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// -*- C++ -*-
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include <__config>
#include <__debug>
#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>
#pragma GCC system_header
#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();
drop_view() requires default_initializable<_View> = default;
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_); }
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)
return __tmp;
constexpr auto begin() const
requires random_access_range<const _View> && sized_range<const _View>
return ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
constexpr auto end()
requires (!__simple_view<_View>)
{ return ranges::end(__base_); }
constexpr auto end() const
requires range<const _View>
{ return ranges::end(__base_); }
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;
constexpr auto size()
requires sized_range<_View>
{ return __size(*this); }
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)