From: Trans <transfire@...>
Date: 2005-04-15T03:49:35+09:00
Subject: Re: class locals as class methods

Mark Hubbart wrote:
> I think meta-programming would suffer.
>
> # a Foo that is sort of like a Bar
> class FooBar < Foo
>   bar_methods = Bar.instance_methods - self.instance_methods
>   bar_methods.each{ ... }
> end
>
> FooBar.bar_methods => ?????
>
> It would be like penalizing people for using metaprogramming
techniques :(

Hmm... I would think that code would work just fine. I'm not suggesting
that local vars be displaced, if that is what you mean, only that they
overlap. So a class local var is a class method is a class local var.
It is the same namespace afterall (i.e. self resoves to the same thing)
so that's okay too. Am I understanding your example?

For reference I tried:

  module Bar
    def a ; ; end
    def b ; ; end
    def c ; ; end
  end

  class Foo
    def x ; ; end
    def y ; ; end
    def z ; ; end
  end

  class FooBar < Foo

    # local
    foo_bar = Bar.instance_methods - self.instance_methods
    p foo_bar

    # class
    def self.bar_methods
      Bar.instance_methods - self.instance_methods
    end

  end

  p FooBar.bar_methods

with the result:

["c", "b", "a"]
["c", "b", "a"]

> Perhaps, if you just want to set attributes:
>
> class Class
>   def set(name, value)
>     self.class_eval "def self.#{name}() @@#{name} end"
>     self.class_eval "@@#{name} =
ObjectSpace._id2ref(#{value.object_id})"
>   end
> end
>     ==>nil
> class Foo
>   set :foo, "yep!"
> end
>     ==>"yep!"
> Foo.foo
>     ==>"yep!"
>
> I'm sure it could be condensed even further, if needed.

Sure, that's one fair way. There are a number of ways to do it, like
the simple first examples I gave. But all of them seem, well,
contrived. In other words, there's no sort of obvious standard to this
kind of thing. And worse to me, the solutions all look like they've
been hit up with an ugly stick ;-)

> Off topic now, I thought there was an equivalent of
> #instance_variable_set for class variables? It would seem not. I
> wonder why.

Hmm... I don't know, maybe b/c this is less characters?

  Klass.class_eval { @@x = "foo" } 

Thanks,
T.