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

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,149 @@
+// -*- 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>
+
+#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.
+ */
+template <class _Container, class _Iterator>
+struct __ra_iterator {
+private:
+  _Iterator __iter_;
+
+  friend _Container;
+
+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()
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ldionne wrote:

We should probably make all of these operations `constexpr`.

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