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Stabilize slice::strip_prefix and slice::strip_suffix #77853

Merged
merged 5 commits into from
Jan 7, 2021
Merged

Stabilize slice::strip_prefix and slice::strip_suffix #77853

merged 5 commits into from
Jan 7, 2021

Commits on Dec 27, 2020

  1. Stablize slice::strip_prefix and strip_suffix, with SlicePattern 

    We hope later to extend `core::str::Pattern` to slices too, perhaps as
part of stabilising that.  We want to minimise the amount of type
inference breakage when we do that, so we don't want to stabilise
strip_prefix and strip_suffix taking a simple `&[T]`.

@KodrAus suggested the approach of introducing a new perma-unstable
trait, which reduces this future inference break risk.

I found it necessary to make two impls of this trait, as the unsize
coercion don't apply when hunting for trait implementations.

Since SlicePattern's only method returns a reference, and the whole
trait is just a wrapper for slices, I made the trait type be the
non-reference type [T] or [T;N] rather than the reference.  Otherwise
the trait would have a lifetime parameter.

I marked both the no-op conversion functions `#[inline]`.  I'm not
sure if that is necessary but it seemed at the very least harmless.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
    @ijackson
    ijackson committed Dec 27, 2020
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  2. Use existing slice_pattern feature for SlicePattern 

    Co-authored-by: Ashley Mannix <kodraus@hey.com>
    @ijackson @KodrAus
    ijackson and KodrAus committed Dec 27, 2020
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  3. Drop pointless as_slice call. 

    Co-authored-by: David Tolnay <dtolnay@gmail.com>
    @ijackson @dtolnay
    ijackson and dtolnay committed Dec 27, 2020
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  4. Mark SlicePattern trait uses as ?Sized 

    This trait is ?Sized and is often slices.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
    @ijackson
    ijackson committed Dec 27, 2020
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  5. Add test for slice as prefix/suffix pattern 

    Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
    @ijackson
    ijackson committed Dec 27, 2020
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