Ruby Memoize

memo.rb

module Memoize
  module DefMemo
    def defmemo(name, &block)
      define_method(name) do |*args|
        __memo__[name].fetch(args) do |key|
          __memo__[name][key] = instance_exec(*args, &block)
        end
      end
    end
  end

  def __memo__
    @__memo__ ||= Hash.new { |h, k| h[k] = {} }
  end

  def self.included(klass)
    klass.extend(DefMemo)
  end
end

class Foo
  include Memoize

  attr_accessor :var
  attr_accessor :truthy

  defmemo :bar do |x|
    var + x
  end

  defmemo :get do
    truthy
  end
end

foo = Foo.new

foo.var = 1
puts foo.bar(1) == 2
foo.var = 5
puts foo.bar(1) == 2
puts foo.bar(2) == 7

foo.truthy = false
puts foo.get == false

foo.truthy = true
puts foo.get == false