Using extend

thing2.rb

module Logger
  def log str
    p str
  end  
end

class Thing2
  extend Logger
  
  log "this does work from class"   # => "this does work from class"
  
  def test_log
    begin
      log "this doesn't work from instance"
    rescue Exception => e
      p e                           
    end
    Thing2.log "this does work from class (via class in instance)"
  end
end

Thing2.new.test_log                 # => #<NoMethodError: undefined method `log' for #<Thing2:0x007fcb391016a0>>
                                    # => "this does work from class (via class in instance)"