[DS] Create separate Service annotation

bjhargrave commented 13 years ago

Original bug ID: BZ#2140 From: Felix Meschberger <fmeschbe@adobe.com> Reported version: R4 V4.3

bjhargrave commented 13 years ago

Comment author: Felix Meschberger <fmeschbe@adobe.com>

The current draft defines a "service" attribute on the component annotation which defaults to all directly implemented interfaces of the class

I think it would be better to separate more between components and services and create a separate Service annotation. If just the Component annotation is present, its not registered as a service With the Service annotation its possible register the component as a service. The Service annotation should have a class or value attribute. If that is left empty, the component is registered for all interfaces or all directly implemented interfaces (whether all or all directly implemented might be another discussion).

Especially the default of not specifying the service attribute on the Component is error prone as its not intuitive. Not specifying something should mean: this is no service :)

For example the Apache Felix SCR annotations has such a separate Service annotation:

http://felix.apache.org/site/scr-annotations.html#SCRAnnotations-Service

bjhargrave commented 13 years ago

Comment author: @pkriens

I really prefer to keep the additional types minimal. In my experience the current model work pretty well

@ Component -> default all implemented interfaces (except ScalaObject) @ Component(service=X.class) -> only X service @ Component(service={}) -> no service

Seems to be easy to read and since a service is an integral part of the component I do not see a good reason to separate them?

bjhargrave commented 13 years ago

Comment author: Felix Meschberger <fmeschbe@adobe.com>

Although the service functionality clutters the @ Component annotation, I could probably live with it. But I would prefer the default for a missing attribute to be a no-service component.

The problem really is the convenience case of just declaring a component a service of the implemented interfaces. Here the separate annotation comes in very handy:

-- No annotation --> no service -- @ Service() (empty value) --> all implemented interfaces -- @ Service(X.class, Y.class) --> explicit list

bjhargrave commented 13 years ago

Comment author: Richard Hall <heavy@ungoverned.org>

Ultimately, I agree with Felix. iPOJO uses separate annotations too, although in iPOJO's case it is @ Component and @ Provides, which fit nicely with @ Requires. From my point of view, this is a nicer separation of concerns.