[libcxx-commits] [libcxx] [libc++] Implement P2442R1 `std::views::chunk` (PR #171234)

[via libcxx-commits]

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+// -*- 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_CHUNK_VIEW_H
+#define _LIBCPP___RANGES_CHUNK_VIEW_H
+
+#include <__algorithm/ranges_min.h>
+#include <__assert>
+#include <__concepts/constructible.h>
+#include <__concepts/convertible_to.h>
+#include <__config>
+#include <__functional/bind_back.h>
+#include <__iterator/advance.h>
+#include <__iterator/concepts.h>
+#include <__iterator/default_sentinel.h>
+#include <__iterator/distance.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iter_swap.h>
+#include <__iterator/iterator_traits.h>
+#include <__memory/addressof.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/range_adaptor.h>
+#include <__ranges/take_view.h>
+#include <__ranges/view_interface.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/make_unsigned.h>
+#include <__utility/div_ceil.h>
+#include <__utility/forward.h>
+#include <__utility/move.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 <view _View>
+  requires input_range<_View>
+class chunk_view : public view_interface<chunk_view<_View>> {
+  _LIBCPP_NO_UNIQUE_ADDRESS _View __base_;
+  _LIBCPP_NO_UNIQUE_ADDRESS range_difference_t<_View> __n_;
+  _LIBCPP_NO_UNIQUE_ADDRESS range_difference_t<_View> __remainder_;
+  _LIBCPP_NO_UNIQUE_ADDRESS __non_propagating_cache<iterator_t<_View>> __current_;
+
+  class __outer_iterator;
+  class __inner_iterator;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit chunk_view(_View __base, range_difference_t<_View> __n)
+      : __base_(std::move(__base)), __n_(__n), __remainder_(0) {
+    _LIBCPP_ASSERT_PEDANTIC(__n > 0, "Trying to construct a chunk_view with chunk size <= 0");
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+    requires std::copy_constructible<_View>
+  {
+    return __base_;
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __outer_iterator begin() {
+    __current_.__emplace(ranges::begin(__base_));
+    __remainder_ = __n_;
+    return __outer_iterator(*this);
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr default_sentinel_t end() const noexcept {
+    return std::default_sentinel;
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+    requires sized_range<_View>
+  {
+    return std::__to_unsigned_like(__div_ceil(ranges::distance(__base_), __n_));
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+    requires sized_range<const _View>
+  {
+    return std::__to_unsigned_like(__div_ceil(ranges::distance(__base_), __n_));
+  }
+};
+
+template <view _View>
+  requires input_range<_View>
+class chunk_view<_View>::__outer_iterator {
+  friend chunk_view;
+
+  chunk_view* __parent_;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit __outer_iterator(chunk_view& __parent)
+      : __parent_(std::addressof(__parent)) {}
+
+public:
+  class value_type;
+  using iterator_concept = input_iterator_tag;
+  using difference_type  = range_difference_t<_View>;
+
+  _LIBCPP_HIDE_FROM_ABI __outer_iterator(__outer_iterator&&) = default;
+
+  _LIBCPP_HIDE_FROM_ABI __outer_iterator& operator=(__outer_iterator&&) = default;
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr value_type operator*() const {
+    _LIBCPP_ASSERT_PEDANTIC(*this != default_sentinel, "Trying to dereference past-the-end chunk_view iterator");
+    return value_type(*__parent_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __outer_iterator& operator++() {
+    _LIBCPP_ASSERT_PEDANTIC(*this != default_sentinel, "Trying to increment past-the-end chunk_view iterator");
+    ranges::advance(*__parent_->__current_, __parent_->__remainder_, ranges::end(__parent_->__base_));
+    __parent_->__remainder_ = __parent_->__n_;
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr void operator++(int) { ++*this; }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr bool
+  operator==(const __outer_iterator& __i, default_sentinel_t) {
+    return *__i.__parent_->__current_ == ranges::end(__i.__parent_->__base_) && __i.__parent_->__remainder_ != 0;
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type
+  operator-(default_sentinel_t, const __outer_iterator& __i)
+    requires sized_sentinel_for<sentinel_t<_View>, iterator_t<_View>>
+  {
+    const auto __dist = ranges::end(__i.__parent_->__base_) - *__i.__parent_->__current_;
+    if (__dist < __i.__parent_->__remainder_)
+      return __dist == 0 ? 0 : 1;
+    return __div_ceil(__dist - __i.__parent_->__remainder_, __i.__parent_->__n_) + 1;
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type
+  operator-(const __outer_iterator& __i, default_sentinel_t __s)
+    requires sized_sentinel_for<sentinel_t<_View>, iterator_t<_View>>
+  {
+    return -(__s - __i);
+  }
+};
+
+template <view _View>
+  requires input_range<_View>
+class chunk_view<_View>::__outer_iterator::value_type : public view_interface<value_type> {
----------------
huixie90 wrote:

I think the test for this class is missing

https://github.com/llvm/llvm-project/pull/171234