No, the problem is that std::vector still calls the constructor and destructor of each and every object in the array at least once. This is a performance loss i

No, the problem is that std::vector still calls the constructor and destructor of each and every object in the array at least once. This is a performance loss if they don't do anything - you have to rely on the compiler to inline the call, then remove the code. For POD datastructures it can be significant, because those are usually the largest arrays in your application. This is why e.g. Facebook's Folly library detects POD types in their vector and doesn't call ctors and dtors at all. Similarly, std::vector has to allocate more memory every time it has to grow and copy all its contents, whereas for POD datatypes you can just use realloc which can save copies. These are all borderline microoptimisations, but they matter for realtime highly responsive software. Or just in general when you need to squeeze out every last bit of performance.