Question

I’m working on a module that, among other things, will add some generic ‘finder’ type functionality to the class you mix it into. The problem: for reasons of convenience and aesthetics, I want to include some functionality outside the class, in the same scope as the class itself.

For example:

class User
  include MyMagicMixin
end

# Should automagically enable:

User.name('Bob')   # Returns first user named Bob
Users.name('Bob')  # Returns ALL users named Bob 
User(5)            # Returns the user with an ID of 5
Users              # Returns all users

I can do the functionality within these methods, no problem. And case 1 (User.name('Bob')) is easy. Cases 2–4, however, require being able to create new classes and methods outside User. The Module.included method gives me access to the class, but not to its containing scope. There is no simple “parent” type method that I can see on Class nor Module. (For namespace, I mean, not superclass nor nested modules.)

The best way I can think to do this is with some string parsing on the class’s #name to break out its namespace, and then turn the string back into a constant. But that seems clumsy, and given that this is Ruby, I feel like there should be a more elegant way.

Does anyone have ideas? Or am I just being too clever for my own good?

Answer 1

In your example, User is just a constant that points to a Class object. You can easily create another constant pointer when MyMagicMixin is included:

module MyMagicMixin
  class <<self
    def self.included(klass)
      base.extend MyMagicMixin::ClassMethods
      create_pluralized_alias(klass)
    end

    private

    def create_pluralized_alias(klass)
      fq_name = klass.to_s
      class_name = fq_name.demodulize
      including_module = fq_name.sub(Regexp.new("::#{class_name}$", ''))
      including_module = including_module.blank? ? Object : including_module.constantize
      including_module.const_set class_name.pluralize, klass
    end
  end

  module ClassMethods
    # cass methods here
  end
end

Of course this doesn’t answer whether you should do such a thing.