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| 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 _LIBCPP_NODEBUG = _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 >= 17 |
| 47 | |
| 48 | template <class... _Args> |
| 49 | struct _LIBCPP_NO_SPECIALIZATIONS disjunction : _Or<_Args...> {}; |
| 50 | |
| 51 | template <class... _Args> |
| 52 | _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool disjunction_v = _Or<_Args...>::value; |
| 53 | |
| 54 | #endif // _LIBCPP_STD_VER >= 17 |
| 55 | |
| 56 | _LIBCPP_END_NAMESPACE_STD |
| 57 | |
| 58 | #endif // _LIBCPP___TYPE_TRAITS_DISJUNCTION_H |
| 59 |
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