From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2006-07-25T07:50:11+09:00
Subject: Re: I'll have the duck!

Daniel DeLorme wrote:
> benjohn@fysh.org wrote:
>> I also like it because I don't think that there's anything especially
>> fundamental about classes. With predicate classes, all you're really
>> saying is that "if I've got something that can do x and y, then I know
>> that I can equally validly think of it as something that can do z".
> 
> The concept really piqued my interest, and since ruby gives us such nice
> metaprogramming abilities, why not do it?
> 
> 
> module DuckTyping
>   @@quacks = Hash.new{ |h,k| h[k] = {} }
> 
>   def ducktype(*reqs, &block)
>     o = Object
>     before = o.methods
>     o.class_eval(&block)
>     after = o.methods
> 
>     for methodname in (after - before)
>       @@quacks[methodname.to_sym][reqs] = 
> o.instance_method(methodname.to_sym)
>       o.send(:remove_method, methodname.to_sym)
>     end
>   end
> 
>   def ducktype_method(methodname)
>     @@quacks[methodname.to_sym].each do |reqs, m|
>       if reqs.all?{ |r| self.respond_to?(r) }
>         return m
>       end
>     end
>     return nil
>   end
> 
>   def method_missing(methodname, *args, &block)
>     if m = ducktype_method(methodname)
>       m.bind(self).call(*args, &block)
>     else
>       super
>     end
>   end
> end
> Object.module_eval{ include DuckTyping }
> 
> 
> ducktype :quack do
>   def quack_loudly
>     quack.upcase
>   end
> end
> 
> 
> class Duck
>   def quack
>     "quack!"
>   end
> end
> 
> class Dog
>   def bark
>     "woof!"
>   end
> end
> 
> Duck.new.quack_loudly #=> "QUACK!"
> Dog.new.quack_loudly  #=> NoMethodError
> 
> 
> nifty?

Isn't this stuff used i Aspect Oriented Programming as well? I only know 
what I've read in the RCR, so I'm not sure.


Cheers,
Daniel