d05ab119e1
The std::advance function has a clear precondition that it can only be called with a negative distance when a bidirectional iterator is used. However, prev() and next() don't have such preconditions explicitly, they inherit it from calling advance(). This patch removes assertions in prev() and next() that were duplicates of similar ones in advance(), and removes a copy-pasted comment that was trying to justify the use of _LIBCPP_ASSERT_PEDANTIC but IMO is creating confusion with little benefit.
85 lines
2.6 KiB
C++
85 lines
2.6 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 <__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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#include <__utility/move.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_PUSH_MACROS
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#include <__undef_macros>
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>
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[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter
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prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n) {
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std::advance(__x, -__n);
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return __x;
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}
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// LWG 3197
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// It is unclear what the implications of "BidirectionalIterator" in the standard are.
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// However, calling std::prev(non-bidi-iterator) is obviously an error and we should catch it at compile time.
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template <class _InputIter, __enable_if_t<__has_input_iterator_category<_InputIter>::value, int> = 0>
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _InputIter prev(_InputIter __it) {
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static_assert(__has_bidirectional_iterator_category<_InputIter>::value,
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"Attempt to prev(it) with a non-bidirectional iterator");
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return std::prev(std::move(__it), 1);
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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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struct __prev {
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template <bidirectional_iterator _Ip>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI 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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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip
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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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inline namespace __cpo {
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inline constexpr auto prev = __prev{};
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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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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___ITERATOR_PREV_H
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