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From: Patrick Roemer <sangamon@netcologne.de>
Newsgroups: comp.lang.java.programmer
Subject: Re: can this be done with generics?
Date: Tue, 26 Nov 2013 12:03:42 +0100
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Responding to Robert Klemme:
> On 25.11.2013 12:59, Patrick Roemer wrote:
>> Responding to Andreas Leitgeb:
> 
>>> Is there a way to use *generics* for the methods of class Foo such that
>>> each foo#() returns the *static* type on which the compiler saw it
>>> applied?
>>
>> Just a naive attempt... Not sure if this matches your use case and
>> requirements - this will only work for a one-level hierarchy with an
>> abstract root class and will probably require some ugly gymnastics
>> inside the Foo method implementations:
> 
> The approach is all but naive.  And it can actually be made to work with 
> deeper hierarchies in a type safe way.  There is only a single 
> @SuppressWarnings("unchecked") here:
> 
> package inh;
> 
> public class Foo<T extends Foo<?>> {
> 
>      public T foo() {
>          System.out.println(getClass().getName() + " in foo()");
>          return self();
>      }
> 
>      @SuppressWarnings("unchecked")
>      protected final T self() {
>          return (T) this;
>      }
> 
>      public static void main(String[] args) {
>          new Baz<Baz<?>>().foo().baz().bar();
>          new TheEnd().foo().last().baz().bar();
>      }
> 
> }

Very nice. The cast just manifests an implicit assumption, so I think
it's justified here. The wildcards are somewhat disconcerting - but
certainly better than not having a general solution at all. :)

Best regards,
Patrick