That is not the same thing at all. Unreachable means that entire branch cannot be taken and the compiler is free to inject optimizations assuming that’s the case. It doesn’t need to crash if the violation isn’t met - indeed it probably won’t. It’s the equivalent of having something like

    x->foo();
    if (x == null) {
        Return error…;
    }

This literally caused a security vulnerability in the Linux kernel because it’s UB to dereference null (even in the kernel where engineers assumed it had well defined semantics) and it elided the null pointer check which then created a vulnerability.

I would say that using unreachable() in mission critical software is super dangerous, moreso than an allocation failing. You want to remove all potential for UB (ie safe rust with no or minimal unsafe, not sprinkling in UB as a form of documentation).

C++ keeps getting bigger and bigger :D

Thanks for sharing