protected Collection<VectorExpression> getChildExpressionsForTransientInit() {
    Collection<VectorExpression> result = new ArrayList<>(super.getChildExpressionsForTransientInit());
    Collections.addAll(result, structExpressions);
    return result;
  }
After construction you must call setInListValues() to add the values to the IN set
(on the IStringInExpr interface).
<p>
And, call a and b on the IStructInExpr interface.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/FilterStructColumnInList.java