To the point of complexity, the allocation makes the container unfit for over-aligned types. But honestly I don't even know if STL containers are over-alignment

To the point of complexity, the allocation makes the container unfit for over-aligned types. But honestly I don't even know if STL containers are over-alignment aware. So instead of (T*)malloc(sizeof(T) * capacity_); it should be something like this if you want to deal with over-aligned types. (T*) operator new(sizeof(T)*capacity_, std::align_val_t{alignof(T)}); Also, in the reallocation function the elements are move-assigned to uninitialized memory. They should be move-constructed with a placement-new. And of course calling the destructors of the moved-from objects is still required. It's of course a little telling that the compiler will not complain about these errors and you have to use and know to use tools like address sanitizer, memory sanatizer and valgrind to let a machine help you find them.