libcxx/include/__concepts/convertible_to.h

   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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___CONCEPTS_CONVERTIBLE_TO_H
  10 #define _LIBCPP___CONCEPTS_CONVERTIBLE_TO_H
  11
  12 #include <__config>
  13 #include <type_traits>
  14
  15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  16 #pragma GCC system_header
  17 #endif
  18
  19 _LIBCPP_BEGIN_NAMESPACE_STD
  20
  21 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  22
  23 // [concept.convertible]
  24
  25 template<class _From, class _To>
  26 concept convertible_to =
  27   is_convertible_v<_From, _To> &&
  28   requires (add_rvalue_reference_t<_From> (&__f)()) {
  29     static_cast<_To>(__f());
  30   };
  31
  32 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  33
  34 _LIBCPP_END_NAMESPACE_STD
  35
  36 #endif // _LIBCPP___CONCEPTS_CONVERTIBLE_TO_H