80643d9366
We plan to add concepts for checking that iterators actually provide what they claim to. This is to avoid people thinking that these type traits actually check the iterator requirements in more detail. Reviewed By: ldionne, #libc Spies: Mordante, libcxx-commits, wenlei Differential Revision: https://reviews.llvm.org/D150801
78 lines
2.1 KiB
C++
78 lines
2.1 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___ITERATOR_PREV_H
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#define _LIBCPP___ITERATOR_PREV_H
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#include <__assert>
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#include <__config>
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#include <__iterator/advance.h>
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#include <__iterator/concepts.h>
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#include <__iterator/incrementable_traits.h>
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#include <__iterator/iterator_traits.h>
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#include <__type_traits/enable_if.h>
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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_BEGIN_NAMESPACE_STD
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template <class _InputIter>
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inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX17
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typename enable_if<__has_input_iterator_category<_InputIter>::value, _InputIter>::type
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prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n = 1) {
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_LIBCPP_ASSERT(__n <= 0 || __has_bidirectional_iterator_category<_InputIter>::value,
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"Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
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_VSTD::advance(__x, -__n);
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return __x;
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}
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#if _LIBCPP_STD_VER >= 20
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// [range.iter.op.prev]
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namespace ranges {
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namespace __prev {
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struct __fn {
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template <bidirectional_iterator _Ip>
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_LIBCPP_HIDE_FROM_ABI
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constexpr _Ip operator()(_Ip __x) const {
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--__x;
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return __x;
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}
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template <bidirectional_iterator _Ip>
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_LIBCPP_HIDE_FROM_ABI
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constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
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ranges::advance(__x, -__n);
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return __x;
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}
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template <bidirectional_iterator _Ip>
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_LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
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ranges::advance(__x, -__n, __bound_iter);
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return __x;
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}
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};
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} // namespace __prev
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inline namespace __cpo {
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inline constexpr auto prev = __prev::__fn{};
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} // namespace __cpo
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} // namespace ranges
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#endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ITERATOR_PREV_H
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