ClickHouse/dbms/include/DB/Common/HashTable/ClearableHashMap.h

#pragma once

#include <DB/Common/HashTable/HashMap.h>
#include <DB/Common/HashTable/ClearableHashSet.h>


template <typename Key, typename Mapped, typename Hash>
struct ClearableHashMapCell : public ClearableHashTableCell<Key, HashMapCell<Key, Mapped, Hash, ClearableHashSetState>>
{
	using Base = ClearableHashTableCell<Key, HashMapCell<Key, Mapped, Hash, ClearableHashSetState>>;
	using Base::Base;

	ClearableHashMapCell(const typename Base::value_type & value_, const typename Base::State & state)
		: Base::BaseCell(value_, state), Base::version(state.version) {}
};


template
<
	typename Key,
	typename Mapped,
	typename Hash = DefaultHash<Key>,
	typename Grower = HashTableGrower<>,
	typename Allocator = HashTableAllocator
>
class ClearableHashMap : public HashTable<Key, ClearableHashMapCell<Key, Mapped, Hash>, Hash, Grower, Allocator>
{
public:
	using key_type = Key;
	using mapped_type = Mapped;
	using value_type = typename ClearableHashMap::cell_type::value_type;

	mapped_type & operator[](Key x)
	{
		typename ClearableHashMap::iterator it;
		bool inserted;
		this->emplace(x, it, inserted);

		if (inserted)
			new(&it->second) mapped_type();

		return it->second;
	}

	void clear()
	{
		++this->version;
		this->m_size = 0;
	}
};