include and extend using included

include.rb

module Log
  def Log.included cls
    cls.extend Log #also works by passing self, but Log is less confusing
  end
  def log str
    p str
  end  
end

class Thing
  include Log
  
  log "works from class"  # => "works from class"
  
  def test_log
    log "works from instance"
    self.log "works from self (in instance)"
    Thing.log "works from class (in instance)"
  end
end

Thing.new.test_log        # => "works from instance"
                          # => "works from self (in instance)"
                          # => "works from class (in instance)"