Add simple initial draft of unordered_flat_map

include/boost/unordered/unordered_flat_map.hpp

@@ -0,0 +1,90 @@
+#ifndef BOOST_UNORDERED_UNORDERED_FLAT_MAP_HPP_INCLUDED
+#define BOOST_UNORDERED_UNORDERED_FLAT_MAP_HPP_INCLUDED
+
+#include <boost/config.hpp>
+#if defined(BOOST_HAS_PRAGMA_ONCE)
+#pragma once
+#endif
+
+#include <boost/unordered/detail/foa.hpp>
+
+#include <boost/core/allocator_access.hpp>
+
+#include <utility>
+
+namespace boost {
+  namespace unordered {
+    template <class Key, class T, class Hash, class KeyEqual, class Allocator>
+    class unordered_flat_map
+    {
+      struct map_types
+      {
+        using key_type = Key;
+        using value_type = std::pair<Key const, T>;
+        static Key const& extract(value_type const& kv) { return kv.first; }
+      };
+
+      using table_type = detail::foa::table<map_types, Hash, KeyEqual,
+        typename boost::allocator_rebind<Allocator,
+          typename map_types::value_type>::type>;
+
+      table_type table_;
+
+    public:
+      using key_type = Key;
+      using mapped_type = T;
+      using value_type = typename map_types::value_type;
+      using size_type = std::size_t;
+      using key_equal = KeyEqual;
+      using iterator = typename table_type::iterator;
+      using const_iterator = typename table_type::const_iterator;
+
+      iterator begin() noexcept { return table_.begin(); }
+      const_iterator begin() const noexcept { return table_.begin(); }
+      const_iterator cbegin() const noexcept { return table_.cbegin(); }
+
+      iterator end() noexcept { return table_.end(); }
+      const_iterator end() const noexcept { return table_.end(); }
+      const_iterator cend() const noexcept { return table_.cend(); }
+
+      size_type size() const noexcept { return table_.size(); }
+
+      std::pair<iterator, bool> insert(value_type const& value)
+      {
+        return table_.insert(value);
+      }
+
+      size_type count(key_type const& key) const
+      {
+        auto pos = table_.find(key);
+        return pos != table_.end() ? 1 : 0;
+      }
+
+      std::pair<iterator, iterator> equal_range(key_type const& key)
+      {
+        auto pos = table_.find(key);
+        return {pos, pos == table_.end() ? pos : ++pos};
+      }
+
+      std::pair<const_iterator, const_iterator> equal_range(
+        key_type const& key) const
+      {
+        auto pos = table_.find(key);
+        return {pos, pos == table_.end() ? pos : ++pos};
+      }
+
+      size_type bucket_count() const noexcept { return table_.capacity(); }
+
+      float load_factor() const noexcept { return table_.load_factor(); }
+
+      float max_load_factor() const noexcept
+      {
+        return table_.max_load_factor();
+      }
+
+      key_equal key_eq() const { return table_.key_eq(); }
+    };
+  } // namespace unordered
+} // namespace boost
+
+#endif