solutions.rb

module Interactors
  class Base
  end

  class ImportantThing < Base
    @@increment = 0

    def initialize(*args) 
      # .... some setup
      #
    end
    
    def call(*args)
      @@increment += 1
      return "time is #{@@increment}"
    end
  end
  
  module Memoize
    def call(*args)
      @memory ||= super
    end
  end
end


i = Interactors::ImportantThing.new().extend(Interactors::Memoize)
a = Interactors::ImportantThing.new()

puts 'memoized'
puts i.call()
puts i.call()
puts i.call()
puts i.call()

puts 'non-memoized'
puts a.call()
puts a.call()