Comment by madsohm

Since using `def` to create a method returns a symbol with the method name, you can do something like this too:

  memoize def expensive_calculation(arg)
    @calculation_count += 1
    arg * 2
  end, ttl: 10, max_size: 2

  memoize def nil_returning_method
    @calculation_count += 1
    nil
  end