public VectorExpressionWriter init(SettableHiveVarcharObjectInspector objInspector)
          throws HiveException {
        super.init(objInspector);
        this.text = new Text();
        this.obj = initValue(null);
        return this;
      }
Compiles the appropriate vector expression writers based on a struct object
inspector.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/VectorExpressionWriterFactory.java