ClassAttr

Adds #class_attr_accessor (and reader/writer) and #inheritable_class_attr_accessor (and reader/writer of course) to Class.

class Polygon
  class_attr_accessor :sides
end

Polygon.sides = 5
Polygon.sides #=> 5

class Square < Polygon
end

Square.sides #=> nil


class InheritablePolygon
  inheritable_class_attr_accessor :sides
end

Polygon.sides = 4

class NewSquare < Polygon
end

Square.sides #=> 4

You can provide default values using a hash with :default set for the last value, or if just creating one accessor/reader/writer add => defaultvalue to the end, this example should make it more clear:

class Person
  class_attr_accessor :name => 'John Doe'
  inheritable_class_attr_accessor :arms, :legs, :default => 2
  inheritable_class_attr_accessor :fingers, :toes, :default => 5
end

class Agent < Person
  @name = "James Bond"
end  

Person.name #=> "John Doe"
Person.arms #=> 2
Person.toes #=> 5
Agent.name  #=> "James Bond"
Agent.legs  #=> 2

Install

(sudo) gem install class_attr

Use

require 'class_attr'

Or, as in some cases this may be overkill, copy the parts you need over (you will need to modify it, but that should be easy to work out.)

Important!

If in a class you define the self.inherited method, make sure to call super at the end (or beginning) otherwise default values will not be set for the subclass. But I'm guessing you already called super anyway in a method like that.

Thanks

• http://railstips.org/blog/archives/2006/11/18/class-and-instance-variables-in-ruby/ For originally demystifying the class instance variable thing.
• http://www.raulparolari.com/Rails/class_inheritable For ideas on how to implement class level attribute accessors which inherit values.

Copyright

Copyright (c) 2010 Joshua Hawxwell. See LICENSE for details.