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copied!<p>Well, first of all... it's a really good idea to explain how <code>@@</code> variables work exactly. </p> <p><code>@@</code> variables are class variables that can be accessed on the instance context, say for example:</p> <pre><code>class Klass def my_klass_variable=(str) # self here points to an instance of Klass @@my_klass_variable = str end def my_klass_variable @@my_klass_variable end end Klass.new.my_klass_variable = "Say whaat?" # Note this is a different instance Klass.new.my_klass_variable # => "Say whaat?" </code></pre> <p>However this type of variables will incur also in the following result:</p> <pre><code>class OtherKlass < Klass; end Klass.new.my_klass_variable = "Howdy" # Note this is a different instance, and from the child class OtherKlass.new.my_klass_variable # => "Howdy" </code></pre> <p>Crazy behavior indeed. Another way to create Class variables, is defining instance variables on a method that starts with <code>self.</code>. For example:</p> <pre><code>class Klass def self.my_class_method @class_var = "This is a class var" end end </code></pre> <p>Why a <code>@</code> for class variables as well? Remember that <code>Klass</code> in this is an <em>instance</em> of the <code>Class</code> class, this will have its own instance variables, that at the end will be class variables for instances of <code>Klass</code>.</p> <pre><code>Klass.class # => Class Klass.instance_of?(Class) # => true k = Klass.new k.class # => Klass k.instance_of?(Klass) # => true </code></pre> <p>This is more safe for class variables (as they will have one copy of the variable, and not a shared one with child classes as well), and will behave as you are expecting to behave when using your example:</p> <pre><code>module Ammunition def self.included(base) base.class_eval do @ammo = [bullets] # where bullets come from any way? end end def self.unload p @ammo end end class Tank include Ammunition # Probably you meant that instead of Packagable @ammo += [shells] # I think you meant @ammo instead of @a end class Airplane include Ammunition # Probably you meant that instead of Packagable @ammo += [missiles, photon_torpedoes] # I think you meant @ammo instead of @a end </code></pre> <p>This code as pointed by others won't work (given there is no shells, missiles nor photo_torpedoes), but I think you can figure it out how to make it work by yourself.</p>

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