On Thu, May 30, 2013 at 12:37 PM, tetsuo <[email protected]> wrote: > -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:
while i am also not a fan of having component generified i do believe the example below is a bit contrived. first, i hope most people do not use PropertyModels because they are not compile-time-safe. there are plenty of project that implement compile-time-safe models, personally i prefer https://github.com/42Lines/metagen to using proxy-based solutions. further, i hope even less people use compound property models. they are even more unsafe then property models and make your code even more fragile. i would hate to refactor code that uses CPMs. > 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. but how often do you declare a form component without adding any validators to it? the generic type of component also makes sure you add the correct validator. for example it wont let you add a validator that expects strings to a component that produces integers. also, not sure why you are replicating the model in Button. first, the Button uses its model to fill its label; secondly, in real code the model would be in a final var or field that things like onsubmit can access easily. -igor > > - 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 <[email protected]>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 >>
