How can Ruby's attr_accessor produce class variables or class instance variables instead of instance variables?

Question

If I have a class with an attr_accessor, it defaults to creating an instance variable along with the corresponding getters and setters. But instead of creating an instance variable, is there a way to get it to create a class variable or a class instance variable instead?

Answer 1

Like this:

class TYourClass   class << self     attr_accessor :class_instance_variable   end end 

You can look at this as opening the metaclass of the class (of which the class itself is an instance) and adding an attribute to it.

attr_accessor is a method of class Class, it adds two methods to the class, one which reads the instance variable, and other that sets it. Here's a possible implementation:

class Class   def my_attr_accessor(name)     define_method name do       instance_variable_get "@#{name}"     end      define_method "#{name}=" do |new_val|       instance_variable_set "@#{name}", new_val     end   end end 

Completely untested class attribute accessor:

class Class   def class_attr_accessor(name)     define_method name do       class_variable_get "@@#{name}"     end      define_method "#{name}=" do |new_val|       class_variable_set "@@#{name}", new_val     end   end end