Implement references using InvertibleRelation as data structure.

libdevcore/CMakeLists.txt

@@ -12,6 +12,7 @@ set(sources
 	FixedHash.h
 	IndentedWriter.cpp
 	IndentedWriter.h
+	InvertibleMap.h
 	IpfsHash.cpp
 	IpfsHash.h
 	JSON.cpp

libdevcore/InvertibleMap.h

@@ -0,0 +1,51 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include <map>
+#include <set>
+
+template <class T>
+struct InvertibleRelation
+{
+	/// forward[x] contains y <=> backward[y] contains x
+	std::map<T, std::set<T>> forward;
+	std::map<T, std::set<T>> backward;
+
+	void insert(T _key, T _value)
+	{
+		forward[_key].insert(_value);
+		backward[_value].insert(_key);
+	}
+
+	void set(T _key, std::set<T> _values)
+	{
+		for (T v: forward[_key])
+			backward[v].erase(_key);
+		for (T v: _values)
+			backward[v].insert(_key);
+		forward[_key] = std::move(_values);
+	}
+
+	void eraseKey(T _key)
+	{
+		for (auto const& v: forward[_key])
+			backward[v].erase(_key);
+		forward.erase(_key);
+	}
+};