composed_cache.rb

class ComposedCache
  def initialize(target)
    @target  = target
  end

  def cache(*method_names)
    method_names.each do |m|
      original = @target.method(m)
      results  = {}

      @target.define_singleton_method(m) do |*a|
        results[[m, a]] ||= original.call(*a)
      end
    end
  end

  def method_missing(m, *a, &b)
    @target.send(m, *a, &b)
  end
end

class Numbers
  def fib(n)
    raise ArgumentError if n < 0
    return n if n < 2

    fib(n - 1) + fib(n - 2)
  end
end

n = ComposedCache.new(Numbers.new)
n.cache(:fib)
  

(0..100).each { |e| p [e, n.fib(e)] }