How do I use the Enumerable mixin in my class?

I have a class called Note, which includes an instance variable called time_spent. I want to be able to do something like this:

current_user.notes.inject{|total_time_spent,note| total_time_spent + note.time_spent}

Is this possible by mixing in the Enumerable module? I know you are supposed to do add include Enumerable to the class and then define an each method, but should the each method be a class or instance method? What goes in the each method?

I'm using Ruby 1.9.2

It's easy, just include the Enumerable module and define an each instance method, which more often than not will just use some other class's each method. Here's a really simplified example:

class ATeam
  include Enumerable

  def initialize(*members)
    @members = members
  end

  def each(&block)
    @members.each do |member|
      block.call(member)
    end
    # or
    # @members.each(&block)
  end
end

ateam = ATeam.new("Face", "B.A. Barracus", "Murdoch", "Hannibal")
#use any Enumerable method from here on
p ateam.map(&:downcase)

For further info, I recommend the following article: Ruby Enumerable Magic: The Basics.

In the context of your question, if what you expose through an accessor already is a collection, you probably don't need to bother with including Enumerable.

The Enumerable documentations says the following:

> The Enumerable mixin provides collection classes with several > traversal and searching methods, and with the ability to sort. The > class must provide a method each, which yields successive members of > the collection. If Enumerable#max, #min, or #sort is used, the objects > in the collection must also implement a meaningful <=> operator, as > these methods rely on an ordering between members of the collection.

This means implementing each on the collection. If you're interested in using #max, #min or #sort you should implement <=> on its members.

See: Enumerable