hash method

int hash (E e)

override

Get a hashcode of an element.

The hashcode should be compatible with equals, so that if equals(a, b) then hash(a) == hash(b).

Implementation

int hash(E e) {
  for (Equality<E> eq in _equalities) {
    if (eq.isValidKey(e)) return eq.hash(e);
  }
  return 0;
}