[12_throw_away]

No. An integer getting deterministically set to an unintended value is a bug. A bug is not the same thing as UB. (Even if it were non-deterministic, it would still not be anything like UB.) It's not the same ballpark, not even the same sport.

[jstimpfle]

What if the wrapped index is used to construct an invalid pointer? It might be possible, not sure. What if the integer is used to read the wrong data from disk, or corrupt data on disk by writing to the wrong location?

[12_throw_away]

> What if the wrapped index is used to construct an invalid pointer?

Constructing an invalid pointer in rust is UB, yes, but integer wraparound is not.

> What if the integer is used to read the wrong data to a disk, or corrupt data on disk by writing to the wrong location?

Then it is a very bad bug.

> What if the program controls a nuclear power plant and the integer causes the control system to fail, causing memory errors due to radiation from the meltdown?

Then it is a very very bad bug.

> What if the wrapped integer causes the program to output the true name of god, and the programmer, in their last minutes of existence, looks up to see, overhead, without any fuss, the stars going out?

Ok, you got me, this one is UB.

[kobebrookskC3]

> Constructing an invalid pointer in rust is UB

no, it is dereferencing, not constructing, an invalid pointer, that is UB. there is even a safe function provided to construct an invalid but non-null pointer: `https://doc.rust-lang.org/stable/std/ptr/fn.dangling.html`

[12_throw_away]

you're of course 100% right, I was so proud of my nerd joke that I got like the most basic rust safety rule wrong :(

[steveklabnik]

> What if the wrapped index is used to construct an invalid pointer?

Using that pointer would be UB, but that is UB, not the addition.

> What if the integer is used to read the wrong data from disk, or corrupt data on disk by writing to the wrong location?

That is a bug, but it is not undefined behavior.