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core: check for pointer equality when comparing Eq slices #61665

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Merged
merged 2 commits into from
Jul 11, 2019
Merged

core: check for pointer equality when comparing Eq slices #61665

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30b27f3
core: check for pointer equality when comparing Eq slices
aschampion Jun 8, 2019
d482589
core: use iterators for slice equality comparison
aschampion Jun 8, 2019
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25 changes: 24 additions & 1 deletion src/libcore/slice/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5304,6 +5304,29 @@ impl<A, B> SlicePartialEq<B> for [A]
}
}

// Use an equal-pointer optimization when types are `Eq`
impl<A> SlicePartialEq<A> for [A]
where A: PartialEq<A> + Eq
{
default fn equal(&self, other: &[A]) -> bool {
if self.len() != other.len() {
return false;
}

if self.as_ptr() == other.as_ptr() {
return true;
}

for i in 0..self.len() {
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This could be written as:

        self.iter().zip(other.iter()).all(|(x, y)| x == y)

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Good point. I mindlessly copied the other impl, but as written it's not clear the bounds check for other[i] would always be elided. I've updated both impls to user iterators now.

if !self[i].eq(&other[i]) {
return false;
}
}

true
}
}

// Use memcmp for bytewise equality when the types allow
impl<A> SlicePartialEq<A> for [A]
where A: PartialEq<A> + BytewiseEquality
Expand Down Expand Up @@ -5409,7 +5432,7 @@ impl SliceOrd<u8> for [u8] {
#[doc(hidden)]
/// Trait implemented for types that can be compared for equality using
/// their bytewise representation
trait BytewiseEquality { }
trait BytewiseEquality: Eq + Copy { }

macro_rules! impl_marker_for {
($traitname:ident, $($ty:ty)*) => {
Expand Down