From: Logan Capaldo <logancapaldo@...>
Date: 2006-02-07T06:25:12+09:00
Subject: Re: inheritence of aliases methods - suprise!


On Feb 6, 2006, at 4:06 PM, ara.t.howard@noaa.gov wrote:

>
> this suprised me today:
>
>     harp:~ > cat a.rb
>     class A
>       def assertion
>         raise NotImplementedError
>       end
>       alias_method "assertion?", "assertion"
>     end
>
>     class B < A
>       def assertion
>         true
>       end
>     end
>
>     B::new.assertion?
>
>
>     harp:~ > ruby a.rb
>     a.rb:3:in `assertion?': NotImplementedError (NotImplementedError)
>             from a.rb:14
>
>
> this only way i can seem to make this work is through some  
> self::inherited
> hacks or to actually define assertion? in the base class.  is there  
> no clean
> way to inherit aliases?
>
> regards.
>
> -a
>
> -- 
> happiness is not something ready-made.  it comes from your own  
> actions.
> - h.h. the 14th dali lama
>

This makes sense, If you consider the common idiom of alias'ing a  
method to wrap additional functionality around it. If alias(_method)  
didn't work like that you couldn't use it like this. alias_method  
doesn't work like assignment in ruby, its more like it creates a new  
method with the same source as the original method.

As a poorly conceived alternative:

% cat a.rb
class Class
   def shallow_alias(new_name, current_name)
     self.module_eval <<-END
     def #{new_name}(*args, &block)
       #{current_name}(*args, &block)
     end
     END
   end
end

class A
   def assertion
     raise NotImplementedError
   end
   shallow_alias "assertion?", "assertion"
end

class B < A
   def assertion
     true
   end
end

B.new.assertion?

% ruby a.rb
%