The CXX Debate

steveklabnik.com

7 pointssteveklabnik4 comments

"we know that we can pass any u32 to this function, and it's safe"

What happens if you pass in 0xFFFFFFFF?

This is a great point; I was thinking purely of Rust's semantics, where this is safe, and ends up turning into a panic or a zero. I'll add something here, thank you.

EDIT: wait, since this is unsigned, it is the same semantics as Rust. Well, it wraps no matter the optimization level, but it's not UB.

I haven't quite wrapped my head around Rust but I know that anything that moves the possibility of UB towards 0 is a godsend. Just ask the folks at ESA who worked on the first Ariane 5 launch.

Rust's semantics are:

* in debug builds, you get a panic on overflow

* otherwise, you may choose to panic, but if you do not, it is two's compliment wrapping

It is defined this way so that someday if checks get cheap enough we can enable them in release builds too, but at least it's not UB!

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