@Override
        public int hashCode() {
            int result = super.hashCode();
            if (null != this.matchKey)
                result ^= this.matchKey.hashCode();
            return result;
        }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MatchStep.java