Rails is a library, though, the advice applies to application/business code. Metaprogramming is extremely useful for making really simple-to-use libraries. I

Rails is a library, though, the advice applies to application/business code. Metaprogramming is extremely useful for making really simple-to-use libraries. If your business logic is full of metaprogramming, that's more of a problem, especially in this day of age where it's common for developers are only sticking around at any given job for 2 to 3 years.