 }
  23
  24 } // namespace cpp
  25 } // namespace LIBC_NAMESPACE_DECL
  26
  27 #endif // LLVM_LIBC_SRC___SUPPORT_CPP_UTILITY_DECLVAL_H