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

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,59 @@
+// -*- 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
+#define _LIBCPP_FLAT_SET
+
+/*
+  Header <flat_set> synopsis
+
+#include <compare>              // see [compare.syn]
+#include <initializer_list>     // see [initializer.list.syn]
+
+namespace std {
+  // [flat.set], class template flat_set
+  template<class Key, class Compare = less<Key>, class KeyContainer = vector<Key>>
+    class flat_set;
+
+  struct sorted_unique_t { explicit sorted_unique_t() = default; };
+  inline constexpr sorted_unique_t sorted_unique{};
+
+  template<class Key, class Compare, class KeyContainer, class Allocator>
+    struct uses_allocator<flat_set<Key, Compare, KeyContainer>, Allocator>;
+
+  // [flat.set.erasure], erasure for flat_set
+  template<class Key, class Compare, class KeyContainer, class Predicate>
+    typename flat_set<Key, Compare, KeyContainer>::size_type
+      erase_if(flat_set<Key, Compare, KeyContainer>& c, Predicate pred);
+}
+*/
+
+#if __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
+#  include <__cxx03/__config>
+#else
+#  include <__config>
+
+#  if _LIBCPP_STD_VER >= 23
+#    include <__flat_map/sorted_unique.h>
+#    include <__flat_set/flat_set.h>
+#  endif
+
+// for feature-test macros
+#  include <version>
+
+// standard required includes
----------------
frederick-vs-ja wrote:

How about implementing [LWG3987](https://cplusplus.github.io/LWG/issue3987) (#105309)? Is it already implemented by the complicated transitive inclusions?

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