From: "Hal E. Fulton" <hal9000@...>
Date: 2001-11-18T10:10:17+09:00
Subject: [ruby-talk:25735] Parametric classes

I'm in the awkward position of having
written some code months ago and
then forgotten the underlying principle.

I was trying to "parameterize" classes
and set class variables appropriately.

This is a fragment that I got to work...
but, reading it, I feel as if it were 
someone else's code.   :0

The confusing part is passing in the
parent class to Class.new -- this is
a parameter to the initialize method,
but it's not used in my code.

Can someone comment on how this
works?

Hal


class Class

  def initialize(parent,&block)
    class_eval(&block)
  end

end


class Nationality

  def Nationality.native_lang
    class_eval("@@native_lang")
  end

  def Nationality.native_lang=(x)
    class_eval("@@native_lang = #{x}")
  end

  #...

end


Australian = Class.new(Nationality) do
  @@native_lang = "English"
end

Brazilian = Class.new(Nationality) do
  @@native_lang = "Portuguese"
end


t = Australian.new
p Australian.native_lang  # "English"
p Brazilian.native_lang   # "Portuguese"
p t.class                 # Australian
p t.is_a? Nationality     # true