[libcxx-commits] [libcxx] [libc++] implement std::flat_set (PR #125241)

[A. Jiang via libcxx-commits]

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@@ -0,0 +1,155 @@
+// -*- 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___FLAT_SET_RA_ITERATOR_H
+#define _LIBCPP___FLAT_SET_RA_ITERATOR_H
+
+#include <__compare/three_way_comparable.h>
+#include <__config>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/is_constructible.h>
+#include <__utility/move.h>
+#include <iterator>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if _LIBCPP_STD_VER >= 23
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+/**
+ * __ra_iterator is a random access iterator that wraps an underlying iterator.
+ * It also stores the underlying container type in its type so that algorithms
+ * can optimize based on the underlying container type, and to avoid inadvertently
+ * mixing iterators coming from different containers..
+ */
+template <class _Container, class _Iterator>
+struct __ra_iterator {
+private:
+  _Iterator __iter_;
+
+  friend _Container;
+
+  static_assert(std::random_access_iterator<_Iterator>, "Underlying iterator must be a random access iterator");
+
+public:
+  using iterator_concept  = random_access_iterator_tag; // deliberately lower contiguous_iterator
+  using iterator_category = random_access_iterator_tag;
+  using value_type        = iter_value_t<_Iterator>;
+  using difference_type   = iter_difference_t<_Iterator>;
+
+  _LIBCPP_HIDE_FROM_ABI __ra_iterator()
+    requires is_default_constructible_v<_Iterator>
+  = default;
+
+  _LIBCPP_HIDE_FROM_ABI explicit constexpr __ra_iterator(_Iterator __iter) : __iter_(std::move(__iter)) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iterator __base() const noexcept(noexcept(_Iterator(__iter_))) { return __iter_; }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const { return *__iter_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator->() const
+    requires requires { __iter_.operator->(); }
+  {
+    return __iter_.operator->();
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator++() {
+    ++__iter_;
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator operator++(int) {
+    __ra_iterator __tmp(*this);
+    ++*this;
+    return __tmp;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator--() {
+    --__iter_;
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator operator--(int) {
+    __ra_iterator __tmp(*this);
+    --*this;
+    return __tmp;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator+=(difference_type __x) {
+    __iter_ += __x;
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __ra_iterator& operator-=(difference_type __x) {
+    __iter_ -= __x;
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](difference_type __n) const { return *(*this + __n); }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const __ra_iterator& __x, const __ra_iterator& __y) {
+    return __x.__iter_ == __y.__iter_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<(const __ra_iterator& __x, const __ra_iterator& __y) {
+    return __x.__iter_ < __y.__iter_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>(const __ra_iterator& __x, const __ra_iterator& __y) {
+    return __y < __x;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<=(const __ra_iterator& __x, const __ra_iterator& __y) {
+    return !(__y < __x);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>=(const __ra_iterator& __x, const __ra_iterator& __y) {
+    return !(__x < __y);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(const __ra_iterator& __x, const __ra_iterator& __y)
+    requires three_way_comparable<_Iterator>
+  {
+    return __x.__iter_ <=> __y.__iter_;
+  }
----------------
frederick-vs-ja wrote:

IIUC the `requires` here is unnecessary. As specified in [[container.reqmts]/39](https://eel.is/c++draft/container.reqmts#39), [/40](https://eel.is/c++draft/container.reqmts#40), and [/41](https://eel.is/c++draft/container.reqmts#41), use of non-three-way-comparable iterator here is invalid, and the return type is required to be `std::strong_ordering`.

https://github.com/llvm/llvm-project/pull/125241