[YZF]

But sometimes you should copy and paste code because those difference pieces of code can evolve independently. Knowing when to do this and when not to do this is what we do and no rule can blindly say one way or the other.

Even the most obvious of functions like sin() and cos() may in some circumstances warrant a specialized implementation. Sure, for most stuff you should not have 10 copies of those all over the place. But sometimes you might.

DRY is a bad rule. The more appropriate rule is avoid duplicating code when not doing so results something better. I.e. judgement always trumps rules.

[Pannoniae]

Oh yeah, 100% this, I made a homemade sincos implementation which roughly returns the right result roughly all the time. It's nice because I don't care about the exact answer (it's for randomly rotating angles for generating caves, terrain generation) and it's like 5x as fast as doing it properly!