1 // -*- C++ -*-
2 //===----------------------------------------------------------------------===//
3 //
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef _LIBCPP___FORMAT_CONCEPTS_H
11 #define _LIBCPP___FORMAT_CONCEPTS_H
12 
13 #include <__concepts/same_as.h>
14 #include <__concepts/semiregular.h>
15 #include <__config>
16 #include <__format/format_fwd.h>
17 #include <__format/format_parse_context.h>
18 #include <type_traits>
19 
20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
21 #  pragma GCC system_header
22 #endif
23 
24 _LIBCPP_BEGIN_NAMESPACE_STD
25 
26 #if _LIBCPP_STD_VER > 17
27 
28 // The output iterator isn't specified. A formatter should accept any
29 // output_iterator. This iterator is a minimal iterator to test the concept.
30 // (Note testing for (w)format_context would be a valid choice, but requires
31 // selecting the proper one depending on the type of _CharT.)
32 template <class _CharT>
33 using __fmt_iter_for = _CharT*;
34 
35 // The concept is based on P2286R6
36 // It lacks the const of __cf as required by, the not yet accepted, LWG-3636.
37 // The current formatters can't be easily adapted, but that is WIP.
38 // TODO FMT properly implement this concepts once accepted.
39 template <class _Tp, class _CharT>
40 concept __formattable = (semiregular<formatter<remove_cvref_t<_Tp>, _CharT>>) &&
41                         requires(formatter<remove_cvref_t<_Tp>, _CharT> __f,
42                                  formatter<remove_cvref_t<_Tp>, _CharT> __cf, _Tp __t,
43                                  basic_format_context<__fmt_iter_for<_CharT>, _CharT> __fc,
44                                  basic_format_parse_context<_CharT> __pc) {
45                           { __f.parse(__pc) } -> same_as<typename basic_format_parse_context<_CharT>::iterator>;
46                           { __cf.format(__t, __fc) } -> same_as<__fmt_iter_for<_CharT>>;
47                         };
48 
49 #endif //_LIBCPP_STD_VER > 17
50 
51 _LIBCPP_END_NAMESPACE_STD
52 
53 #endif // _LIBCPP___FORMAT_CONCEPTS_H
54