From: Robert Klemme <bob.news@...>
Date: 2005-04-16T18:39:35+09:00
Subject: Re: self


"Trans" <transfire@gmail.com> schrieb im Newsbeitrag 
news:1113449849.596475.60490@z14g2000cwz.googlegroups.com...
> 1) use a superclass rather than a module:
>
>  class MySuperClass
>    def self.do_something
>      puts "success"
>    end
>  end
>
>  class MyClass < MySuperClass
>    do_something
>  end

Did you verify that this works?  :-)

> 2) use extend instead of include:
>
>  module MyModule
>    def do_something
>      puts "success"
>    end
>  end
>
>  class MyClass
>    extend MyModule
>    do_something
>  end
>
> 3) get tricky with it and use append_features:
>
>  module MyModule
>    def self.append_features( aClass )
>      def aClass.do_something
>        puts "success"
>      end
>      super # must do this!
>    end
>  end
>
>  class MyClass
>    include MyModule
>    do_something
>  end
>
> I do not recommend the later though.

Here's what I do if I want to have a set of singleton methods available for 
all classes in a class hierarchy:

class Base
  module MySpecialClassMethods
    # make inheritance work:
    def inherited(cl) cl.extend MySpecialClassMethods end

    attr_accessor :bar
    def foo() "foo" end
    # other methods...
  end

  extend MySpecialClassMethods
end

class Derived < Base
end

>> Base.foo
=> "foo"
>> Derived.foo
=> "foo"

>> Base.bar = 1
=> 1
>> Base.bar
=> 1
>> Derived.bar
=> nil
>> Derived.bar = 10
=> 10
>> Derived.bar
=> 10
>> Base.bar
=> 1

The nice thing is that there is just one copy of those method definitions 
plus you can change them or add new ones later and automatically all classes 
in the hiearchy have them.

Some background: you need to use the trick with #inherited() because 
singleton methods do not inherit along the class hierarchy because the class 
of all classes is Class.

>> Base.class
=> Class
>> Derived.class
=> Class

Kind regards

    robert