Eh. I absolutely get what you're saying. And this is for sure flying very close to the knife's edge. But if your assertion checks don't run in release mode, and due to some bug, those invariants don't hold, well, your program is already going to exhibit undefined behaviour. Why not let the compiler know about the undefined behaviour so it can optimize better?

The nice thing about this approach is that the assertion provides value both in debug and release mode. In debug mode, it checks your invariants. And in release mode, it makes your program smaller and faster.

Personally I quite like rust's choice to have a pair of assert functions: assert!() and debug_assert!(). The standard assert function still does its check in both debug and release mode. And honestly thats a fine default these days. Sure, it makes the binary slightly bigger and the program slightly slower, but on modern computers it usually doesn't matter. And when it does matter (like your assertion check is expensive), we have debug_assert instead.