Confused by lifetime error messages? Tell me about it!

[sinistersnare]

Shouldnt this thread be in users?

[steveklabnik]

Nowadays, it would be. It was created before users existed. And since they’re separate instances, moving them isn’t easy.

[kornel]

[I haven’t found the corresponding thread in users forum, so I’m posting here]

Oh, the dreadful:

error: cannot move out of borrowed content

fn f(tmp: &mut Option<Vec<u8>>) {
    let tmpfoo = &mut tmp.unwrap();
}

fn main() {
    f(&mut Some(Vec::new()));
}

Is unwrap really taking ownership!? I’m trying to unwrap to a borrowed reference, so it seems like something that should work.

[stebalien]

Unwrap takes self by value. However, you can go from a &mut Option<V> to an Option<&mut V> by using Option::as_mut():

fn f(tmp: &mut Option<Vec<u8>>) {
    let tmpfoo = tmp.as_mut().unwrap();
}

fn main() {
    f(&mut Some(Vec::new()));
}

[nikomatsakis]

[nikomatsakis]

I’ve unpinned this topic – we still need work here, but I think we’ve gathered enough examples.

[nikomatsakis]

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