Comment 1 Till Brychcy 2018-07-02 06:33:32 EDT

Still compiles in Eclipse4.8I20171217-2000
Reports errors in Eclipse4.8I20180112-2000

Further reduced example:

interface IXmlFileVersion<T> {
}

class VersionContainer<VERSION extends Enum<VERSION> & IXmlFileVersion<?>> {

    public static <T, VERSION extends Enum<VERSION> & IXmlFileVersion<T>> void toXml(VERSION version) {
    }

    public static <VERSION extends Enum<VERSION> & IXmlFileVersion<?>> void extractVersion(Class<VERSION> versionEnum) {
    }
}

public class VersionContainerTest {

    public void testToXml() {
        VersionContainer.toXml(ETestDataVersion.VERSION1);
    }

    public void testExtractVersion() {
        VersionContainer.extractVersion(ETestDataVersion.class);
    }

    public static enum ETestDataVersion implements IXmlFileVersion {
        VERSION1
    }
}

Comment 2 Till Brychcy 2018-07-02 06:53:24 EDT

Caused by commit ec76c89defa5f96571519ef98af5fe717abfdb09 for bug 528970.

Comment 3 Andrey Loskutov 2018-07-02 07:17:38 EDT

(In reply to Till Brychcy from comment #1)
>     public static enum ETestDataVersion implements IXmlFileVersion {
>         VERSION1
>     }

Just wondering why one would let enums (usually constants) implement a *generic* interface. Enums can't be generified AFAIK, and I guess this is the reason why one uses here raw IXmlFileVersion interface.

@Andreas: in the example, IXmlFileVersion T type is not used. I'm just curious, what is the purpose of T in the real code, and how enums are using this T? The only use in the example was in the static methods, which do not need to be in the enum itself. Are there other uses of T in the Enum itself?

Comment 4 Andreas Sewe 2018-07-02 08:56:10 EDT

(In reply to Andrey Loskutov from comment #3)
> (In reply to Till Brychcy from comment #1)
> >     public static enum ETestDataVersion implements IXmlFileVersion {
> >         VERSION1
> >     }
> 
> Just wondering why one would let enums (usually constants) implement a
> *generic* interface. Enums can't be generified AFAIK, and I guess this is
> the reason why one uses here raw IXmlFileVersion interface.
>
> @Andreas: in the example, IXmlFileVersion T type is not used. I'm just
> curious, what is the purpose of T in the real code, and how enums are using
> this T? The only use in the example was in the static methods, which do not
> need to be in the enum itself. Are there other uses of T in the Enum itself?

A bit more context:

We have a lot of things in our code base that can be versions and which need to be migrated from one version to the next. So you find types like

  enum EProjectConfigurationVersion implements XmlFileVersion<ProjectConfiguration>

or

   enum EAnalysisProfileVersion implements IXmlFileVersion<AnalysisProfile>

with constants like VERSION_1_0, VERSION_1_1, etc. Each individual enum constant implements a version-specific migrate(String) method that migrates the XML string, if necessary.

The type parameter T is used by the static toXml(T, VERSION extends Enum<VERSION> & IXmlFileVersion<T>) method to ensure that the enum VERSION_x_y constant passed as the second parameter knows how to migrate the payload type T passed as the first argument.

So, outside the test, we don't use IXmlFileVersion as a raw type -- and generified enums work quite well.

Hope this clarifies things.

Comment 5 Eclipse Genie 2022-07-17 19:42:17 EDT

This bug hasn't had any activity in quite some time. Maybe the problem got resolved, was a duplicate of something else, or became less pressing for some reason - or maybe it's still relevant but just hasn't been looked at yet.

If you have further information on the current state of the bug, please add it. The information can be, for example, that the problem still occurs, that you still want the feature, that more information is needed, or that the bug is (for whatever reason) no longer relevant.

--
The automated Eclipse Genie.