memoize.rb

memoize.rb

module Memoize
  def memoize(name)
    m = Module.new do
      define_method name do |*args|
        return instance_variable_get("@_#{name}") if instance_variable_defined? "@_#{name}"
        
        instance_variable_set("@_#{name}", super(*args))
      end
    end
    
    prepend m
  end
end

class Foo
  extend Memoize
  
  memoize def foo
    puts 'hi'
    
    5
  end
end

f = Foo.new

f.foo
# hi
#=> 5

f.foo
#=> 5