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Explicitly document how Send and Sync relate to references #111065

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May 2, 2023
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Explicitly document how Send and Sync relate to references #111065

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7 changes: 6 additions & 1 deletion library/core/src/marker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ use crate::hash::Hasher;
/// operations. Its cousin [`sync::Arc`][arc] does use atomic operations (incurring
/// some overhead) and thus is `Send`.
///
/// See [the Nomicon](../../nomicon/send-and-sync.html) for more details.
/// See [the Nomicon](../../nomicon/send-and-sync.html) and the [`Sync`] trait for more details.
///
/// [`Rc`]: ../../std/rc/struct.Rc.html
/// [arc]: ../../std/sync/struct.Arc.html
Expand Down Expand Up @@ -426,6 +426,11 @@ pub macro Copy($item:item) {
/// becomes read-only, as if it were a `& &T`. Hence there is no risk
/// of a data race.
///
/// A shorter overview of how [`Sync`] and [`Send`] relate to referencing:
/// * `&T` is [`Send`] if and only if `T` is [`Sync`]
/// * `&mut T` is [`Send`] if and only if `T` is [`Send`]
/// * `&T` and `&mut T` are [`Sync`] if and only if `T` is [`Sync`]
///
/// Types that are not `Sync` are those that have "interior
/// mutability" in a non-thread-safe form, such as [`Cell`][cell]
/// and [`RefCell`][refcell]. These types allow for mutation of
Expand Down