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Rollup merge of #60727 - chpio:master, r=sfackler

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add comment to `Rc`/`Arc`'s `Eq` specialization

in addition to https://github.com/rust-lang/rust/pull/56550

https://github.com/rust-lang/rust/pull/42965#issuecomment-312702479
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Mazdak Farrokhzad 2019-05-11 23:41:38 +02:00 committed by GitHub
commit e19ad45107
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5
src/liballoc/rc.rs
View File

@ -932,6 +932,11 @@ impl<T: ?Sized + PartialEq> RcEqIdent<T> for Rc<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 `Rc`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 `Rc` clones, that point to
/// the same value, than two `&T`s.
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Eq> RcEqIdent<T> for Rc<T> {
#[inline]

5
src/liballoc/sync.rs
View File

@ -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]