[Xotcl] implementing delegation in Xotcl?

Hi,

I have a very philosophical question :-)

I would like to replace inheritance by delegation for some classes' instances.

e.g: Class C -parameter {delegate} # instead of Class C -superclass D C c -delegate a

where a is an object of another class, say class A.

Delegation means that: - next should call the delegate's proc/instproc - set, instvar would give access to delegate's variables (this is one of the classical delegation mechanisms/behaviour I believe?)

I have tried 3 methods, but neither work!

1) with a filter on C, which branch the methods calls to the appropriate location. the filter is defined in init: C filter CFilter

C instproc CFilter args { ::set m [[self] info calledproc] [self] instvar delegate if { ([C info instprocs $m] != "") || ([[self] info procs $m] != "") } { puts "CFilter m=$m I do it myself" next } elseif { [info exists delegate] && ($m == "set" || $m == "instvar") } { puts "CFilter m=$m I delegate it to $delegate" eval $delegate $m $args } elseif {[info exists delegate] && [[$delegate info class] info instprocs $m] != ""} { puts "CFilter m=$m I delegate it to $delegate" eval $delegate $m $args } else { puts "I dont know (m=$m), I call next" next } }

2) with a mixin on c in init: [self] mixin [$delegate info class]

3) with both

=> problem with filter only (1) : - next does not work the way I want (it does not call the delegates) - set of delegates' variables works, but instvar don't

=> problem with mixin only (2) - as the delegate's class is the mixin, it's it's methods which are always called first (but I want the delegate's methods to be called only when not existing for the class or when calling next) - I need a method in the delegate's class for every method int the class - delegate's variables are not available, of course (since I only use the class of the delegate to inherit methods)

=> mixin+filter (3) (example below) : - instvar does not work

Does someone have ideas and opinions about this? Has someone already tried? I don't remeber having found something about it in Xotcl's papers (maybe I'm wrong?).

Thanks!