Is `dyn_array` the same as `vector` or the proposed `dynarray`?

No. dyn_array is a container, like vector, but it is not resizable; its size is fixed at runtime when it is constructed. It is a safe way to refer to a dynamically "heap"-allocated fixed-size array. Unlike vector, it is intended to replace array-new[]. Unlike the dynarray that has been proposed in the committee, this does not anticipate compiler/language magic to somehow allocate it on the stack when it is a member of an object that is allocated on the stack; it simply refers to a "dynamic" or heap-based array.