method_added example 2

memoizer.rb

class Memoizer
  def self.memoize
    @memoized = true
  end    

  def self.method_added(method_name)    
    if @memoized
      # We're disabling memoization so that when we call "define_method",
      # we're not going to loop indefinitely
      @memoized = false

      # 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
  end

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

### When defining the class, this is the output:
#
# :run

### When using an instance, this is the output:
#
# > t = Memoizer.new
# => #<Memoizer:0x007fa2ce852c58>
#
# > t.run
# Computing value
# => 2
#
# > t.run
# Returning cached valued
# => 2
#
# Note that there was 3 seconds of pause between line 54 and 55,
# while there was none between line 58 and 59.