// Although we implement IReadOnlyDictionary, note that the Values class is mutable!
bool IReadOnlyDictionary <K, ValueList> .TryGetValue(K key, out BMultiMap <K, V> .ValueList value)
{
value = this[key]; // always succeeds
return(true); // not sure if always returning true is a good idea, but it's fast
}
internal ValueList(BMultiMap <K, V> map, K key)
{
_map = map;
_key = key;
}