to see if the list works now.

上次面试的时候一个老外问的，我说在getStaffList（）中对于staffList做个
protected-copy，他没反应。
大家帮着想一想！谢谢啊！

pilbic class Company {
    private List staffList;

    public List void getStaffList() {
        return staffList;
    }

.....
}

public class EvilAgency() {

    public void buildContact() {

        List stafflist = myCompany.getStaffList();
        .....
        stafflist.clear(); //how to prevent this occuring?
    .....
    }
......
}

"""
Not Found
The requested URL /pipermail/python-chinese/ was not found on this server.
"""
呜乎哀哉！还有首页的快速退订入口怎么也没有了？？

2005/6/6, Jacob Fan <jacob at exoweb.net>:
> to see if the list works now.
> 
> _______________________________________________
> python-chinese list
> python-chinese at lists.python.cn
> http://python.cn/mailman/listinfo/python-chinese
> 


-- 
[Time is unimportant, only life important!]

List stafflist = myCompany.getStaffList();
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
应该是下面这样吧？？？
List stafflist = Company.getStaffList();

-----Original Message-----
From: python-chinese-bounces at lists.python.cn [mailto:python-chinese-bounces at lists.python.cn] On Behalf Of CaiJianFeng
Sent: Monday, June 06, 2005 3:57 PM
To: python-chinese at lists.python.cn
Subject: [python-chinese] How to prevent calling the clear method of thelist?

上次面试的时候一个老外问的，我说在getStaffList（）中对于staffList做个
protected-copy，他没反应。
大家帮着想一想！谢谢啊！

pilbic class Company {
    private List staffList;

    public List void getStaffList() {
        return staffList;
    }

.....
}

public class EvilAgency() {

    public void buildContact() {

        List stafflist = myCompany.getStaffList();
        .....
        stafflist.clear(); //how to prevent this occuring?
    .....
    }
......
}

_______________________________________________
python-chinese list
python-chinese at lists.python.cn
http://python.cn/mailman/listinfo/python-chinese

不好意思，说的不够清楚，myCompany是Company的一个实例，就代表某个公司吧。

EvilAgency在这里就是个保险机构，比如某个公司要为所有的员工上意外保险，就要和该公司每
个员工签署一份合同。

----- Original Message ----- 
From: "Neo Chan (netkiller)" <neo.chen at achievo.com>
To: <python-chinese at lists.python.cn>
Sent: Monday, June 06, 2005 4:54 PM
Subject: RE: [python-chinese] How to prevent calling the clear method
ofthelist?


> List stafflist = myCompany.getStaffList();
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 应该是下面这样吧？？？
> List stafflist = Company.getStaffList();
>
> -----Original Message-----
> From: python-chinese-bounces at lists.python.cn
[mailto:python-chinese-bounces at lists.python.cn] On Behalf Of CaiJianFeng
> Sent: Monday, June 06, 2005 3:57 PM
> To: python-chinese at lists.python.cn
> Subject: [python-chinese] How to prevent calling the clear method of
thelist?
>
> 上次面试的时候一个老外问的，我说在getStaffList（）中对于staffList做个
> protected-copy，他没反应。
> 大家帮着想一想！谢谢啊！
>
> pilbic class Company {
>     private List staffList;
>
>     public List void getStaffList() {
>         return staffList;
>     }
>
> .....
> }
>
> public class EvilAgency() {
>
>     public void buildContact() {
>
>         List stafflist = myCompany.getStaffList();
>         .....
>         stafflist.clear(); //how to prevent this occuring?
>     .....
>     }
> ......
> }
>
> _______________________________________________
> python-chinese list
> python-chinese at lists.python.cn
> http://python.cn/mailman/listinfo/python-chinese
>
> _______________________________________________
> python-chinese list
> python-chinese at lists.python.cn
> http://python.cn/mailman/listinfo/python-chinese

CaiJianFeng wrote:
> 上次面试的时候一个老外问的，我说在getStaffList（）中对于staffList做个
> protected-copy，他没反应。
> 大家帮着想一想！谢谢啊！
> 
> pilbic class Company {
>     private List staffList;
> 
>     public List void getStaffList() {
>         return staffList;
>     }
> 
> .....
> }
> 
> public class EvilAgency() {
> 
>     public void buildContact() {
> 
>         List stafflist = myCompany.getStaffList();
>         .....
>         stafflist.clear(); //how to prevent this occuring?
>     .....
>     }
> ......
> }
> 

做copy系统开销太大了，可以让getStaffList不直接返回staffList，而是返回一
个不具有clear方法的代理对象，可以考虑使用delegate pattern。

用python描述如下：

class ImmutableList(object):
    def __init__(self, obj):
        self.__obj = obj

    def __getattr__(self, attr):
        return getattr(self.__obj, attr)

    def clear(self):
        raise AttributeError

class Company(object):
    def getStaffList(self):
        return ImmutableList(self.__staffList)


-- 
Qiangning Hong

 ___________________________________________________________
/  No, I do not know what the Schadenfreude is. Please tell \
| me, because I'm dying to know.                            |
|                                                           |
| -- Homer Simpson                                          |
|                                                           |
\ When Flanders Failed                                      /
 -----------------------------------------------------------
    \
     \
      \
  ___       _____     ___
 /   \     /    /|   /   \
|     |   /    / |  |     |
|     |  /____/  |  |     |
|     |  |    |  |  |     |
|     |  | {} | /   |     |
|     |  |____|/    |     |
|     |    |==|     |     |
|      \___________/      |
|                         |
|                         |