Ruby memoization exercise

memoization.rb

require 'minitest/autorun'

module Memoization
  def memoize(f, injected_cache={})
    m = instance_method(f)
    define_method(f) do |*args|
      cache = injected_cache.clone
      define_singleton_method(f) do |*args|
        unless cache[args]
          puts "Actually calculating..."
          cache[args] = m.bind(self).call(*args)
        end
        cache[args]
      end
      send(f, *args)
    end
  end
end

class Bar
  extend Memoization
  def initialize(x)
    @x = x
  end
  def inc
    @x + 1
  end
  memoize :inc
end

describe Memoization do
  # it "works" do
  #   f = Foo.new
  #   f.inc(123).must_equal 124
  #   f.inc(123).must_equal 124

  #   f.inc(0).must_equal 1
  #   f.inc(0).must_equal 1

  #   f.sum(1,2).must_equal 3
  #   f.sum(1,2).must_equal 3

  #   f.sum(100, 200).must_equal 300
  #   f.sum(100, 200).must_equal 300
  # end

  it "foo" do
    cache = MiniTest::Mock.new
    Foo = Class.new do
      extend Memoization
      def inc(x)
        x + 1
      end
      memoize :inc, cache
    end
    f = Foo.new
    cache.expect(:clone, cache, [])
    cache.expect(:[]=, nil, [0])
    cache.expect(:[], 
    f.inc(0)
  end

  it "makes separate caches per object" do
    b1 = Bar.new(0)
    b1.inc.must_equal(1)
    b1.inc.must_equal(1)

    b2 = Bar.new(0)
    b2.inc.must_equal(1)
    b2.inc.must_equal(1)
  end
end