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___TYPE_TRAITS_IS_CORE_CONVERTIBLE_H
10 #define _LIBCPP___TYPE_TRAITS_IS_CORE_CONVERTIBLE_H
11 
12 #include <__config>
13 #include <__type_traits/integral_constant.h>
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 // [conv.general]/3 says "E is convertible to T" whenever "T t=E;" is well-formed.
22 // We can't test for that, but we can test implicit convertibility by passing it
23 // to a function. Notice that __is_core_convertible<void,void> is false,
24 // and __is_core_convertible<immovable-type,immovable-type> is true in C++17 and later.
25 
26 template <class _Tp, class _Up, class = void>
27 struct __is_core_convertible : public false_type {};
28 
29 template <class _Tp, class _Up>
30 struct __is_core_convertible<_Tp, _Up, decltype(
31     static_cast<void(*)(_Up)>(0) ( static_cast<_Tp(*)()>(0)() )
32 )> : public true_type {};
33 
34 _LIBCPP_END_NAMESPACE_STD
35 
36 #endif // _LIBCPP___TYPE_TRAITS_IS_CORE_CONVERTIBLE_H
37