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From "Davor Hrg (JIRA)" <...@tapestry.apache.org>
Subject [jira] Commented: (TAPESTRY-1798) Injection via Marker Annotations
Date Wed, 03 Oct 2007 06:48:50 GMT

    [ https://issues.apache.org/jira/browse/TAPESTRY-1798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12532012

Davor Hrg commented on TAPESTRY-1798:

some thoughts....

when we need a specific implementation of a service...

Service binder could add a marker automaticaly,
the marker would be impl class. 
service binder can have a method to add additional markers

using impl class as a marker can rise issues I'm nota aware currently...

> Injection via Marker Annotations
> --------------------------------
>                 Key: TAPESTRY-1798
>                 URL: https://issues.apache.org/jira/browse/TAPESTRY-1798
>             Project: Tapestry
>          Issue Type: New Feature
>          Components: tapestry-ioc
>    Affects Versions: 5.0.5
>            Reporter: Howard M. Lewis Ship
> Currently in IoC, when injecting a service, you are limited to two options:
> - Inject by type, assuming exactly one match
> - Inject by explicit service id
> In a fully featured system both of these are imperfect.
> When you take into account the idea that there will be overrides for built in services,
then you can't rely on their being just a single match.  That's what the Alias service in
tapestry-core is all about: contributing to the MasterObjectProvider to handle overrides.
Unfortunately, contributions to Alias are clumsy, as they have to rely on @InjectService for
> Having to know the service id is a problem, since service ids are not refactoring safe:
refactoring the service interface name will likely change the service id, but @InjectService
annotation values will still point to the old name.
> Imagine instead a marker annotation; no attributes, attached to a type.  Maybe it's attached
to the service implementation class, maybe its specified to the ServiceBinder.
> When injecting, the parameter type and annotations are checked for any known marker annotation
 (all the marker annotation will be identified at Registry start up).  The parameter type
is matched against services with the marker, at must be unique for just those services.
> An idiom involving a nested annotation named "Local" is likely, thus:
> public class MyModule
> {
>   @interface Local { }
>   @MarkedBy(Local.class)
>   public MyService buildMyService(@Local OtherService other) { ...
> }
> I'm fairly certain Guice has something quite similiar.
> The question is: can we get rid of service ids entirely?

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