Get a hash code for this object.
All objects have hash codes. Hash codes are guaranteed to be the
same for objects that are equal when compared using the equality
operator ==. Other than that there are no guarantees about
the hash codes. They will not be consistent between runs and
there are no distribution guarantees.
If a subclass overrides hashCode it should override the
equality operator as well to maintain consistency.
Source
int get hashCode => _JenkinsSmiHash.hash4(left.hashCode, top.hashCode,
right.hashCode, bottom.hashCode);