[Vala] I'm missing Java's anonymous classes

[Jim Peters <jim uazu net>]

This is an inconvenience rather than a project-killer, but still ...

I know that the Java page suggests that instead of using anonymous
classes, to use delegates, but it just doesn't work out as hoped.  
For example (much simplified):

  public abstract class Widget : Object {
     public abstract void relayout();
  }

I want to write this but it's not allowed:

  var xx = new Widget() {
     public void relayout() { ... }
  };

Switching to delegates:

  public class Widget {
     public delegate void RelayoutDelegate();
     public RelayoutDelegate relayout;    
     public Widget(RelayoutDelegate arg) {
         relayout = arg;  
     }
  }

  var xx = new Widget(
     () => { ... }
  );

This seems okay so far, but here comes the killer:

  public class Display : Widget {
     public Display() {
        base(relayout_imp);
     }
     private void relayout_imp() { ... }
  }

This crashes when relayout() is called because the 'relayout_imp'
argument to the constructor needs 'self' but 'self' hasn't been
initialised yet (so is NULL).

Any attempt to work around this makes the whole thing more verbose and
more error-prone -- for example, assigning the delegate after
construction means that the delegate can't be called during
construction -- and the whole thing just gets into a big tangled mess.

So I've gone back to Java style, only I have to create separate dummy
classes now to provide the callbacks.

The code is a lot more readable when the callbacks are inline (either
as delegates or as an anonymous class), but I really can't see a
sensible and safe way of doing this in Vala.  (In real life I have
several methods that may need overriding, and several layers in the
object hierarchy).

Any thoughts on this?

Jim

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