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Memory Safety is a Red Herring
(steveklabnik.com)
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this post was submitted on 24 Dec 2023
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Rust
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I don't understand this fixation with undefined behavior. Its origins are in the design decision of leaving the door open for implementations to employ whatever optimization techniques they see fit without the specification get in the way. This is hardly a problem.
In practical terms, developers are mindful to not rely on those traits because as far as specifications go they have unpredictable implications, but even so they are never a problem. I mean, even in C and C++ it's trivial to tweak the compiler to flag undefined behavior as warnings/errors.
Sometimes it sounds like detractors just parrot undefined behavior as some kind of gotcha in ways I'm not even sure they fully understand.
What problem do you think that undefined behavior poses?
I'm just a noob when it comes to low level languages, having only been in C# and python. But I took a course on C++ and encountered something that didn't seem right. And I asked and got the "that's undefined behavior". And that didn't quite sit tight with me. We don't know what will happen? It'll probably crash? Or worse? How can one not know how a programming language will perform? I felt it was wrong.
Now, it's quite some time since that happened, and I understand why it's undefined. But I still do not think it should be allowed by default. C and C++ both are "free to do as you want" languages, but I don't think a language should let you do something that's undefined especially if you aren't aware you're doing it. Everyone makes mistakes, even stupid ones. If we can make a place where undefined behavior simply won't happen, why not go there? If you need some special tricks, you can always drop the guard where you need it. I guess I'm just reiterating the article here though. But that's the point for me, if something can enforce "defined behavior" by default then I'd want that.
If you really want to know you can. Basically in most cases it depends on the compiler. Sometimes the hardware. The point is that you should not expect any specific behavior because the standard doesn't specify one
The standard differentiates between "unspecified" behavior, which is as you describe, and "undefined" behavior, which may be completely nondeterministic at runtime.