[ruby-talk:17001] Re: Method overloading (option) Was: Re:

On Thu, 28 Jun 2001, Yukihiro Matsumoto wrote:

> Hi,
> 
> In message "[ruby-talk:16972] Re: Method overloading (option) Was: Re:"
>     on 01/06/28, Hugh Sasse Staff Elec Eng <[e-mail]> writes:
> 
> |> If you give an object of wrong protocol, you'll get NameError (well,
> |
> |I'm not sure what you mean here.  (That could be because I'm implementing
> |a 'protocol' on top of UDP at the moment, so I'm see the word differently 
> |from you! :-))  Can you give an example of how a NameError can come from
> |passing the wrong object to a user defined method, without using type
> |dispatch, please?  This may help me see your Ruby Way.
> 
>   def split(obj)
>     a = []
>     len = obj.size
>     for i in 0...len
>       a.push obj[i]
>     end
>     a
>   end
> 
>   p split("abc")        # [?a, ?b, ?c]
>   p split([1,2,3])      # [1, 2, 3]
>   p split(:foo)         # -:3:in `split': undefined method `size' for :foo:Symbol (NameError)
>  
> the "split" takes any object that responds to "size" and "[]".  "size"
> and "[]" are protocol this case.

OK, thank you.  That is clear.  Now, one can add (I'm writing this
like a patch) :

    def split(obj)
      a = []
+     return a unless obj.respond_to?(:size)
+     return a unless obj.respond_to?(:[])
      len = obj.size
      for i in 0...len

and so on for the other methods one might use, but how does that get around
having to refer to methods in more than one place, that I asked about?  

I have a vague notion that it might be possible to have a scope based
obj.methods_called() method, which would return a list of symbols telling
which methods were used in this scope.

   return [] unless obj.methods_called.all? {|m| obj.respond_to?(m)}

or whatever.  Is this half-baked idea worth any further consideration?
> 
> 							matz.
> 
	Thank you
	Hugh