@Override
    public void configure(final Object... keyValues) {
        final int indexer;
        if (keyValues[0].equals(WithOptions.indexer)) {
            if (keyValues.length == 2 && keyValues[1] instanceof Integer) {
                indexer = (Integer) keyValues[1];
            } else {
                throw INVALID_CONFIGURATION_EXCEPTION;
            }
            if (indexer == WithOptions.list) {
                this.indexerType = IndexerType.LIST;
                this.indexer = ListIndexFunction.instance();
            } else if (indexer == WithOptions.map) {
                this.indexerType = IndexerType.MAP;
                this.indexer = MapIndexFunction.instance();
            } else {
                throw INVALID_CONFIGURATION_EXCEPTION;
            }
        } else {
            this.parameters.set(this, keyValues);
        }
    }
Gets the type of indexer that is configured for this step.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/IndexStep.java