Subtypes and trait objects

1

I want to write code like

struct MyError  {
    inner: Box<dyn Error + Send + Sync + 'static>,
}

impl Error for MyError {
    fn source(&self) -> &(dyn Error + 'static) {
        &self.inner
    }
}

but rust doesn't seem to figure out that Error + Send + Sync + 'static must also be Error + 'static. Am I missing something?

EDIT My example isn't correct. It should be

impl Error for MyError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        self.inner.as_ref().map(|e| &**e as &(dyn StdError + 'static))
    }
}

(note the as cast I need to make it work). Can I avoid the cast and still get it to compile?

2

Hi, you just forgot to dereference the Box

&*self.inner

the compiler thinks you're trying to return a &Box<dyn Error>.

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3

I would like to provide an example, but it seems I've broken the playground :cold_sweat:
Playground:

image
image911×586 33.4 KB

4

That's not you, the playground can't compile anything on nightly right now.

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