@Override
    public int hashCode() {
        int result = super.hashCode();
        result = 31 * result + dateToken.hashCode();
        result = 31 * result + duration.hashCode();
        result = 31 * result + value;
        return result;
    }
Reference implementation for date concatenation step.

@author Valentyn Kahamlyk
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/DateAddStep.java