Knowledge about storage.

libdevcore/InvertibleMap.h

@@ -20,6 +20,48 @@
 #include <map>
 #include <set>
 
+/**
+ * Data structure that keeps track of values and keys of a mapping.
+ */
+template <class K, class V>
+struct InvertibleMap
+{
+	std::map<K, V> values;
+	// references[x] == {y | values[y] == x}
+	std::map<V, std::set<K>> references;
+
+	void set(K _key, V _value)
+	{
+		if (values.count(_key))
+			references[values[_key]].erase(_key);
+		values[_key] = _value;
+		references[_value].insert(_key);
+	}
+
+	void eraseKey(K _key)
+	{
+		if (values.count(_key))
+			references[values[_key]].erase(_key);
+		values.erase(_key);
+	}
+
+	void eraseValue(V _value)
+	{
+		if (references.count(_value))
+		{
+			for (V v: references[_value])
+				values.erase(v);
+			references.erase(_value);
+		}
+	}
+
+	void clear()
+	{
+		values.clear();
+		references.clear();
+	}
+};
+
 template <class T>
 struct InvertibleRelation
 {