diff --git a/library/core/src/pin.rs b/library/core/src/pin.rs index 8d73bf56dcb0d..2a8a127b6cab5 100644 --- a/library/core/src/pin.rs +++ b/library/core/src/pin.rs @@ -6,7 +6,7 @@ //! as moving an object with pointers to itself will invalidate them, which could cause undefined //! behavior. //! -//! At a high level, a [`Pin
`] ensures that the pointee of any pointer type
+//! At a high level, a `] wraps a pointer type `P`, so `] does
-//! not let clients actually obtain a [`Box `] does *not* change the fact that a Rust compiler
-//! considers all types movable. [`mem::swap`] remains callable for any `T`. Instead, [`Pin `]
-//! prevents certain *values* (pointed to by pointers wrapped in [`Pin `]) from being
+//! It is worth reiterating that `] can be used to wrap any pointer type `P`, and as such it interacts with
-//! [`Deref`] and [`DerefMut`]. A [`Pin `] where `P: Deref` should be considered
+//! `] relies on the implementations of [`Deref`] and
+//! For correctness, `]. For `T: Unpin`,
-//! `]. For example, whether or not [`Box[Pin]\
ensures that the pointee of any pointer type
//! `P` has a stable location in memory, meaning it cannot be moved elsewhere
//! and its memory cannot be deallocated until it gets dropped. We say that the
//! pointee is "pinned". Things get more subtle when discussing types that
@@ -14,12 +14,12 @@
//! for more details.
//!
//! By default, all types in Rust are movable. Rust allows passing all types by-value,
-//! and common smart-pointer types such as [`Box[Pin]<[Box]\
functions much like a regular
-//! [`Box[Pin]<[Box]\
gets dropped, so do its contents, and the memory gets
-//! deallocated. Similarly, [Pin]<&mut T>
is a lot like `&mut T`. However, [`Pin[Box]\
and `&mut T` allow replacing and
+//! moving the values they contain: you can move out of a [Box]\
, or you can use [`mem::swap`].
+//! [Pin]\
wraps a pointer type `P`, so [Pin]<[Box]\
functions much like a regular
+//! [Box]\
: when a [Pin]<[Box]\
gets dropped, so do its contents, and the memory gets
+//! deallocated. Similarly, [Pin]<&mut T>
is a lot like `&mut T`. However, [Pin]\
does
+//! not let clients actually obtain a [Box]\
or `&mut T` to pinned data, which implies that you
//! cannot use operations such as [`mem::swap`]:
//!
//! ```
@@ -32,18 +32,18 @@
//! }
//! ```
//!
-//! It is worth reiterating that [`Pin[Pin]\
does *not* change the fact that a Rust compiler
+//! considers all types movable. [`mem::swap`] remains callable for any `T`. Instead, [Pin]\
+//! prevents certain *values* (pointed to by pointers wrapped in [Pin]\
) from being
//! moved by making it impossible to call methods that require `&mut T` on them
//! (like [`mem::swap`]).
//!
-//! [`Pin[Pin]\
can be used to wrap any pointer type `P`, and as such it interacts with
+//! [`Deref`] and [`DerefMut`]. A [Pin]\
where `P: Deref` should be considered
//! as a "`P`-style pointer" to a pinned `P::Target` -- so, a [Pin]<[Box]\
is
//! an owned pointer to a pinned `T`, and a [Pin]<[Rc]\
is a reference-counted
//! pointer to a pinned `T`.
-//! For correctness, [`Pin[Pin]\
relies on the implementations of [`Deref`] and
//! [`DerefMut`] not to move out of their `self` parameter, and only ever to
//! return a pointer to pinned data when they are called on a pinned pointer.
//!
@@ -53,12 +53,12 @@
//! rely on having a stable address. This includes all the basic types (like
//! [`bool`], [`i32`], and references) as well as types consisting solely of these
//! types. Types that do not care about pinning implement the [`Unpin`]
-//! auto-trait, which cancels the effect of [`Pin[Pin]<[Box]\
and [`Box[Pin]<&mut T>
and
+//! auto-trait, which cancels the effect of [Pin]\
. For `T: Unpin`,
+//! [Pin]<[Box]\
and [Box]\
function identically, as do [Pin]<&mut T>
and
//! `&mut T`.
//!
//! Note that pinning and [`Unpin`] only affect the pointed-to type `P::Target`, not the pointer
-//! type `P` itself that got wrapped in [`Pin[Pin]\
. For example, whether or not [Box]\
is
//! [`Unpin`] has no effect on the behavior of [Pin]<[Box]\
(here, `T` is the
//! pointed-to type).
//!
@@ -149,7 +149,7 @@
//! when [`drop`] is called*. Only once [`drop`] returns or panics, the memory may be reused.
//!
//! Memory can be "invalidated" by deallocation, but also by
-//! replacing a [`Some(v)`] by [`None`], or calling [`Vec::set_len`] to "kill" some elements
+//! replacing a [Some]\(v)
by [`None`], or calling [`Vec::set_len`] to "kill" some elements
//! off of a vector. It can be repurposed by using [`ptr::write`] to overwrite it without
//! calling the destructor first. None of this is allowed for pinned data without calling [`drop`].
//!
@@ -209,7 +209,7 @@
//! that turn [Pin]<&mut Struct>
into a reference to the field, but what
//! type should that reference have? Is it [Pin]<&mut Field>
or `&mut Field`?
//! The same question arises with the fields of an `enum`, and also when considering
-//! container/wrapper types such as [`Vec[Vec]\
, [Box]\
, or [RefCell]\
.
//! (This question applies to both mutable and shared references, we just
//! use the more common case of mutable references here for illustration.)
//!
@@ -292,19 +292,19 @@
//! 3. You must make sure that you uphold the [`Drop` guarantee][drop-guarantee]:
//! once your struct is pinned, the memory that contains the
//! content is not overwritten or deallocated without calling the content's destructors.
-//! This can be tricky, as witnessed by [`VecDeque[VecDeque]\
: the destructor of [VecDeque]\
//! can fail to call [`drop`] on all elements if one of the destructors panics. This violates
//! the [`Drop`] guarantee, because it can lead to elements being deallocated without
-//! their destructor being called. ([`VecDeque[VecDeque]\
has no pinning projections, so this
//! does not cause unsoundness.)
//! 4. You must not offer any other operations that could lead to data being moved out of
//! the structural fields when your type is pinned. For example, if the struct contains an
-//! [`Option[Option]\
and there is a `take`-like operation with type
//! `fn(Pin<&mut Struct[RefCell]\
//! had a method `fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut T>`.
//! Then we could do the following:
//! ```compile_fail
@@ -315,30 +315,30 @@
//! let content = &mut *b; // And here we have `&mut T` to the same data.
//! }
//! ```
-//! This is catastrophic, it means we can first pin the content of the [`RefCell[RefCell]\
//! (using `RefCell::get_pin_mut`) and then move that content using the mutable
//! reference we got later.
//!
//! ## Examples
//!
-//! For a type like [`Vec[Vec]\
, both possibilities (structural pinning or not) make sense.
+//! A [Vec]\
with structural pinning could have `get_pin`/`get_pin_mut` methods to get
//! pinned references to elements. However, it could *not* allow calling
-//! [`pop`][Vec::pop] on a pinned [`Vec[Vec]\
because that would move the (structurally pinned)
//! contents! Nor could it allow [`push`][Vec::push], which might reallocate and thus also move the
//! contents.
//!
-//! A [`Vec[Vec]\
without structural pinning could `impl[Vec]\
itself is fine with being moved as well.
//! At that point pinning just has no effect on the vector at all.
//!
//! In the standard library, pointer types generally do not have structural pinning,
//! and thus they do not offer pinning projections. This is why `Box[Box]\
can be freely movable (aka `Unpin`) even if
//! the `T` is not. In fact, even [Pin]<[Box]\
and [Pin]<&mut T>
are always
//! [`Unpin`] themselves, for the same reason: their contents (the `T`) are pinned, but the
-//! pointers themselves can be moved without moving the pinned data. For both [`Box[Box]\
and
//! [Pin]<[Box]\
, whether the content is pinned is entirely independent of whether the
//! pointer is pinned, meaning pinning is *not* structural.
//!
@@ -353,17 +353,15 @@
//! [`DerefMut`]: crate::ops::DerefMut
//! [`mem::swap`]: crate::mem::swap
//! [`mem::forget`]: crate::mem::forget
-//! [`Box