Bottom line - is I understand correctly this isn't an interface question
- is more a question concerning a particular implemetation approach at
the container/SM/CM level?
Steve.
Peter Donald wrote:
> Hi,
>
> After playing with the meta-info and going through a few use-cases one
> of the questions that is still not answered. The main one is whether
> it is valid for their to be "optional" entries in the ServiceManager
> and/or Context. For instance would the following be valid use case in
> case of ServiceManager
>
> void service( ServiceManager sm ) throws ServiceException
> {
> if( sm.hasService( MyOptionalService.ROLE )
> {
> myOptionalService = (MyOptionalService)sm.lookup(
> MyOptionalService.ROLE );
> }
> }
>
> Ages ago we decided that it was bad form to do the above, however I
> believe Berin has changed his mind (?) and I never really minded it.
> For those of you who weren't around the main reason we decided we did
> not like it was because it allowed the possibility of the following
> kind of code
>
> if( sm.hasService( MyService.ROLE + "/key3" ) ) { ...use that
> service... }
> else if( sm.hasService( MyService.ROLE + "/key2" ) ) { ...use that
> service... }
> else if( sm.hasService( MyService.ROLE + "/key1" ) ) { ...use that
> service... }
> else { ...use the base service... }
>
> The above code is bad as it mixes concerns. It should be
> responsibility of assembler to map correct service implementation onto
> single key rather than the developer who dictates assembly structure.
>
> In most cases "optional" entrys will never be used but in some (rare)
> cases it could be useful. For example in Phoenix we have one case
> where optional would be useful. What we end up having to do is create
> a NoopSystemManager. There is a few cases in myrmidon that I would
> also benefit from allowing "optional" entrys in context/serviceManager.
>
> Any problems with relaxing and allowing optional thingies?
>
>
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Stephen J. McConnell
OSM SARL
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