Trying to "inherit" class configuration and modify it

ruby-talk
1

This gist has a bigger example of what I'm trying to do, but just
understanding how to make the following short example work, and/or why
it doesn't, will probably get me through the bigger problem.

testit.rb:

require 'pp'
class A
  @@a = [7]
  def self.get_a
    @@a
  end
  def self.put_a
    pp @@a
  end
end
                                                                                                                                                       
class B < A
  @@a = A.get_a.dup
  @@a = [8]
  def self.put_a
    pp @@a
  end
end
                                                                                                                                                       
A.put_a
B.put_a
A.put_a

[wwalker@dogwood inherit_settings] $ ruby testit.rb
[8]
[8]
[8]

I would expect:
[7]
[8]
[7]

I don't see my error. I think that maybe dup() doesn't work on a class
variable, or that maybe class variables are not really class variables,
but are rather hierarchy variables that can only exist in one place in
an class and it ancestry?

···

--

Wayne Walker
wwalker@solid-constructs.com
(512) 633-8076
Senior Consultant
Solid Constructs, LLC

A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> > A: Top-posting.
> > > Q: What is the most annoying thing in e-mail?

2

Wayne Walker wrote in post #980677:

maybe class variables are not really class variables,
but are rather hierarchy variables that can only exist in one place in
an class and it ancestry?

That's exactly it. Class variables are something of a misfeature in
Ruby.

However, in Ruby everything is an object - including a Class. So you can
use a regular instance variable of the class itself. Just change all
'@@'s to '@' in your code, and it will work the way you want.

To access the value from an instance method, use

    self.class.get_a

(because 'class' is otherwise a keyword)

HTH,

Brian.

···

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