Re: [e4-dev] Having multiple IContextFunction

[Oleg Besedin <obesedin@xxxxxxxxxx>]

Hi Tom,
This is the expected behavior. Having
multiple services can be a valid scenario. For example, imagine that we
ship e4 SDK with a "generic" implementation of a, say, weather
service. A developer downloads the SDK and says, "hey, this weather
service... hmm... does not provide long-term forecasts within expected
tolerances". With multiple services allowed, in theory, the developer
then can make his own weather service and register it with OSGi with a
higher ranking.

(Unfortunately iterating services to
find the "best" answer won't work as at the dependency injector
level we don't know what "best" means; "null" can be
a valid answer too.)

This is simplicity vs. extensibility
in action :-). I am not claiming that we have found the best balance, so
if the reasons above don't sound convincing please open a bug/enhancement
request and we'll follow up there.

Sincerely,
Oleg Besedin

From:	Tom Schindl <tom.schindl@xxxxxxxxxxxxxxx>
To:	E4 Project developer mailing list <e4-dev@xxxxxxxxxxx>
Date:	05/20/2010 09:31 AM
Subject:	[e4-dev] Having multiple IContextFunction
Sent by:	e4-dev-bounces@xxxxxxxxxxx

---

Hi,

Today i came across a problem that I had 2 DS-Services defining the same
"service.context.key" because both functions are able to contruct
the
same Service-Interface in different contexts.

When I launched my inner 4.0 Workbench my model-editor didn't came up
because it said that there was a missing DI-Argument.

The reason was that DI consulted only one of the contributed functions
which was not able to construct a service in the given context and so
refused to create my Component-POJO.

Is this behaviour expected and if it is it would it probably make sense
to log a warning if 2 IContextFunctions define the same service.context.key.

Ideally I think if there are n functions who provide the same
service.context.key they are called until one of them returns a none
null value (though I'm not sure this is possible).

I hope the above is not too confusing else please tell me and I'll try
to rephrase it.

Tom

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