85 lines
2.2 KiB
C++
85 lines
2.2 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___RANGES_EMPTY_H
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#define _LIBCPP___RANGES_EMPTY_H
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#include <__config>
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#include <__iterator/concepts.h>
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#include <__ranges/size.h>
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#include <type_traits>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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#pragma GCC system_header
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#endif
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_LIBCPP_PUSH_MACROS
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#include <__undef_macros>
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if !defined(_LIBCPP_HAS_NO_RANGES)
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// clang-format off
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namespace ranges {
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// [range.prim.empty]
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namespace __empty {
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template <class _Tp>
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concept __member_empty = requires(_Tp&& __t) {
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bool(_VSTD::forward<_Tp>(__t).empty());
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};
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template<class _Tp>
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concept __can_invoke_size =
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!__member_empty<_Tp> &&
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requires(_Tp&& __t) { ranges::size(_VSTD::forward<_Tp>(__t)); };
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template <class _Tp>
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concept __can_compare_begin_end =
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!__member_empty<_Tp> &&
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!__can_invoke_size<_Tp> &&
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requires(_Tp&& __t) {
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bool(ranges::begin(__t) == ranges::end(__t));
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{ ranges::begin(__t) } -> forward_iterator;
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};
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struct __fn {
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template <__member_empty _Tp>
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[[nodiscard]] constexpr bool operator()(_Tp&& __t) const
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noexcept(noexcept(bool(__t.empty()))) {
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return __t.empty();
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}
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template <__can_invoke_size _Tp>
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[[nodiscard]] constexpr bool operator()(_Tp&& __t) const
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noexcept(noexcept(ranges::size(_VSTD::forward<_Tp>(__t)))) {
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return ranges::size(_VSTD::forward<_Tp>(__t)) == 0;
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}
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template<__can_compare_begin_end _Tp>
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[[nodiscard]] constexpr bool operator()(_Tp&& __t) const
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noexcept(noexcept(bool(ranges::begin(__t) == ranges::end(__t)))) {
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return ranges::begin(__t) == ranges::end(__t);
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}
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};
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}
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inline namespace __cpo {
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inline constexpr auto empty = __empty::__fn{};
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} // namespace __cpo
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} // namespace ranges
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// clang-format off
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#endif // !defined(_LIBCPP_HAS_NO_RANGES)
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_LIBCPP_END_NAMESPACE_STD
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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___RANGES_EMPTY_H
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