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DST coercions do not work in slices #16864

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huonw opened this issue Aug 30, 2014 · 3 comments
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DST coercions do not work in slices #16864

huonw opened this issue Aug 30, 2014 · 3 comments
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A-DSTs Area: Dynamically-sized types (DSTs)

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@huonw
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huonw commented Aug 30, 2014 

fn main() {
    let x: &[uint] = &[1u];
    let _y = &[x, &[1, 2]];
}
<anon>:3:19: 3:26 error: mismatched types: expected `&[uint]`, found `&[uint, .. 2]` (expected vector, found vector)
<anon>:3     let _y = &[x, &[1, 2]];
                           ^~~~~~~

This may not be a bug, but it does mean that slices constructed like this need to have type annotations.
@huonw huonw added the A-dst label Aug 30, 2014
@huonw huonw mentioned this issue Aug 30, 2014
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@bkoropoff bkoropoff mentioned this issue Sep 15, 2014
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@steveklabnik
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Triage: this is still true. Also not sure if it's a bug. @nikomatsakis ?

@huonw huonw mentioned this issue Jan 8, 2016
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@eddyb
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eddyb commented Jan 8, 2016

This is because we propagate the expected type downwards but not rightwards (from x to &[1, 2]).
We probably should do this by taking x's type after applying the outer expected type on it (and repeat this for any array element, so they can each add more information for the next one).

@Mark-Simulacrum
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With the code updated, this no longer causes an error. Closing.

fn main() {
    let x: &[u32] = &[1u32];
    let _y = &[x, &[1, 2]];
}

bors added a commit to rust-lang-ci/rust that referenced this issue Mar 31, 2024
@bors
Auto merge of rust-lang#16864 - lnicola:sync-from-rust, r=lnicola
3d39ddf 
internal: Sync from downstream
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@steveklabnik @eddyb @huonw @Mark-Simulacrum