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From "Robert Zeigler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (TAP5-1493) Property expressions on properties that are covariant on a base class use the type of the base class property, not the covariant subclass
Date Fri, 01 Apr 2011 20:23:05 GMT

    [ https://issues.apache.org/jira/browse/TAP5-1493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13014813#comment-13014813
] 

Robert Zeigler commented on TAP5-1493:
--------------------------------------

Just ran into exactly this problem this week. In my case:

interface Foo {}
interface Bar extends Foo{}

interface Baz {
   Foo getFoo();
}

interface Qux extends Baz {
   Bar getFoo();
}


class AbstractClass implements Baz {...}
class MyClass extends AbstractClass implements Qux {
   Bar getFoo();
}

Then property expressions that explicitly use MyClass as the root and attempt to access foo.barSpecificProperty
were failing with "Foo doesn't have a property 'barSpecificProperty'".


> Property expressions on properties that are covariant on a base class use the type of
the base class property, not the covariant subclass
> -----------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: TAP5-1493
>                 URL: https://issues.apache.org/jira/browse/TAP5-1493
>             Project: Tapestry 5
>          Issue Type: Bug
>          Components: tapestry-core, tapestry-ioc
>    Affects Versions: 5.3.0, 5.2.5
>            Reporter: Howard M. Lewis Ship
>            Priority: Critical
>
> public abstract class AbstractFoo
> {
>  public abstract AbstractBar getBar();
> }
> public class Foo extends AbstractFoo
> {
>  public Bar getBar();
> }
> Here property bar is covariant; the subclass (Foo) changes the type of the return value
(from AbstractBar to just Bar). Assuming that Bar is a subclass of AbstractBar, that's fine.
> The bug is that in this circumstance, the PropertyConduitSource sees the type of
> property "bar" of class Foo as AbstractBar, not Bar.
> Interestingly, a little debugging showed that the getter method for property bar was
"public AbstractBar Foo.getBar()" ... in other words, much like with Generics, covariant return
types may be largely
> a fiction of the compiler inserting the necessary casts in place.

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