Just saying that it's defined and then not saying what the definition is, is no different from saying it's undefined.
> Just saying that it's defined and then not saying what the definition is, is no different from saying it's undefined.
It actually is, because, as I said earlier, “undefined behavior” is a term of art with very specific meaning. Regardless, it is defined: there are two possible behaviors, with one guaranteed with that flag and the other chosen by implementations.
Now are there many cases of UB in C, many more than strictly need to exist on contemporary platforms? For sure there are. But does it affect me? Not unless I need a specific behaviour common to most contemporary platforms that I can't get within the confines of C, even considering compiler specific extensions. Honestly I can't come up with any of the top of my head. Maybe some integer-shifting stuff or such, if the compiler was able to prove I'm doing sth undefined, it can leave out that code (or delete my mail, for the doomers). Personally, it hasn't happened to me, and it's on the compiler authors to not do stupid things too.
Leaving all the semantic hair-splitting aside. What is the practical difference in how you write a Rust program compared to a C program, given that integer overflow is "defined" in Rust?
This is an example of a compiler flag that adds definition to undefined behavior, which is of course, legal to do. That doesn't change that in the standard, it is undefined behavior, and in Rust, it is not.
> To say that overflow would be defined in Rust is at least half a lie.
In the context of "undefined behavior", it is not a lie at all.
> So the user has to constrain the set of valid inputs, and do manual sanitization, just like in C.
No, because the consequences of how the two languages define these behaviors are very, very different.