dummy.rb

require 'stopwatch'

class Dummy
  extend MethodDecorators 

  +Stopwatch
  def test
    sleep(0.1)
  end

  +Stopwatch.new("custom name")
  def test2
    sleep(0.2)
  end

  +Stopwatch
  def test_with_block(&blk)
    blk.call
  end
end

#Examples
Dummy.new.test                            #outputs 'Dummy.test, Elapsed...'
Dummy.new.test2                           #outputs 'custom name, Elapsed...'
Dummy.new.test_with_block { sleep(0.3) }  #outputs 'Dummy.test_with_block, Elapsed...'

Stopwatch.time("Block instrumentation") { sleep(0.4) } #outputs 'Block instrumentation, Elapsed...'
Stopwatch.time { sleep(0.5) }             #outputs 'Elapsed...'

stopwatch.rb

require 'method_decorators'

class Stopwatch < MethodDecorator
  def initialize(name=nil)
    @name = name
  end

  def call(original, this, *args, &blk)
    time(original) { original.call(*args, &blk) }
  end

  def self.time(name=nil, &block)
    Stopwatch.new(name).time { block.call }
  end

  def time(method=nil, &blk)
    start = Time.now
    begin
      blk.call
    ensure
      if @name 
        message = "#{@name}, "
      else
        message = case method
        when Method then "#{method.owner}.#{method.name}, "
        when nil then ""
        else "#{method}, "
        end
      end

      puts "#{message}Elapsed: #{Time.now - start}s"
    end
  end
end