memoize

require 'activesupport'

class Module
  def memoize method
    define_method :"#{method}_with_memoization" do |*args|
      varname = "@_memoized_#{method}"
      if instance_variable_names.include?(varname)
        instance_variable_get(varname)
      else
        instance_variable_set(varname, send("#{method}_without_memoization"))
      end
    end
    alias_method_chain method, :memoization
  end
end

class Foo
  def bar
    rand(1000)
  end

  memoize :bar
end


f = Foo.new
p [f.bar, f.bar]