[jira] [Updated] (WICKET-3441) org.apache.wicket.util.lang.PropertyResolverConverter Type Erasure leads to Sloppy Typing

["Attila Király (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/WICKET-3441?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Attila Király updated WICKET-3441:
----------------------------------

    Attachment: fix-WICKET-3441.patch

Attaching patch against current trunk.

Patch contains fix for the issue and 2 new unit tests. The tests fail with the original implementation and pass with the new one.

> org.apache.wicket.util.lang.PropertyResolverConverter Type Erasure leads to Sloppy Typing
> -----------------------------------------------------------------------------------------
>
>                 Key: WICKET-3441
>                 URL: https://issues.apache.org/jira/browse/WICKET-3441
>             Project: Wicket
>          Issue Type: Bug
>          Components: wicket-core
>    Affects Versions: 1.5-RC1
>         Environment: all
>            Reporter: Richard Emberson
>            Priority: Minor
>         Attachments: fix-WICKET-3441.patch
>
>
> There seems to be some problems with the
> org.apache.wicket.util.lang.PropertyResolverConverter convert method
> that the Java compiler lets slip because of type erasure.
> To show this, lets let the convert method had type parameterized arguments:
> public <OT, CT> Object convert(OT object, Class<CT> clz)
> and the converter is then typed:
>   IConverter<CT> converter = converterSupplier.getConverter(clz);
> then the block of code:
>   else if (clz == String.class) {
>     return converter.convertToString(object, locale);
>   }
> has an issue because the convertToString expects object to have
> type CT. Because of type erasure, the Java compiler lets this
> slip by. In addition, since the class type is String, the
> converter used is just the ConverterLocator,DefaultConverter
> whose convertToString method ends up calling
>     return (String)Objects.convertValue(value, String.class);
> which, when nothing can be found to convert to a "known" value
> simply returns the value parameter. Again, all this is allowed
> because the Java compiler gets sloppy due to type erasure.
> But calling Objects.convertValue is just what the block of code
> following the above convert method code does:
>   else {
>     try {
>      return Objects.convertValue(object, clz);
>     } catch (RuntimeException ex) {
>      // ignore that try it the other way
>     }
>     // go through string to convert to the right object.
>     String tmp = converter.convertToString(object, locale);
>     return converter.convertToObject(tmp, locale);
>   }
> So, the previous block of code:
>   else if (clz == String.class) {
>     return converter.convertToString(object, locale);
>   }
> can be removed 1) allowing for correct typing and 2) with the
> same results.
> Also, if one examines the code:
>     // go through string to convert to the right object.
>     String tmp = converter.convertToString(object, locale);
>     return converter.convertToObject(tmp, locale);
> one sees that this has the same sloppy typing as the code block
> just remove, that is:
>     return converter.convertToString(object, locale);
> Again, object is of type OT while the convertToString method
> of the IConverter is expecting a type of CT.
> The fix is to use an IConverter of the type of OT to convert to
> String and then the IConverter of type CT to convert to the
> return object:
>     // go through string to convert to the right object.
>     IConverter<OT> converterForObj =
>         converterSupplier.getConverter(object.getClass());
>     String tmp = converterForObj.convertToString(object, locale);
>     return converter.convertToObject(tmp, locale);
> This is now correctly typed.
> I noticed this because there is rather more theory behind Scala's
> type system than Java's so that the Scala compiler complained about
> the attempt to sneak around the type erasure.

--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira