Timothy Lochner

Why would const change the type? Wouldn't that make any const_cast UB?

It seems to me that the two vector types are unrelated. So they may as well be struct A{}; and struct B{}; It seems that you may as well be doing: A a; B& b = (b&)a; which I believe is UB.

Why do you think that? Nothing in the vector itself changes (ptr + size) and the type pointed to also doesn't change. Just the access semantics. Afaik. I can const_cast a const int and modify it without it being UB. Right?

The compiler is free to reorder members within a class regardless of the order they were declared in. No implementations do (that I know of), but we aren't asking about implementations.

I guess, all that being said, I gave it a shot in godbolt with -fsanitize=undefined and it didn't return any errors. *shrug*. If it were me, I'd use a span<int const *>.

At risk of inciting a mob, those who follow @lefticus may be best equipped to answer this.

Yes, they are two completely unrelated types, and it is UB. Breaks strong aliasing rules. Most uses of const_cast enable UB and almost all uses of reinterpret_cast result in UB, and your c-style cast is a reinterpret_cast. I'll let @shafikyaghmour link his articles

So what's the most performant way to get a const version of those pointers in an array format? Std::span? And before c++20?