怎么才能让自定义属性对用户只读

clea
otest=CREATEOBJECT('employee')
otest.hiredate={^2022-12-01}
?otest.hiredate
otest.sethiredate()
?otest.hiredate

DEFINE CLASS employee AS CUSTOM
    *!*    HIDDEN HireDate
    *!*    PROTECTED HireDate
    First_Name = "Jiang"
    Last_Name = "Sam"
    Address = ""
    HireDate = {^2017-06-05}
    cprogramname=[] &&用来判断修改者

PROCEDURE GetHireDate
  RETURN This.HireDate
ENDPROC

PROCEDURE hiredate_assign
PARAMETERS m.vnewval
m.voldval=this.hiredate

if strextract(this.cprogramname,[.],[])==UPPER([sethiredate])
*!*    检查cprogramname修改者是不是我们制定的方法   
    this.hiredate=m.vnewval
ELSE
    this.hiredate=m.voldval
ENDIF
this.cprogramname=[] &&恢复不可修改状态
   
PROCEDURE sethiredate
    this.cprogramname=PROGRAM() &&传递方法名给属性cprogramname
    this.hiredate=DATE()
ENDDEFINE