Problem is, you call pop on empty vector in C++, you get nasal demons. Not a case in Rust.

I'm not a C++ expert but here is my understanding. Vector is essentially a tuple of (dynamic_array_address: ptr, size: size_t, capacity: size_t). To pop a value from vector you just decrements size. So what happens when you have empty vec? Your size is 0, and you're substracing 1, which causes undefined behavior.

Correct way is to check BEFORE you pop_back().

In Rust, any number of invocation of pop() will not result in undefined behavior. You can ignore the value, or you can check it, but it doesn't expose you to UB just for slightly misusing a vector.