[jira] [Commented] (WICKET-3805) Change Component#visitParents to enable visitors of any type

["Emond Papegaaij (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/WICKET-3805?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13204788#comment-13204788 ] 

Emond Papegaaij commented on WICKET-3805:
-----------------------------------------

I think the correct signature (if Java would have permitted it) should be:
 public final <R,C extends Component & T, T> R visitParents(final Class<T> c, final IVisitor<? super C, R> visitor)

The problem is that java does not allow intersection types with type parameters. So we have to choose between 'C extends T' or 'C extends Component'. I think C extends T is the best option, but this makes it impossible to use a visitor on Component if T is an interface:
 public final <R, T> R visitParents(final Class<T> c, final IVisitor<? super T, R> visitor)

 Another option is 2 methods, one for interfaces and one for components, so add this one:
 public final <R, T> R visitParentContainers(final Class<?> c, final IVisitor<? super MarkupContainer, R> visitor)

In either case, it is important to use '? super X', because it allows you to reuse visitors for which C is bound to a superclass (just as with Comparator).
                
> Change Component#visitParents to enable visitors of any type
> ------------------------------------------------------------
>
>                 Key: WICKET-3805
>                 URL: https://issues.apache.org/jira/browse/WICKET-3805
>             Project: Wicket
>          Issue Type: Improvement
>          Components: wicket
>    Affects Versions: 1.5-RC4
>            Reporter: Pedro Santos
>            Priority: Minor
>             Fix For: 6.0.0
>
>         Attachments: WICKET-3805.patch
>
>
> The generic type of c accepts any type, but the one in IVisitor restrict it to Components. 
> Comonent#visitParents(final Class<?> c, final IVisitor<Component, R> visitor)

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