Coding Conventions

Do not use Class Instance Variables

They are not doing what one would expect and they violate the Liskov Principle

Example:

[136] pry(File):1> class A
[136] pry(File):1*   cattr_accessor :a 
[136] pry(File):1* end  
=> [:a]
[137] pry(File):1> class B < A
[137] pry(File):1*   cattr_accessor :a
[137] pry(File):1* end  
=> [:a]
[138] pry(File):1> class C < A
[138] pry(File):1*   cattr_accessor :a
[138] pry(File):1* end  
=> [:a]
[139] pry(File):1> C.a
=> nil
[140] pry(File):1> A.a = 42
=> 42
[141] pry(File):1> C.a
=> 42
[142] pry(File):1> A.a
=> 42
[143] pry(File):1> B.a
=> 42
[144] pry(File):1> B.a = 84
=> 84
[145] pry(File):1> A.a
=> 84
[146] pry(File):1> C.a
=> 84
[147] pry(File):1>

What you want to do is this:

[17] pry(main)> class A
[17] pry(main)*   class << self
[17] pry(main)*     attr_accessor :a
[17] pry(main)*   end  
[17] pry(main)* end  
=> nil
[18] pry(main)> class B < A
[18] pry(main)*   class << self  
[18] pry(main)*     attr_accessor :a    
[18] pry(main)*   end  
[18] pry(main)* end  
=> nil
[19] pry(main)> class C < A
[19] pry(main)*   class << self  
[19] pry(main)*     attr_accessor :a    
[19] pry(main)*   end  
[19] pry(main)* end