Oh, on the contrary, the separate structure is needed and useful because it offers _less_, not more:

* APIs/function signatures explain more clearly what are the intended uses of the structure that's passed.

* More potential for compiler optimization

* Some potential for having these on the stack (if the compiler deduces the size already at compile-time)

* More convenient for static analysis

* No plethora of confusing constructors (including the infernal two-element ctors which can be misinterpreted super-easily)

etc.

The reason I'd want "frozen-size vector" is to replace pairs of data members of the form `T* foos; size_t foos_len;` without paying another 8 bytes to store a useless capacity that's never going to change.

But I don't think that makes such a container worth adding to the STL. So far, it hasn't even been worth writing in our own code. But that's the reason I've thought about writing it.