Ruby 2.1 method injection POC

gistfile1.rb

module Instrumenter

  def instrument(method)
    alias_method "_#{method}", method
    define_method method do
      start = Time.now
      result = send("_#{method}")
      puts "Elapsed: #{Time.now - start}"
      result
    end
  end

end

class Calculator

  extend Instrumenter

  instrument def calculate
    sleep 1
    1 + 1
  end

end

i = Calculator.new
puts i.calculate