[libcxx-commits] [libcxx] WIP: [libc++][ranges] Implement `ranges::slide_view` (PR #67146)

[Xiaoyang Liu via libcxx-commits]

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@@ -0,0 +1,315 @@
+// -*- 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_SLIDE_VIEW_H
+#define _LIBCPP___RANGES_SLIDE_VIEW_H
+
+#include <__assert>
+#include <__concepts/constructible.h>
+#include <__concepts/convertible_to.h>
+#include <__config>
+#include <__functional/bind_back.h>
+#include <__iterator/concepts.h>
+#include <__iterator/default_sentinel.h>
+#include <__iterator/distance.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
+#include <__iterator/prev.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/counted.h>
+#include <__ranges/empty_view.h>
+#include <__ranges/non_propagating_cache.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/view_interface.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+
+template <typename _V>
+concept __slide_caches_nothing = random_access_range<_V> && sized_range<_V>;
+template <typename _V>
+concept __slide_caches_last = !__slide_caches_nothing<_V> && bidirectional_range<_V> && common_range<_V>;
+template <typename _V>
+concept __slide_caches_first = !__slide_caches_nothing<_V> && !__slide_caches_last<_V>;
+
+template <forward_range _View>
+  requires view<_View>
+class slide_view : public view_interface<slide_view<_View>> {
+public:
+  template <bool>
+  class __iterator;
+  class __sentinel;
+
+private:
+  _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
+  range_difference_t<_View> __n_          = 0;
+  using _Cache = _If<!(__slide_caches_nothing<_View>), __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
+  _Cache __cached_begin_;
+  _Cache __cached_end_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit slide_view(_View __base, range_difference_t<_View> __n)
+      : __base_(std::move(__base)), __n_(__n) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+    requires copy_constructible<_View>
+  {
+    return __base_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+    requires(!(__simple_view<_View> && __slide_caches_nothing<const _View>) && __slide_caches_last<_View>)
+  {
+    auto __first = ranges::begin(__base_);
+    if (!__cached_begin_.__has_value()) {
+      __cached_begin_.__emplace(ranges::next(__first, __n_ - 1, ranges::end(__base_)));
+    }
+    return __iterator<false>(__first, __cached_begin_, __n_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+    requires(!(__simple_view<_View> && __slide_caches_nothing<const _View>))
+  {
+    return __iterator<false>(ranges::begin(__base_), __n_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+    requires __slide_caches_nothing<_View>
+  {
+    return __iterator<true>(ranges::begin(__base_), __n_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+    requires(!(__simple_view<_View> && __slide_caches_nothing<const _View>))
+  {
+    if constexpr (__slide_caches_nothing<_View>) {
+      return __iterator<false>(ranges::begin(__base_) + range_difference_t<_View>(size()), __n_);
+    } else if constexpr (__slide_caches_last<_View>) {
+      return __iterator<false>(ranges::prev(ranges::end(__base_), __n_ - 1, ranges::begin(__base_)), __n_);
+    } else if constexpr (common_range<_View>) {
+      return __iterator<false>(ranges::end(__base_), ranges::end(__base_), __n_);
+    } else {
+      return sentinel<false>(ranges::end(__base_));
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+    requires __slide_caches_nothing<const _View>
+  {
+    return begin() + range_difference_t<const _View>(size());
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+    requires sized_range<const _View>
+  {
+    auto __size = ranges::distance(__base_) - __n_ + 1;
+    if (__size < 0) {
+      __size = 0;
+    }
+    return std::__to_unsigned_like(__size);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+    requires sized_range<_View>
+  {
+    auto __size = ranges::distance(__base_) - __n_ + 1;
+    if (__size < 0) {
+      __size = 0;
+    }
+    return __size;
+  }
+};
+
+template <class _Range>
+slide_view(_Range&&) -> slide_view<views::all_t<_Range>>;
+
+template <class _View>
+struct __slide_view_iterator_concept {
+  using type = forward_iterator_tag;
+};
+
+template <random_access_range _View>
+struct __slide_view_iterator_concept<_View> {
+  using type = random_access_iterator_tag;
+};
+
+template <bidirectional_range _View>
+struct __slide_view_iterator_concept<_View> {
+  using type = bidirectional_iterator_tag;
+};
+
+template <forward_range _View>
+  requires view<_View>
+template <bool _Const>
+class slide_view<_View>::__iterator : public __slide_view_iterator_concept<_View> {
+  friend slide_view;
+
+  using _Base           = __maybe_const<_Const, _View>;
+  using _Last           = _If<__slide_caches_first<_Base>, iterator_t<_Base>, empty_view<_Base>>;
+  slide_view* __parent_ = nullptr;
+  _LIBCPP_NO_UNIQUE_ADDRESS iterator_t<_Base> __current_ = iterator_t<_Base>();
+  _LIBCPP_NO_UNIQUE_ADDRESS _Last __last_                = {};
+  range_difference_t<_Base> __n_                         = 0;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator(iterator_t<_Base> __current, range_difference_t<_Base> __n)
+    requires(!(__slide_caches_first<_Base>))
+      : __current_(__current), __n_(__n) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator(iterator_t<_Base> __current, _Last __last, range_difference_t<_Base> __n)
+    requires(__slide_caches_first<_Base>)
+      : __current_(__current), __last_(__last), __n_(__n) {}
+
+public:
+  using value_type        = decltype(views::counted(__current_, __n_));
+  using difference_type   = range_difference_t<_Base>;
+  using iterator_category = input_iterator_tag;
+  using iterator_concept  = __slide_view_iterator_concept<_Base>;
+
+  _LIBCPP_HIDE_FROM_ABI __iterator() = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator(__iterator<!_Const> __i)
+    requires _Const && convertible_to<iterator_t<_View>, iterator_t<_Base>>
+      : __current_(std::move(__i.__current_)), __n_(__i.__n_) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto operator*() const { return views::counted(__current_, __n_); }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator++() {
+    __current_ = ranges::next(__current_);
+    if constexpr (__slide_caches_first<_Base>) {
+      __last_ = ranges::next(__last_);
+    }
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator operator++(int) {
+    auto __tmp = *this;
+    ++*this;
+    return __tmp;
+    // TODO ...
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator--()
+    requires bidirectional_range<_View>
+  {
+    __current_ = ranges::prev(__current_);
+    if constexpr (__slide_caches_first<_Base>) {
+      __last_ = std::prev(__last_);
+    }
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator operator--(int)
+    requires bidirectional_range<_View>
+  {
+    auto __tmp = *this;
+    --*this;
+    return __tmp;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator-=(difference_type __x)
+    requires random_access_range<_Base>
+  {
+    __current_ = std::prev(__current_, __x);
+    if constexpr (__slide_caches_first<_Base>) {
+      __last_ = std::prev(__last_, __x);
+    }
+    return *this;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator operator+=(difference_type __x)
+    requires random_access_range<_Base>
+  {
+    __current_ = std::next(__current_, __x);
+    if constexpr (__slide_caches_first<_Base>) {
+      __last_ = std::next(__last_, __x);
+    }
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto operator[](difference_type __x) const
+    requires random_access_range<_Base>
+  {
+    return views::counted(__current_ + __x, __n_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const __iterator& __x, const __iterator& __y) {
+    if constexpr (__slide_caches_first<_Base>) {
+      __x.__last_ == __y.__last_;
----------------
xiaoyang-sde wrote:

```suggestion
      return __x.__last_ == __y.__last_;
```

https://github.com/llvm/llvm-project/pull/67146