-1000!
This will be horrible! Even with the current API, most generics I have to
declare in my code don't add anything to type safety. For example:
add(new Form<Person>("form", new CompoundPropertyModel<Person>(new
PropertyModel<Person>(this, "person")))
.add(new TextField<String>("name"))
.add(new TextField<Integer>("age"))
.add(new TextField<Double>("salary"))
.add(new Button("save", new PropertyModel<Person>(this,"person")){
public void onSubmit() {
repository.save((Person)getForm().getDefaultModelObject());
}
});
In my experience, this kind of code is fairly common in Wicket
applications. Every form component must be declared with a type, but none
has *any* kind of type safety gain.
- The property model uses reflection, so its type can't be verified by the
compiler (this.person could be anything, not just a Person).
- Generics will guarantee that the form model will be of type Person, but
since it's all declared inline, and the real model isn't verifiable, it
just adds lots of verbosity without any real gain.
- Most form components use the implicit model, that also uses reflection,
and also can't verify the actual type of the underlying property, at
compilation time. Even in runtime, *the type information is lost due erasure
*, so it can't use it to do any additional verification.
*- Worse, you can even declare the "name" TextField as <Integer> or
<Double> (while maintaining the 'text' attribute as String), and since
there is no type information at runtime, it doesn't matter. It won't even
throw an exception (it will just work normally).* In this case, the type
declaration is simply a lie.
Just pain, no gain. In my code, I sometimes just add a @SuppressWarnings(
"rawtypes") to the class, and remove all useless generic type declarations.
If everything will be required to declare them, I will have do it more
frequently.
That said, repeater components benefit greatly from generics. So do custom
models, validators, and converters. Or the rare cases that we explicitly
declare the form component model. But forcing everything to be
generic-typed will just make Wicket extremely verbose to use, with very
little benefit.
On Thu, May 30, 2013 at 4:00 AM, Martin Grigorov <mgrigo...@apache.org>wrote:
> Hi,
>
> I just pushed some initial work for [1] and [2] in
> branch generified-component-4930.
>
> So far it doesn't look nice.
>
> The added generics break somehow setMetaData/getMetaData methods - you can
> see compilation errors in Component and Page classes. I think it is caused
> by the anonymous instance of MetaDataKey ( new MetaDataKey<T>(type) {} ).
>
> Also the visit*** methods do not compile at the moment, but even if we find
> a way to fix their signature I think writing a visitor will become quite
> cumbersome.
> At the moment we have IVisitor
> and org.apache.wicket.util.iterator.AbstractHierarchyIterator which do the
> same job. The Iterator API is supposed to be simpler to write for the
> users. Maybe we can drop IVisitor ... ?!
>
> I'd like to ask for help with this task. It is supposed to be the biggest
> API break for Wicket 7.0. My current feeling is that the end result won't
> be very pleasant for the user-land code.
> For example the application code will have to do something like:
>
> WebMarkupContainer<Void> wmc = new WebMarkupContainer<>("id")
>
> It is not that much but we have to decide whether we want it.
> But first let's try to fix the compilation problems.
>
>
> 1. https://issues.apache.org/jira/browse/WICKET-4930 (Add generics to
> o.a.w.Component)
> 2.
>
> https://cwiki.apache.org/confluence/display/WICKET/Wicket+7.0+Roadmap#Wicket7.0Roadmap-Genericsfororg.apache.wicket.Component
>
