[Xotcl] Precedence Order

[Scott Gargash]

Gustaf Neumann <neumann at wu-wien.ac.at> wrote on 09/04/2006 03:50:42 AM:

> Scott,
> 
> you can achieve the precedence you are wanting  by adding multiple 
> superclasses to Derived.
> In the forthcoming version (which will be named 1.5), you can even use 
> "superclass add" like
> in the following example.

Thanks, but in my particular case I don't have knowledge of Derived, only 
Base.  By that, I mean I'm actually adding BaseMixin (the HW simulator) to 
Base (the HW) before Derived has even been created.  I'd like for Derived 
to remain ignorant of BaseMixin because BaseMixin only exists for testing 
purposes.  I prefer to avoid having code paths that exist only for testing 
purposes. (Which mixins are particualrly well-suited for).

My current solution is to make Derived a mixin as well.  This then forces 
it to the head of the precedence order regardless of the existence of 
BaseMixin so I don't have different code paths for BaseMixin vs. Base.  It 
works, but it's not really correct from a design standpoint. Derived 
should be a derived class (it's a unique type), not a mixin.

This is what I meant about the current precedence order breaking 
encapsulation.  I wish to modify a single class, but the precedence order 
makes it be global.  In order to get things to work,  I have to distribute 
knowledge of BaseMixin to places in the hierarchy that (I believe) 
shouldn't have to know or care.

What's the scenario where it's desireable for BaseMixin to be ahead of 
Derived?
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