class_inheritable_attribute.rb

# Adds class inheritable attributes to every class. See the examples for more information.
# Originally posted on http://pastie.org/39201 (9 February 2007)
# 

require 'active_support'

class Class
  def class_inheritable_attributes(*syms, &block)
    eigenclass = class << self; self; end
    syms.each do |sym|
      eigenclass.send :define_method, sym do |*values|
        if value = values.first
          value = block.call value if block
          write_inheritable_attribute sym, value
        else
          read_inheritable_attribute sym
        end
      end
      class_eval <<-EOS
        def #{sym}
          self.class.read_inheritable_attribute :#{sym}
        end
      EOS
    end
  end

  alias :class_inheritable_attribute :class_inheritable_attributes
end

EXAMPLES.txt

class Base
  class_inheritable_attribute(:root) { |root| Pathname.new(root).realpath }
end

class A < Base
  root '.'
end

>> Base.root
=> nil
>> a = A.new
=> #<A:0xb78a2c64>
>> a.root
=> #<Pathname:/home/vjt/code/ecole/lib>
>> A.root
=> #<Pathname:/home/vjt/code/ecole/lib>
>> A.root '.'
=> #<Pathname:/home/vjt/code/ecole/lib>
>> A.root '..'
=> #<Pathname:/home/vjt/code/ecole>

# - vjt@openssl.it