diff options
Diffstat (limited to 'src/liballoc/sync.rs')
| -rw-r--r-- | src/liballoc/sync.rs | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs index 466e806663c..90c7859b3db 100644 --- a/src/liballoc/sync.rs +++ b/src/liballoc/sync.rs @@ -1377,6 +1377,11 @@ impl<T: ?Sized + PartialEq> ArcEqIdent<T> for Arc<T> { } } +/// We're doing this specialization here, and not as a more general optimization on `&T`, because it +/// would otherwise add a cost to all equality checks on refs. We assume that `Arc`s are used to +/// store large values, that are slow to clone, but also heavy to check for equality, causing this +/// cost to pay off more easily. It's also more likely to have two `Arc` clones, that point to +/// the same value, than two `&T`s. #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Eq> ArcEqIdent<T> for Arc<T> { #[inline] |