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| author | Frank Steffahn <frank.steffahn@stu.uni-kiel.de> | 2021-01-05 17:39:18 +0100 |
|---|---|---|
| committer | Frank Steffahn <frank.steffahn@stu.uni-kiel.de> | 2021-01-05 17:39:18 +0100 |
| commit | ceaeb249a3813a78bd81fa3890e27e8843a58262 (patch) | |
| tree | 6cba326dca9ccf84584207856c698383efaade00 | |
| parent | d3915c555ee016b11ce288e107e46dbab9f78c4f (diff) | |
| download | rust-ceaeb249a3813a78bd81fa3890e27e8843a58262.tar.gz rust-ceaeb249a3813a78bd81fa3890e27e8843a58262.zip | |
Exclude single type parameters from links in `core::pin` for more visual consistency.
| -rw-r--r-- | library/core/src/pin.rs | 68 |
1 files changed, 33 insertions, 35 deletions
diff --git a/library/core/src/pin.rs b/library/core/src/pin.rs index 8d73bf56dcb..2a8a127b6ca 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<P>`] ensures that the pointee of any pointer type +//! At a high level, a <code>[Pin]\<P></code> 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<T>`] and `&mut T` allow replacing and -//! moving the values they contain: you can move out of a [`Box<T>`], or you can use [`mem::swap`]. -//! [`Pin<P>`] wraps a pointer type `P`, so <code>[Pin]<[Box]\<T>></code> functions much like a regular -//! [`Box<T>`]: when a <code>[Pin]<[Box]\<T>></code> gets dropped, so do its contents, and the memory gets -//! deallocated. Similarly, <code>[Pin]<&mut T></code> is a lot like `&mut T`. However, [`Pin<P>`] does -//! not let clients actually obtain a [`Box<T>`] or `&mut T` to pinned data, which implies that you +//! and common smart-pointer types such as <code>[Box]\<T></code> and `&mut T` allow replacing and +//! moving the values they contain: you can move out of a <code>[Box]\<T></code>, or you can use [`mem::swap`]. +//! <code>[Pin]\<P></code> wraps a pointer type `P`, so <code>[Pin]<[Box]\<T>></code> functions much like a regular +//! <code>[Box]\<T></code>: when a <code>[Pin]<[Box]\<T>></code> gets dropped, so do its contents, and the memory gets +//! deallocated. Similarly, <code>[Pin]<&mut T></code> is a lot like `&mut T`. However, <code>[Pin]\<P></code> does +//! not let clients actually obtain a <code>[Box]\<T></code> 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<P>`] does *not* change the fact that a Rust compiler -//! considers all types movable. [`mem::swap`] remains callable for any `T`. Instead, [`Pin<P>`] -//! prevents certain *values* (pointed to by pointers wrapped in [`Pin<P>`]) from being +//! It is worth reiterating that <code>[Pin]\<P></code> does *not* change the fact that a Rust compiler +//! considers all types movable. [`mem::swap`] remains callable for any `T`. Instead, <code>[Pin]\<P></code> +//! prevents certain *values* (pointed to by pointers wrapped in <code>[Pin]\<P></code>) from being //! moved by making it impossible to call methods that require `&mut T` on them //! (like [`mem::swap`]). //! -//! [`Pin<P>`] can be used to wrap any pointer type `P`, and as such it interacts with -//! [`Deref`] and [`DerefMut`]. A [`Pin<P>`] where `P: Deref` should be considered +//! <code>[Pin]\<P></code> can be used to wrap any pointer type `P`, and as such it interacts with +//! [`Deref`] and [`DerefMut`]. A <code>[Pin]\<P></code> where `P: Deref` should be considered //! as a "`P`-style pointer" to a pinned `P::Target` -- so, a <code>[Pin]<[Box]\<T>></code> is //! an owned pointer to a pinned `T`, and a <code>[Pin]<[Rc]\<T>></code> is a reference-counted //! pointer to a pinned `T`. -//! For correctness, [`Pin<P>`] relies on the implementations of [`Deref`] and +//! For correctness, <code>[Pin]\<P></code> 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<P>`]. For `T: Unpin`, -//! <code>[Pin]<[Box]\<T>></code> and [`Box<T>`] function identically, as do <code>[Pin]<&mut T></code> and +//! auto-trait, which cancels the effect of <code>[Pin]\<P></code>. For `T: Unpin`, +//! <code>[Pin]<[Box]\<T>></code> and <code>[Box]\<T></code> function identically, as do <code>[Pin]<&mut T></code> 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<P>`]. For example, whether or not [`Box<T>`] is +//! type `P` itself that got wrapped in <code>[Pin]\<P></code>. For example, whether or not <code>[Box]\<T></code> is //! [`Unpin`] has no effect on the behavior of <code>[Pin]<[Box]\<T>></code> (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 <code>[Some]\(v)</code> 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 <code>[Pin]<&mut Struct></code> into a reference to the field, but what //! type should that reference have? Is it <code>[Pin]<&mut Field></code> or `&mut Field`? //! The same question arises with the fields of an `enum`, and also when considering -//! container/wrapper types such as [`Vec<T>`], [`Box<T>`], or [`RefCell<T>`]. +//! container/wrapper types such as <code>[Vec]\<T></code>, <code>[Box]\<T></code>, or <code>[RefCell]\<T></code>. //! (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<T>`]: the destructor of [`VecDeque<T>`] +//! This can be tricky, as witnessed by <code>[VecDeque]\<T></code>: the destructor of <code>[VecDeque]\<T></code> //! 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<T>`] has no pinning projections, so this +//! their destructor being called. (<code>[VecDeque]\<T></code> 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<T>`] and there is a `take`-like operation with type +//! <code>[Option]\<T></code> and there is a `take`-like operation with type //! `fn(Pin<&mut Struct<T>>) -> Option<T>`, //! that operation can be used to move a `T` out of a pinned `Struct<T>` -- which means //! pinning cannot be structural for the field holding this data. //! -//! For a more complex example of moving data out of a pinned type, imagine if [`RefCell<T>`] +//! For a more complex example of moving data out of a pinned type, imagine if <code>[RefCell]\<T></code> //! 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<T>`] +//! This is catastrophic, it means we can first pin the content of the <code>[RefCell]\<T></code> //! (using `RefCell::get_pin_mut`) and then move that content using the mutable //! reference we got later. //! //! ## Examples //! -//! For a type like [`Vec<T>`], both possibilities (structural pinning or not) make sense. -//! A [`Vec<T>`] with structural pinning could have `get_pin`/`get_pin_mut` methods to get +//! For a type like <code>[Vec]\<T></code>, both possibilities (structural pinning or not) make sense. +//! A <code>[Vec]\<T></code> 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<T>`] because that would move the (structurally pinned) +//! [`pop`][Vec::pop] on a pinned <code>[Vec]\<T></code> 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<T>`] without structural pinning could `impl<T> Unpin for Vec<T>`, because the contents -//! are never pinned and the [`Vec<T>`] itself is fine with being moved as well. +//! A <code>[Vec]\<T></code> without structural pinning could `impl<T> Unpin for Vec<T>`, because the contents +//! are never pinned and the <code>[Vec]\<T></code> 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<T>: Unpin` holds for all `T`. //! It makes sense to do this for pointer types, because moving the `Box<T>` -//! does not actually move the `T`: the [`Box<T>`] can be freely movable (aka `Unpin`) even if +//! does not actually move the `T`: the <code>[Box]\<T></code> can be freely movable (aka `Unpin`) even if //! the `T` is not. In fact, even <code>[Pin]<[Box]\<T>></code> and <code>[Pin]<&mut T></code> 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<T>`] and +//! pointers themselves can be moved without moving the pinned data. For both <code>[Box]\<T></code> and //! <code>[Pin]<[Box]\<T>></code>, 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<T>`]: ../../std/boxed/struct.Box.html -//! [`Vec<T>`]: ../../std/vec/struct.Vec.html +//! [Vec]: ../../std/vec/struct.Vec.html //! [`Vec::set_len`]: ../../std/vec/struct.Vec.html#method.set_len //! [Box]: ../../std/boxed/struct.Box.html //! [Vec::pop]: ../../std/vec/struct.Vec.html#method.pop //! [Vec::push]: ../../std/vec/struct.Vec.html#method.push //! [Rc]: ../../std/rc/struct.Rc.html -//! [`RefCell<T>`]: crate::cell::RefCell +//! [RefCell]: crate::cell::RefCell //! [`drop`]: Drop::drop -//! [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html -//! [`Some(v)`]: Some +//! [VecDeque]: ../../std/collections/struct.VecDeque.html //! [`ptr::write`]: crate::ptr::write //! [`Future`]: crate::future::Future //! [drop-impl]: #drop-implementation |
