| // -*- 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/size.h> |
| #include <__ranges/view_interface.h> |
| #include <optional> |
| #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 = optional<iterator_t<_View>>; |
| struct _Empty { }; |
| |
| // For forward ranges use std::optional to cache the begin iterator. |
| // No unique address + _Empty means we don't use any extra space when this |
| // is not a forward iterator. |
| [[no_unique_address]] conditional_t<_UseCache, _Cache, _Empty> __cached_begin_; |
| 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) |
| : __cached_begin_() |
| , __count_(__count) |
| , __base_(_VSTD::move(__base)) |
| { |
| _LIBCPP_ASSERT(__count_ >= 0, "count must be greater than or equal to zero."); |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr drop_view(drop_view const& __other) |
| : __cached_begin_() // Intentionally not propagating the cached begin iterator. |
| , __count_(__other.__count_) |
| , __base_(__other.__base_) |
| { } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr drop_view(drop_view&& __other) |
| : __cached_begin_() // Intentionally not propagating the cached begin iterator. |
| , __count_(_VSTD::move(__other.__count_)) |
| , __base_(_VSTD::move(__other.__base_)) |
| { } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr drop_view& operator=(drop_view const& __other) { |
| if constexpr (_UseCache) { |
| __cached_begin_.reset(); |
| } |
| __base_ = __other.__base_; |
| __count_ = __other.__count_; |
| return *this; |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| constexpr drop_view& operator=(drop_view&& __other) { |
| if constexpr (_UseCache) { |
| __cached_begin_.reset(); |
| __other.__cached_begin_.reset(); |
| } |
| __base_ = _VSTD::move(__other.__base_); |
| __count_ = _VSTD::move(__other.__count_); |
| return *this; |
| } |
| |
| _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_) |
| return *__cached_begin_; |
| |
| auto __tmp = ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_)); |
| if constexpr (_UseCache) |
| __cached_begin_ = __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 |