inheritable_instance

InheritableInstance

Allow descending classes to inherit instance variables. This is useful for persisting class-level configuration.

Installation

Add this line to your application's Gemfile:

gem 'inheritable_instance'

Usage

Insert the InheritableInstance module into the ancestry chain of your class:

class FakeClass
  extend InheritableInstance
end

Then use inheritable_instance to set any instance variables that you want to be inherited by subclasses:

class FakeClass
  inheritable_instance :@thing_one, 1
  inheritable_instance :@thing_two, 2
end

These variables will be automatically set on inheritance:

class DoubleFake < FakeClass; end
DoubleFake.instance_variable_get(:@thing_one) == 1
DoubleFake.instance_variable_get(:@thing_two) == 2

It is convenient to pair this with the attr_* methods:

class << FakeClass
  attr_accessor :thing_two
end
DoubleFake.thing_two = "two"
FakeClass.thing_two == 2
DoubleFake.thing_two == "two"

Note that the values are duplicated (when possible):

class OneTwoThree
  extend InheritableInstance
  inheritable_instance :@list, []
  class << self; attr_reader :list; end
end
OneTwoThree.list << 1 << 2 << 3
Abc = Class.new(OneTwoThree)
Abc.list << 'a' << 'b' << 'c'
Abc.list == [1,2,3,'a','b','c']
OneTwoThree.list == [1,2,3]

Additional Details

If for some reason it is inconvenient to extend the module, there is an Includible helper that you can use instead:

class SameAsFakeClass
  include InheritableInstance::Includible
end

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/fledman/inheritable_instance.

License

The gem is available as open source under the terms of the MIT License.