Stephan Bergmann wrote:
> Mathias Bauer wrote:
>> Rainman Lee wrote:
>>
>>> hello everyone,
>>> I have a question about extending a published service.
>>> supposing that there is a published service S, which derives from a
>>> Multi-Inheritance Interface C, which inherits from A and B, like that:
>>> interface A
>>> {
>>> ...
>>> };
>>>
>>> interface B
>>> {
>>> ...
>>> };
>>>
>>> interface C
>>> {
>>> interface A;
>>> interface B;
>>> };
>>>
>>> service S : C;
>>>
>>> and the service S is published.
>>> now I want to make the service S suppot a new interface D, how can I
>>> archieve this while guaranteeing that old programs using service S
>>> still works?
>>> I know that the easiest way maybe implementing a service S1, and let
>>> this service supporting both the interface C and D.
>>> then new programs using interface D query S1, and the existing
>>> programs still query the service S.
>>> is there any other method to accomplish this? I want to new programs
>>> can access the interface D still through S instead of S1, S1 is not a
>>> friendly name I think ;@)
>>> thank you very much!
>>
>> If the implementation of service S1 also implements service S, all
>> clients using the service S will be able to use the additional interface
>> D by using queryInterface on the reference to interface C they got by
>> creating service S. Though I don't understand why new programs shouldn't
>> be able to use "S1".
>
> Querying an object that implements service S for interface D and using
> it as though the object implements service S1, though common practice,
> is not sound (in case the given object implements D with semantics
> different from those specified by S1).
Of course it's not sound in that regard (though IMHO will work in nearly
every case) but so is using service S in new code though service S1 is
already known. My suggestion is just the hacky solution for a hacky
requirement. :-)
Ciao,
Mathias
--
Mathias Bauer (mba) - Project Lead OpenOffice.org Writer
OpenOffice.org Engineering at Sun: http://blogs.sun.com/GullFOSS
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