memoize.rb

class Method
    def memoize!(time = nil)
        name = self.name
        owner = self.owner
        method = self.to_proc
        self.unbind
        owner.send(:define_method, name) do |*args, &block|
            @results ||= {}
            if !@time || (time && @time + time < Time.now)
                result = method.call(*args, &block)
                @time = Time.now
                @results[[args, block]] = result
            end
            @results[[args, block]]
        end
        owner.method(name)
    end
end