From: transfire@...
Date: 2006-06-08T23:48:43+09:00
Subject: Re: Why the lack of mixing-in support for Class methods?


ara.t.howard@noaa.gov wrote:
> indeed.  still - i see it being a bit anti POLS from someone's perspective,
> that's all.

Fair enough. No doubt it will come with it's own set of considerations
with which we progammers will have to become familiar.

> > Nonethesless, I agree with Matz. I think a simple alternative call is
> > the prefect compromising solution. Perhaps:
> >
> > class C
> >   inherit M
> > end
>
> i have my own impl ;-)
>
> > Also, This post is kind of timely, I'be been preparing a post with example's
> > from Nitro on the extensive need of this behavior --you should see the many
> > "hacks" being used to accomplish this there --I think at least three
> > different techinqes are being used throughout dozens of components.
>
> the one issue i see is with stateful methods - we don't currently have
> 'inheritable state'.  eg
>
>    module M
>      class << self
>        attr 'foo'
>      end
>      @foo = 42
>    end
>
>    class A
>      inherit M
>    end
>
>    class B < A
>    end
>
>
>    p M.foo #=> 42
>    p A.foo #=> nil
>    p B.foo #=> nil
>
>    A.foo = 'forty-two'
>
>    p M.foo #=> 42
>    p A.foo #=> 'forty-two'
>    p B.foo #=> nil
>

I think one would need to set that up oneself using a class variable.
Rather I would expext this it to behave like it does, just as with a
class:

  class X
    def self.x
      @x
    end
    @x = 10
  end

  class Z < X
  end

  X.x  #=> 10
  Z.x  #=> nil

> traits addresses this.  eg this works
>
>    require 'traits'
>
>    class M
>      class_trait 'foo' => 42
>    end
>
>    class A < M
>    end
>
>    class B < A
>    end
>
>
>    p M.foo #=> 42
>    p A.foo #=> 42
>    p B.foo #=> 42
>
>    A.foo = 'forty-two'
>
>    p M.foo #=> 42
>    p A.foo #=> 'forty-two'
>    p B.foo #=> 'forty-two'
>

You bring up your traits library all the time ;) Actually all-in-all I
think it's pretty good. Unfortuately I have this one nagging problem
with it. I think the term 'traits' is a terrible misnomer. That may
seem silly but having done some study of prototype-base OOPS,
especially Self, traits are just a totlatlly different concept to me.
 
T.