Example without decorators

memoizer2.rb

class Memoizer
  def self.memoize(method_name)
    # Getting the method as an object
    target_method = instance_method(method_name)

    # Overriding it !
    define_method(method_name) do |*args, &blk|
      # Initializing the cache object
      @_memoize_storage ||= {}

      if @_memoize_storage[method_name]
        # Cached? Do not compute !
        puts "Returning cached valued"
      else
        # Not cached? compute and store the result !
        puts "Computing value"
        decorated = target_method.bind(self)

        @_memoize_storage[method_name] = decorated.call(*args, &blk)
      end

      # Return the cached result
      @_memoize_storage[method_name]
    end
  end

  memoize def run
    sleep(3)
    1 + 1
  end
end