From: Robert Dober <robert.dober@...>
Date: 2007-05-03T13:56:47+09:00
Subject: Re: simple subclass question

On 5/3/07, Gary Wright <gwtmp01@mac.com> wrote:
>
> On May 2, 2007, at 2:57 PM, Ball, Donald A Jr (Library) wrote:
> > In the superclass, I want a chunk of code that
> > initializes a class instance variable in itself and each of its class
> > descendents.
>
> You can use #inherited to trigger your own class initialization:
>
> class Base
>    class <<self
>      def inherited(other)
>        other.instance_eval { initialize_class }
>      end
>      def initialize_class
>        @foo = 42
>      end
>      attr_accessor :foo
>    end
>    initialize_class
> end
>
> class Subclass < Base
>    puts "foo is #{@foo}"       # 42
> end
>
> puts Subclass.foo             # 42
> puts Class.new(Base).foo      # 42
>
>
>
> Gary Wright

Wow that scales much better than mine Gary, nice.
However maybe you want to inherit @foo dynamically, that is
I suggest this slight adaptation of Base

529/29 > cat inherited.rb && ruby inherited.rb
# vim: sts=2 sw=2 expandtab tw=0 nu:
class Base
  @foo = 42
  class <<self
    def inherited(other)
      other.instance_eval { initialize_class }
    end
    def initialize_class
      @foo = superclass.instance_variable_get("@foo")
    end
    attr_accessor :foo
  end
end

class Subclass < Base
  puts "Sub foo is #{@foo}"       # 42
end
Base.foo = 1764
class Another < Base
  puts "Another foo is #{@foo}"       # 42
end

puts Subclass.foo             # 42
puts Class.new(Base).foo      # 42
Sub foo is 42
Another foo is 1764
42
1764

What do you think, anyway the two behaviors might be what you want, I
actually need the second behavior.

Cheers
Robert


-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw