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_DISJUNCTION_H
10 #define _LIBCPP___TYPE_TRAITS_DISJUNCTION_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 template <bool>
22 struct _OrImpl;
23 
24 template <>
25 struct _OrImpl<true> {
26   template <class _Res, class _First, class... _Rest>
27   using _Result _LIBCPP_NODEBUG =
28       typename _OrImpl<!bool(_First::value) && sizeof...(_Rest) != 0>::template _Result<_First, _Rest...>;
29 };
30 
31 template <>
32 struct _OrImpl<false> {
33   template <class _Res, class...>
34   using _Result = _Res;
35 };
36 
37 // _Or always performs lazy evaluation of its arguments.
38 //
39 // However, `_Or<_Pred...>` itself will evaluate its result immediately (without having to
40 // be instantiated) since it is an alias, unlike `disjunction<_Pred...>`, which is a struct.
41 // If you want to defer the evaluation of `_Or<_Pred...>` itself, use `_Lazy<_Or, _Pred...>`
42 // or `disjunction<_Pred...>` directly.
43 template <class... _Args>
44 using _Or _LIBCPP_NODEBUG = typename _OrImpl<sizeof...(_Args) != 0>::template _Result<false_type, _Args...>;
45 
46 #if _LIBCPP_STD_VER > 14
47 
48 template <class... _Args>
49 struct disjunction : _Or<_Args...> {};
50 
51 template <class... _Args>
52 inline constexpr bool disjunction_v = _Or<_Args...>::value;
53 
54 #endif // _LIBCPP_STD_VER > 14
55 
56 _LIBCPP_END_NAMESPACE_STD
57 
58 #endif // _LIBCPP___TYPE_TRAITS_DISJUNCTION_H
59