Rust

5744 readers

7 users here now

Welcome to the Rust community! This is a place to discuss about the Rust programming language.

Wormhole

[email protected]

Credits

The icon is a modified version of the official rust logo (changing the colors to a gradient and black background)

founded 1 year ago

MODERATORS

[email protected]

Dioxus Labs + “High-level Rust (dioxus.notion.site)

submitted 2 months ago by [email protected] to c/[email protected]

18 comments fedilink hide all child comments

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 3 points 2 months ago (2 children)

Unwrap should literally never appear in production code

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 Option cannot occur.

[–] [email protected] 5 points 2 months ago* (last edited 2 months ago) (2 children)

(DISCLAIMER: I haven't read the post yet.)

For example, if you know you’re popping from a non-empty vector, unwrap is totally the right too(l) for the job.

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.

[–] [email protected] 0 points 2 months ago

I personally think that unwrap and the question mark operator were a mistake.

[–] [email protected] -1 points 2 months ago (2 children)

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.

[–] [email protected] 3 points 2 months ago

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.

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.

[–] [email protected] 0 points 2 months ago (1 children)

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.

What should be a non-absolutest mantra can be bad if applied absolutely. Yes.

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.

What should be a non-absolutest mantra can be bad if applied absolutely.

[–] [email protected] 1 points 2 months ago (1 children)

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

[–] [email protected] -1 points 2 months ago (1 children)

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.

[–] taladar 2 points 2 months ago

No, I actually meant it as in the traditional meaning of literally. As in

[lints.clippy]
unwrap_used = "warn"
expect_used = "warn"

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.

[–] taladar 1 points 2 months ago

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.