From: Christoph <chr_news@...>
Date: 2002-09-28T01:43:01+09:00
Subject: Re: adding overload to ruby


"ts" wrote
...
> C> It would be helpful  (I have an idea but ...) if you could
> C> describe what your next_method call does ...
>
>  Same than Dylan, except that I don't give the possibility to change the
>  dispatch at runtime (i.e. #next_method take 0 argument) which is, at least
>  for me, a bad thing

Thanks!

>
....
> pigeon% cat d.rb
> #!./ruby -w
> class B < Array; end
> module M
>    def a(B b) end
> end
>
> class A
>    include M
>    def a(Array a) end
> end
> pigeon%
>
> pigeon% d.rb
> ./d.rb:9: Possible ambiguous call M [B] -- A [Array] (NameError)


Isn't this the same ambiguity you get with regular inheritance?

---
class B < Array; end

class  ProxyA
    def a(B b ) end
end

class A < ProxyA
   def  a(Array b) end
end

obj = A,new
obj.a( Array.new(1) )  # not ambiguous
obj.a(B.new(1) )          # ambiguous
# with the rule(d) of my previous post the ambiguity
# would be resolved to a call of  A#a(Array)
---

If you buy into the evil multi-dispatch you either
have live with occasional ambiguity-errors or
use some sort  of ambiguity resolution mechanism.

/Christoph