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