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nemo1618 • yesterday at 3:33 AM • 3 replies • view on HN

Conversely, I use this "block pattern" a lot, and sometimes it causes lifetime issues:

    let foo: &[SomeType] = {
        let mut foo = vec![];
        // ... initialize foo ...
        &foo
    };
This doesn't work: the memory is owned by the Vec, whose lifetime is tied to the block, so the slice is invalid outside of that block. To be fair, it's probably best to just make foo a Vec, and turn it into a slice where needed.

Replies

saghm • yesterday at 3:55 AM

Unless I'm misunderstanding, you'd have the same lifetime issue if you tried to move the block into a function, though. I think the parent comment's point is that it causes fewer issues than abstracting to a separate function, not necessarily compared to inlining everything.

adrianN • yesterday at 6:50 AM

Avoiding that kind of use after free problem is exactly why people choose Rust, isn’t it?

janquo • yesterday at 12:07 PM

There is some experimental work for that here I believe:

https://doc.rust-lang.org/beta/unstable-book/language-featur...

AFAIU it essentially creates a variable in inner scope but defers drop to the outer scope so that you can return the reference