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implement PartialEq<VecDeque<U>> for Vec<T>, &[T], &mut [T], [T; N], &[T; N] and &mut [T; N] #163753

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implement PartialEq<VecDeque<U>> for Vec<T>, &[T], &mut [T], [T; N], &[T; N] and &mut [T; N] #163753

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20 changes: 20 additions & 0 deletions library/alloc/src/collections/vec_deque/macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,3 +17,23 @@ macro_rules! __impl_slice_eq1 {
}
}
}

macro_rules! __impl_slice_eq2 {
($(#[$stability:meta])+, [$($vars:tt)*] $lhs:ty, $rhs:ty, $($constraints:tt)*) => {
$(#[$stability])+
impl<T, U, A: Allocator, $($vars)*> PartialEq<$rhs> for $lhs
where
T: PartialEq<U>,
$($constraints)*
{
fn eq(&self, other: &$rhs) -> bool {
if self.len() != other.len() {
return false;
}
let (oa, ob) = other.as_slices();
let (sa, sb) = self[..].split_at(oa.len());
sa == oa && sb == ob
}
}
}
}
7 changes: 7 additions & 0 deletions library/alloc/src/collections/vec_deque/mod.rs
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Expand Up @@ -3907,6 +3907,13 @@ __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, [U; N], }
__impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &[U; N], }
__impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &mut [U; N], }

__impl_slice_eq2! { #[stable(feature = "slice_partial_eq_vec_deque", since = "CURRENT_RUSTC_VERSION")], [] Vec<T, A>, VecDeque<U, A>, }

@pthariensflame pthariensflame Oct 22, 2026 •
edited by rustbot
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Why are the two allocators both A? Is there a reason to restrict to only comparing a Vec and VecDeque using the same allocator?

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@clarfonthey clarfonthey Oct 22, 2026

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Valid point, and I think unfortunately this might warrant another crater run to fix. Although it's worth clarifying that only Vec stably supports allocators at the moment.

@pthariensflame pthariensflame Oct 22, 2026

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Although it's worth clarifying that only Vec stably supports allocators at the moment.

We did think of that but it doesn’t actually make a difference to this generalization. Vec having a choice of allocators means we may want to compare it with an arbitrary allocator to VecDeque<_, Global>.

__impl_slice_eq2! { #[stable(feature = "slice_partial_eq_vec_deque", since = "CURRENT_RUSTC_VERSION")], [] &[T], VecDeque<U, A>, }
__impl_slice_eq2! { #[stable(feature = "slice_partial_eq_vec_deque", since = "CURRENT_RUSTC_VERSION")], [] &mut [T], VecDeque<U, A>, }
__impl_slice_eq2! { #[stable(feature = "slice_partial_eq_vec_deque", since = "CURRENT_RUSTC_VERSION")], [const N: usize] [T; N], VecDeque<U, A>, }
__impl_slice_eq2! { #[stable(feature = "slice_partial_eq_vec_deque", since = "CURRENT_RUSTC_VERSION")], [const N: usize] &[T; N], VecDeque<U, A>, }
__impl_slice_eq2! { #[stable(feature = "slice_partial_eq_vec_deque", since = "CURRENT_RUSTC_VERSION")], [const N: usize] &mut [T; N], VecDeque<U, A>, }

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: PartialOrd, A: Allocator> PartialOrd for VecDeque<T, A> {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
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21 changes: 21 additions & 0 deletions library/alloctests/tests/vec_deque.rs
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Expand Up @@ -631,6 +631,27 @@ fn test_partial_eq_array() {
assert!(d == ['a', 'b']);
}

#[test]
fn test_partial_eq_vecdeque_reverse() {
let mut d = VecDeque::with_capacity(4);
d.push_back(1);
d.push_back(2);
d.push_back(3);
d.pop_front();
d.push_back(4);

let v = vec![2, 3, 4];
let a = [2, 3, 4];
let mut b = [2, 3, 4];

assert!(v == d);
assert!(&v[..] == d);
assert!(&mut b[..] == d);
assert!(a == d);
assert!(&a == d);
assert!(&mut b == d);
}

#[test]
fn test_hash() {
let mut x = VecDeque::new();
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6 changes: 3 additions & 3 deletions tests/ui/consts/too_generic_eval_ice.current.stderr
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Expand Up @@ -30,15 +30,15 @@ LL | [5; Self::HOST_SIZE] == [6; 0]
|
= help: the trait `PartialEq<[{integer}; 0]>` is not implemented for `[{integer}; Self::HOST_SIZE]`
= help: the following other types implement trait `PartialEq<Rhs>`:
`&[T; N]` implements `PartialEq<VecDeque<U, A>>`
`&[T]` implements `PartialEq<Cow<'_, [U]>>`
`&[T]` implements `PartialEq<Vec<U, A>>`
`&[T]` implements `PartialEq<VecDeque<U, A>>`
`&[T]` implements `PartialEq<[U; N]>`
`&[u8; N]` implements `PartialEq<ByteStr>`
`&[u8; N]` implements `PartialEq<ByteString>`
`&[u8]` implements `PartialEq<ByteStr>`
`&[u8]` implements `PartialEq<ByteString>`
`&mut [T]` implements `PartialEq<Cow<'_, [U]>>`
and 13 others
and 18 others

error: aborting due to 4 previous errors

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12 changes: 6 additions & 6 deletions tests/ui/macros/assert-ne-no-invalid-help-issue-146204.stderr
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Expand Up @@ -6,15 +6,15 @@ LL | assert_ne!(buf, b"----");
|
= help: the trait `PartialEq<&[u8; 4]>` is not implemented for `[u8; 4]`
= help: the following other types implement trait `PartialEq<Rhs>`:
`&[T; N]` implements `PartialEq<VecDeque<U, A>>`
`&[T]` implements `PartialEq<Cow<'_, [U]>>`
`&[T]` implements `PartialEq<Vec<U, A>>`
`&[T]` implements `PartialEq<VecDeque<U, A>>`
`&[T]` implements `PartialEq<[U; N]>`
`&[u8; N]` implements `PartialEq<ByteStr>`
`&[u8; N]` implements `PartialEq<ByteString>`
`&[u8]` implements `PartialEq<ByteStr>`
`&[u8]` implements `PartialEq<ByteString>`
`&mut [T]` implements `PartialEq<Cow<'_, [U]>>`
and 13 others
and 18 others

error[E0277]: can't compare `[u8; 4]` with `&[u8; 4]`
--> $DIR/assert-ne-no-invalid-help-issue-146204.rs:19:5
Expand All @@ -24,15 +24,15 @@ LL | assert_eq!(buf, b"----");
|
= help: the trait `PartialEq<&[u8; 4]>` is not implemented for `[u8; 4]`
= help: the following other types implement trait `PartialEq<Rhs>`:
`&[T; N]` implements `PartialEq<VecDeque<U, A>>`
`&[T]` implements `PartialEq<Cow<'_, [U]>>`
`&[T]` implements `PartialEq<Vec<U, A>>`
`&[T]` implements `PartialEq<VecDeque<U, A>>`
`&[T]` implements `PartialEq<[U; N]>`
`&[u8; N]` implements `PartialEq<ByteStr>`
`&[u8; N]` implements `PartialEq<ByteString>`
`&[u8]` implements `PartialEq<ByteStr>`
`&[u8]` implements `PartialEq<ByteString>`
`&mut [T]` implements `PartialEq<Cow<'_, [U]>>`
and 13 others
and 18 others

error[E0277]: can't compare `[u8; 4]` with `&[u8; 4]`
--> $DIR/assert-ne-no-invalid-help-issue-146204.rs:5:30
Expand Down
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