[krig]

Well, the statement is circular, colloquial speech doesn't have to be coherent. It's my understanding of what people generally mean when they complain about UB in the C standard, and it seems to be what gingerbill means too.

My take on what he is saying is that the odin compiler won't try to exploit that there is some behavior which is platform-defined or only knowable at runtime to do aggressive optimizations etc.

https://xcancel.com/TheGingerBill/status/1495004577531367425

To point out that use after free is possible in Odin is not really a gotcha unless you really are just arguing semantics. That's by design, just like use after free is possible in C or C++ or Rust too.

[tialaramex]

> To point out that use after free is possible in Odin is not really a gotcha unless you really are just arguing semantics

In a language with UB, the use after free is UB. Which explains the nonsensical results.

If you're pretty sure this all makes sense, I recommend one tiny tweak to further unsettle you, change either (but not both) of the int types in my example to u8 instead. Now the use after free also results in type confusion - Odin has no idea this isn't the same type and so the machine code generated is for one type but the actual bits are for a different type with a different layout.

Bill's go-to is to blame somebody else, it's the operating system, or even the CPU which should define what happens and so it's not his fault. The thread you linked does this. But for type confusion those are Odin's types, nobody else can define how Odin works, the answer must come from Bill. What is supposed to happen here? Linux didn't define your programming language, Intel didn't define your programming language, this is your fault Bill.

[jibal]

Your understanding is completely wrong. UB means "undefined behavior" -- behavior that is not specified by the language standard or the implementation. UB being exploited by the compiler is a separate issue. Saying that there is no UB is saying that there's no undefined behavior; it is certainly not merely saying that the compiler doesn't exploit it.

I programmed in C for over 30 years and was a member of the C Standards Committee, which originated the language about undefined behavior ... I know what I'm talking about.

> To point out that use after free is possible in Odin is not really a gotcha unless you really are just arguing semantics. That's by design, just like use after free is possible in C or C++ or Rust too.

This completely misses the point and is a failure to understand at every level. Being able to use memory after being freed is not by design -- no one intends it, no one wants it. It's undefined behavior, and a program that does it is buggy. The reason that it's possible is because it's so hard to detect or prevent. To do so requires escape analysis, lifetime declarations, borrow checking, etc. etc. And no, use after free is not possible in Rust--not in safe code. It's hard to respond to that statement without being rude, so I will say no more.

[krig]

Well, first of all, I guess I am wrong! Hey, I'm not Bill, just a user of the language.

A couple of clarifications, though: I did mean unsafe rust, not the safe subset. No need to get rude!

Second of all, I am of course not under the illusion that Odin prevents use-after-free (and thus, technically, it does allow UB I guess). I just don't think Bill is either. So clearly he doesn't mean UB by the same definition as you do.

_My_ use of UB has always been in the context of what a compiler will do during optimization, and the discussion I've seen in the context of C compilers is that they perform optimizations that remove code or change code in surprising ways because the way the code was written technically resulted in UB. But I'm neither a spec writer or a compiler author, so I don't really care that much about the actual definition of the term.

Anyway, best of luck in convincing Bill to use the term correctly as well! I won't mention UB when talking about the benefits of Odin in the future. :)

[flysand7]

As someone who knows what they're talking about, I'm curious to hear from you, why you consider use-after-free an undefined behavior and not an unspecified behavior instead?

Because as far as I know both undefined behavior and unspecified behavior are the behaviors that aren't specified in the language standard nor the implementation. So what's the difference?