From: Robert Klemme <bob.news@...>
Date: 2004-11-29T23:57:49+09:00
Subject: Re: Getting a callback whenever a class method is added to a class or its children?


"Francis Hwang" <sera@fhwang.net> schrieb im Newsbeitrag
news:47FE7E9A-420E-11D9-960B-000A95DBF456@fhwang.net...
> Is there a way to capture whenever a class method is added either to a
> base class or its children? For example, if my code is
>
> class A
>    def self.some_method
>      ...
>    end
> end
>
> class B < A
>    def self.some_method
>      ...
>    end
> end
>
> I want to be notified twice. Defining A.singleton_method_added only
> seems to work for the definition of A.some_method, but won't catch the
> definition of B.some_method.

Of course, as it's defined for A only and not for B.  You can define
singleton_method_added in class Class - then it will catch *all* singleton
methods defined for class instances.


class Class
  def singleton_method_added(sym)
    puts "singleton added to #{self}: #{sym}"
  end
end

class A
   def self.some_method
     # ...
   end
end

class B < A
   def self.some_method
     # ...
   end
end


Or you can define a module for this:

module SingletonAware
  def singleton_method_added(sym)
    puts "singleton added to #{self}: #{sym}"
  end
end

class A
   extend SingletonAware

   def self.some_method
     # ...
   end
end

class B < A
   extend SingletonAware

   def self.some_method
     # ...
   end
end

With a bit more magic you can even safe the "extend SingletonAware" for
class B.

Kind regards

    robert