/**
** {@inheritDoc}
**
** This will add {@code key} to both maps, even if one of the values
** of the tuple is {@code null}.
*/
@Override public X2<V0, V1> put(K key, X2<V0, V1> x) {
if (containsKey(key)) {
return Tuple.X2(m0.put(key, x._0), m1.put(key, x._1));
} else {
m0.put(key, x._0);
m1.put(key, x._1);
return null;
}
}
@Override public V put(U2<K0, K1> u, V val) {
return (u.type == 0)? m0.put(u.getT0(), val): m1.put(u.getT1(), val);
}