@Override
      public Object setValue(Object field, byte[] value, int start, int length) 
          throws HiveException {
        if (null == field) {
          field = initValue(null);
        }
        text.set(value, start, length);
        ((SettableHiveCharObjectInspector) this.objectInspector).set(field, text.toString());
        return field;
      }
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