code: func (cwc *ColWithCmpFuncManager) String() string {
  	buffer := bytes.NewBufferString("")
  	for i := range cwc.OpType {
  		buffer.WriteString(fmt.Sprintf("%v(%v, %v)", cwc.OpType[i], cwc.targetCol, cwc.opArg[i]))
  		if i < len(cwc.OpType)-1 {
  			buffer.WriteString(" ")
  		}
  	}
  	return buffer.String()
  }
docs: // String implements Stringer interface.