Question

I have a module A:

module A
  extend self
  attr_accessor :two, :four
  ONE = "one"
  @two = "two"
  @three = "three"
  @@four = "four"
  @@five = "five"
  def six
    "six"
  end
end

And I require it inside another file:

require 'a'
include A
p ONE     # => "one"
p two     # => nil
p A.two   # => "two"
p three   # => error
p four    # => nil
p five    # => error
p six     # "six"

It seems like any class variable either gives me an error or nil unless I specifically scope it with the module name. I thought using include A would prevent that. How do I export these class variables so that I can reference them directly as two instead of having to use A.two?

Answer 1

if you define variables at class/module level then it is a class instance variable not a instance variable. we are setting getter methods with ||= because modules don’t have initialize method;

module A
  ONE = "one"

  attr_writer :two

  def two
    @two ||= "two"
  end

  def three
    @@three ||= "three"
  end

  def three=(val)
    @@three = val
  end
end

Then you can use methods directly;

include A

p two
p three
two = 2
three = 3
p two
p three