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Dioxus Labs + “High-level Rust
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this post was submitted on 24 Jun 2024
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Unwrap comes up all the time in the standard library.
For example, if you know you're popping from a non-empty vector, unwrap is totally the right too for the job. There are tons of circumstances where you know at higher levels that edge cases defended against at lower levels with
Optioncannot occur.(DISCLAIMER: I haven't read the post yet.)
That would/should be
.expect(). You register your assumption once, at the source level, and at the panic level if the assumption ever gets broken. And it's not necessarily a (local) logical error that may cause this. It could be a logical error somewhere else, or a broken running environment where sound logic is broken by hardware or external system issues.If you would be writing comments around your
.unwrap()s anyway (which you should be), then.expect()is a strictly superior choice.One could say
.unwrap()was a mistake. It's not even that short of a shortcut (typing wise). And the maximumly lazy could have always written.expect("")instead anyway.I personally think that unwrap and the question mark operator were a mistake.
Fair. But unwrap versus expect isn't really the point. Sure one has a better error message printed to your backtrace. But IMO that's not what I'm looking for when I'm looking at a backtrace. I don't mind plain unwraps or assertions without messages.
From my experience, when people say "don't unwrap in production code" they really mean "don't call panic! in production code." And that's a bad take.
Annotating unreachable branches with a panic is the right thing to do; mucking up your interfaces to propagate errors that can't actually happen is the wrong thing to do.
You're assuming the PoV of a developer in an at least partially controlled environment.
Don't underestimate the power of (preferably specific/unique) text. Text a user (who is more likely to be experiencing a partially broken environment) can put in a search engine after copying it or memorizing it. The backtrace itself at this point is maybe gone because the user didn't care, or couldn't copy it anyway.
What should be a non-absolutest mantra can be bad if applied absolutely. Yes.
What should be a non-absolutest mantra can be bad if applied absolutely.
You talk about "non-absolutist," but this thread got started because the parent comment said "literally never."
I am literally making the point that the absolutist take is bad, and that there are good reasons to call unwrap in prod code.
smdh
Don't get angry with me my friend. We are more in agreement than not re panics (not
.unwrap(), another comment coming).Maybe I'm wrong, but I understood 'literally' in 'literally never' in the way young people use it, which doesn't really mean 'literally', and is just used to convey exaggeration.
No, I actually meant it as in the traditional meaning of literally. As in
along with a pre-commit hook that does
cargo clippy -D warnings(deny warnings).
There are always better ways to write an unwrap, usually via pattern matching and handling the error cases properly, at the very least logging them.
As a sysadmin I have sadly encountered too many situations where a programmer thought "oh, this will never happen" to agree with you that a code construct that provides no information to the user should be used in such cases.