$ cat foo.rb
module Stock
  STOCK_LIST = 'I am groot'
end

module Stock
  class Holder
    def initialize
      puts STOCK_LIST
    end
  end
end

class Stock::Holder2
  def initialize
    puts STOCK_LIST
  end
end

Stock::Holder.new
Stock::Holder2.new


$ ruby foo.rb
I am groot
foo.rb:15:in `initialize': uninitialized constant Stock::Holder2::STOCK_LIST (NameError)
	from foo.rb:20:in `new'
	from foo.rb:20:in `<main>'