Because alternative makes it not much better or safer. It could throw an exception when vector is empty (or return an error in whatever other way) - you will ca

Because alternative makes it not much better or safer. It could throw an exception when vector is empty (or return an error in whatever other way) - you will catch the exception and then do what, try to pop_back() again or what exactly can you do? You are at very bad odds to continue with the program when such a fundamental issue pops up in your program so I guess you can only terminate the process? There is no generally meaningful way to recover from an error condition like this, which in its nature is a logical mistake in your code. And that's the reason why I think std::vector won't throw an exception but will give you an opt-in to terminate the process through the assert. I think it's not about the performance, although it can be argued, but it's more fundamental code design problem.