The 'self type' proposal for Java is what is needed here, not method
chaining:
public class Base {
public This setBaseStuff() { /* ... */ return this; }
}
public class Sub extends Base {
public This setSubStuff() { /* ... */ return this; }
}
The 'This' (or 'this') used as a return type means the actual type of
the instance, enabling situations like this to work.
Method chaining is very hard to follow (and I oppose it), as everyone
has already learnt the rule that you can't invoke a method on a void.
Stephen
On Feb 14, 4:14 am, Jeff Grigg <jeffgr...@charter.net> wrote:
> After listening to recent episodes, I've been working my way back to
> earlier episodes, and I keep tripping over discussions of Matthias
> Ernst's "Chaining: A Modest Language Proposal" -- which would make the
> compiler enable a method chaining / "fluid interface" convention on
> methods returning the void type.
>
> I'm also somewhat bothered by the idea of reinterpreting void return
> types, but I think it will be helpful to consider the cases where
> usage would be simplified or fixed by his proposal. So I posted two
> code examples on my blog:
>
> http://jeffgrigg.wordpress.com/2009/02/14/method-chaining-good-for-java/
>
> Briefly, given these two "Builder" classes:
> public class Base {
> public Base setBaseStuff() { /* ... */ return this; }
> }
> public class Sub extends Base {
> public Sub setSubStuff() { /* ... */ return this; }
> }
> This code works:
> new Sub().setSubStuff().setBaseStuff();
> But this code doesn't compile:
> new Sub().setBaseStuff().setSubStuff();
>
> The problem is that when you use method chaining on classes that
> extend other classes and which add methods, you MUST always call
> subclass methods before calling superclass methods -- otherwise it
> won't compile. In non-trivial examples, it gets harder and harder for
> the class' users to follow these rules.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "The
Java Posse" group.
To post to this group, send email to javaposse@googlegroups.com
To unsubscribe from this group, send email to
javaposse+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/javaposse?hl=en
-~----------~----~----~----~------~----~------~--~---
