caceable.rb

module Cacheable

  def self.extended(base)
    @@unaliased_methods = {}
    @@cacheable_methods = Module.new
  end

  def method_added(m)
    if @@unaliased_methods[m]
      cache_method(m)
      @@unaliased_methods[m] = false

      if @@unaliased_methods.values.none?
        prepend_cached_methods
      end
    end
  end

  ## uncommenting the commented lines here allows a subclass to cache
  ## methods from a parent class, but this leads to unexpected results
  ## when trying to override the method.
  ##
  ## As it's written here, the `caches` line must come before the methods
  ## are defined
  def caches(*method_names)
#    prepend_now = true

    method_names.each do |m|
#      if instance_methods.include?(m)
#        cache_method(m)
#      else
        @@unaliased_methods[m] = true
#        prepend_now = false
#      end
    end

#    prepend_cached_methods if prepend_now
  end

  private

  def cache_method(name)
    self.send(:alias_method, "#{name}_uncached", name)

    @@cacheable_methods.send(:define_method, name) do |*args|
      # puts "I am the cached version of #{name}"
      @cached_result ||= self.send("#{name}_uncached", *args)
    end
  end

  def prepend_cached_methods
    self.prepend(@@cacheable_methods)
  end
end

class Animal
  extend Cacheable
  caches :long_running_method

  attr_accessor :name, :age

  def initialize(name, age=42)
    @name = name
    @age = age
  end

  def greeting
    "I am #{name} and I am #{long_running_method} years old."
  end

  def long_running_method
    puts "in long running method..."
    sleep 5
    @age
  end
end

class Dog < Animal
  extend Cacheable  # not really needed, but for isolation

  caches :greeting

  def greeting
    sleep 3
    "this is a different greeting"
  end
end

animal = Animal.new("Human")
puts animal.greeting
puts animal.greeting

dog = Dog.new("Rufus", 6)
puts dog.greeting
puts dog.greeting