Programming Ruby 3.3

Modules and Mixins

As we saw in ​Mixins​, when you include a module into a Ruby class, the instance methods in that module become available as instance methods of the class, like this:

module Logger
  def log(msg)
    STDERR.puts Time.now.strftime("%H:%M:%S: ") + "#{self} (#{msg})"
  end
end

class Song
  include Logger
end

s = Song.new
s.log("created")

Produces:

17:16:19: #<Song:0x0000000104717708> (created)

Ruby implements include very simply. The module you include is added as an ancestor of the class being defined. It’s as if the module is the parent of the class that it’s mixed into. And that would be the end of the description except for one small wrinkle. Because the module is injected ...