Question

Please help me out.

I need to use the same bunch of attributes in many classes. I would suggest to create module with predefined attributes and extend this module in every class

module Basic
 @a=10
end

class Use
 extend Basic
 def self.sh
  @a
 end
end

puts Use.sh

but the output is empty. It seems like I missed something.

Maybe there is a better way to do that?

Your thoughts?

Answer 1

It’s all about the self:

module Basic
  @a=10
end

has self evaluating to Basic. You want it to evaluate to Use when the latter is extended:

module Basic
  # self = Basic, but methods defined for instances
  class << self
    # self = Basic's eigenclass
    def extended(base)
      base.class_eval do
        # self = base due to class_eval
        @a=10
      end
    end
  end
end

class Use
  # self = Use, but methods defined for instances
  extend Basic # base = Use in the above
  class << self
    # self = Use's eigenclass
    def sh
      @a
    end
  end
end

Use.sh # 10