From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2005-12-16T00:57:40+09:00
Subject: Easy Duck-Typing

This will make it easier to add type checking to your methods. Let me 
know if you think the method belongs in Object or another class, rather 
than in the Kernel module.


   class Kernel
     def cast(obj, klass, method = nil)
       return obj if obj.kind_of? klass

       method = "to_#{method || klass.downcase}"

       unless obj.respond_to? method
         raise TypeError, "Can't convert #{obj.class} into #{klass}"
       end

       cast_obj = obj.send(method)

       unless ccast_obj.kind_of? klass
         raise TypeError, "#{obj.class}##{method} should return #{klass}"
       end

       return cast_obj
     end
   end


   class Klass
     def foo(arg)
       # Will raise an exception unless `arg' is
       # of type SomeKlass, or if it has a method
       # #to_some_klass that returns an object of
       # type SomeKlass
       arg = cast(arg, SomeKlass, :some_klass)
     end
   end


Is there an easy way to turn a CapitalizedName into a downcase_name? 
Right now I'm just downcasing the class name if no cast method name is 
explicitly provided, but I'm not sure that's enough.


Cheers,
Daniel