[steveklabnik]

Basically, overflow doesn't lead to memory safety in isolation. That's the key of it. The worst that can happen is a logic errors, and we are not trying to stop all of those with the compiler :) Justifying a 20%-100% speed hit (that was cited in the thread) for every integer operation to save something that can't introduce memory safety is a cost we can't afford to pay.

If you want the full details, https://github.com/rust-lang/rfcs/blob/1f5d3a9512ba08390a222... is the RFC, and https://github.com/rust-lang/rfcs/pull/560 was the associated discussion, there is a lot of it.

EDIT: oh, one more thing that may have significance you may or may not have picked up: one reason why under/overflow in C and C++ is dangerous is that certain kinds are undefined behavior. It's well-defined in Rust. Just doing that alone helps, since the optimizer isn't gonna run off and do something unexpected.