Comment by steveklabnik | Hacker News Reader

Comment by steveklabnik | Hacker News Reader

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? is explicitly a replacement for try!, yes.

> functions that have to return a single type

Well, all functions have to return a single type, though that type may be a composite type, like a tuple.

Less pedantically, `?` lets you (well, will let you) unwrap values and convert their error cases between each other. So once the next round of stabilization happens, if you have a function that returns Results, you can mix ? on Options and Results in the body, and vice versa. And it can be extended for other types too. Basically, it's an early return "protocol" if you will.

By single type, I meant to hint not being able to mix ? on Options and Results in the body, but good to know that's soon possible! Though you still can't, eg, use `?` in main()

That's coming as well!

Interesting. Looking at the proposal it seems specific to main() and not any void returning function, by automatically picking an exit status. I suppose I worry the construct has a lack of control (log diagnostics, exit status, cleaning, etc) when bailing and can’t handle eg continue, break too.

exit status and cleaning should be just fine, logging or something else would need to not do it, yeah. continue and break would be weird outside of loops.

Also regarding an "early return protocol", I'd also be curious for continue, break, any ! type expression. For one of the Rust projects I worked on, I wrote an unwrap macro on Option that takes a secondary ! argument.

Tracking issue for using it in main: https://github.com/rust-lang/rust/issues/43301

You can mix them if you take your Options and convert them into Results with the Option::ok_or(E) method.

    do_this(x).ok_or(CustomError::ThisError)?;

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