private VectorExpression getCastWithFormat(
      GenericUDF udf, List<ExprNodeDesc> childExpr, TypeInfo returnType) throws HiveException {
    String inputType = childExpr.get(1).getTypeString();
    childExpr.remove(0); // index 0 not needed since we know returnType

    Class<?> veClass = getCastFormatVectorExpressionClass(childExpr, returnType, inputType);
    return createVectorExpression(
        veClass, childExpr, VectorExpressionDescriptor.Mode.PROJECTION, returnType, DataTypePhysicalVariation.NONE);
  }
Invoke special handling for expressions that can't be vectorized by regular
descriptor based lookup.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java