diff options
Diffstat (limited to 'contrib/llvm-project/libcxx/include/__ranges/drop_view.h')
-rw-r--r-- | contrib/llvm-project/libcxx/include/__ranges/drop_view.h | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/contrib/llvm-project/libcxx/include/__ranges/drop_view.h b/contrib/llvm-project/libcxx/include/__ranges/drop_view.h new file mode 100644 index 000000000000..099fd227111d --- /dev/null +++ b/contrib/llvm-project/libcxx/include/__ranges/drop_view.h @@ -0,0 +1,131 @@ +// -*- C++ -*- +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +#ifndef _LIBCPP___RANGES_DROP_VIEW_H +#define _LIBCPP___RANGES_DROP_VIEW_H + +#include <__config> +#include <__iterator/concepts.h> +#include <__iterator/iterator_traits.h> +#include <__iterator/next.h> +#include <__ranges/access.h> +#include <__ranges/all.h> +#include <__ranges/concepts.h> +#include <__ranges/enable_borrowed_range.h> +#include <__ranges/non_propagating_cache.h> +#include <__ranges/size.h> +#include <__ranges/view_interface.h> +#include <__utility/move.h> +#include <concepts> +#include <type_traits> + +#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) +#pragma GCC system_header +#endif + +_LIBCPP_PUSH_MACROS +#include <__undef_macros> + +_LIBCPP_BEGIN_NAMESPACE_STD + +#if !defined(_LIBCPP_HAS_NO_RANGES) + +namespace ranges { + template<view _View> + class drop_view + : public view_interface<drop_view<_View>> + { + // We cache begin() whenever ranges::next is not guaranteed O(1) to provide an + // amortized O(1) begin() method. If this is an input_range, then we cannot cache + // begin because begin is not equality preserving. + // Note: drop_view<input-range>::begin() is still trivially amortized O(1) because + // one can't call begin() on it more than once. + static constexpr bool _UseCache = forward_range<_View> && !(random_access_range<_View> && sized_range<_View>); + using _Cache = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>; + [[no_unique_address]] _Cache __cached_begin_ = _Cache(); + range_difference_t<_View> __count_ = 0; + _View __base_ = _View(); + +public: + drop_view() requires default_initializable<_View> = default; + + _LIBCPP_HIDE_FROM_ABI + constexpr drop_view(_View __base, range_difference_t<_View> __count) + : __count_(__count) + , __base_(_VSTD::move(__base)) + { + _LIBCPP_ASSERT(__count_ >= 0, "count must be greater than or equal to zero."); + } + + _LIBCPP_HIDE_FROM_ABI constexpr _View base() const& requires copy_constructible<_View> { return __base_; } + _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return _VSTD::move(__base_); } + + _LIBCPP_HIDE_FROM_ABI + constexpr auto begin() + requires (!(__simple_view<_View> && + random_access_range<const _View> && sized_range<const _View>)) + { + if constexpr (_UseCache) + if (__cached_begin_.__has_value()) + return *__cached_begin_; + + auto __tmp = ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_)); + if constexpr (_UseCache) + __cached_begin_.__set(__tmp); + return __tmp; + } + + _LIBCPP_HIDE_FROM_ABI + constexpr auto begin() const + requires random_access_range<const _View> && sized_range<const _View> + { + return ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_)); + } + + _LIBCPP_HIDE_FROM_ABI + constexpr auto end() + requires (!__simple_view<_View>) + { return ranges::end(__base_); } + + _LIBCPP_HIDE_FROM_ABI + constexpr auto end() const + requires range<const _View> + { return ranges::end(__base_); } + + _LIBCPP_HIDE_FROM_ABI + static constexpr auto __size(auto& __self) { + const auto __s = ranges::size(__self.__base_); + const auto __c = static_cast<decltype(__s)>(__self.__count_); + return __s < __c ? 0 : __s - __c; + } + + _LIBCPP_HIDE_FROM_ABI + constexpr auto size() + requires sized_range<_View> + { return __size(*this); } + + _LIBCPP_HIDE_FROM_ABI + constexpr auto size() const + requires sized_range<const _View> + { return __size(*this); } + }; + + template<class _Range> + drop_view(_Range&&, range_difference_t<_Range>) -> drop_view<views::all_t<_Range>>; + + template<class _Tp> + inline constexpr bool enable_borrowed_range<drop_view<_Tp>> = enable_borrowed_range<_Tp>; +} // namespace ranges + +#endif // !defined(_LIBCPP_HAS_NO_RANGES) + +_LIBCPP_END_NAMESPACE_STD + +_LIBCPP_POP_MACROS + +#endif // _LIBCPP___RANGES_DROP_VIEW_H |