Mixin both instance and class methods in Ruby

Question

I have a Ruby class into which I want to include both class and instance methods. Following the pattern described in "Ruby Pattern: Extend through Include", I'm currently using the following:

class SomeObject
 include SomeObject::Ability
 def self.some_builder_method(params)
 # use some_class_method ...
 end
end
module SomeObject::Ability
 module ClassMethods
 def some_class_method(param)
 # ...
 end
 end
 def self.included(klass)
 klass.extend(ClassMethods)
 end
 def some_instance_method
 # ...
 end
end

I'd rather not make two separate modules, one being included and the other being extended, because all the methods in my module logically fit together. On the other hand, this pattern requires me to:

1. Define an additional ClassMethods module.
2. Write a boilerplate self.included method for every module.

Is this the most idiomatic way to approach this?

• Flambino: AFAIK self.included + .extend(ClassMethods) is pretty much the way to do it. If you're using Rails, you can use ActiveSupport::Concern which handles this kind of thing.

Answer 1

You're doing it right :) It's a very common idiom, and widely accepted as the preferred way to handle this.

In case you're still in doubt, here are a few examples of the same pattern found in major projects out in the wild: sidekiq, mongoid and datamapper.