diff options
| -rw-r--r-- | library/core/src/pin.rs | 46 |
1 files changed, 23 insertions, 23 deletions
diff --git a/library/core/src/pin.rs b/library/core/src/pin.rs index b2de0e16a17..8d73bf56dcb 100644 --- a/library/core/src/pin.rs +++ b/library/core/src/pin.rs @@ -16,9 +16,9 @@ //! 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 [`Pin`]`<`[`Box`]`<T>>` functions much like a regular -//! [`Box<T>`]: when a [`Pin`]`<`[`Box`]`<T>>` gets dropped, so do its contents, and the memory gets -//! deallocated. Similarly, [`Pin`]`<&mut T>` is a lot like `&mut T`. However, [`Pin<P>`] does +//! [`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 //! cannot use operations such as [`mem::swap`]: //! @@ -40,8 +40,8 @@ //! //! [`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 -//! as a "`P`-style pointer" to a pinned `P::Target` -- so, a [`Pin`]`<`[`Box`]`<T>>` is -//! an owned pointer to a pinned `T`, and a [`Pin`]`<`[`Rc`]`<T>>` is a reference-counted +//! 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 //! [`DerefMut`] not to move out of their `self` parameter, and only ever to @@ -54,12 +54,12 @@ //! [`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`, -//! [`Pin`]`<`[`Box`]`<T>>` and [`Box<T>`] function identically, as do [`Pin`]`<&mut T>` and +//! <code>[Pin]<[Box]\<T>></code> and [`Box<T>`] 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 -//! [`Unpin`] has no effect on the behavior of [`Pin`]`<`[`Box`]`<T>>` (here, `T` is the +//! [`Unpin`] has no effect on the behavior of <code>[Pin]<[Box]\<T>></code> (here, `T` is the //! pointed-to type). //! //! # Example: self-referential struct @@ -158,7 +158,7 @@ //! //! Notice that this guarantee does *not* mean that memory does not leak! It is still //! completely okay not ever to call [`drop`] on a pinned element (e.g., you can still -//! call [`mem::forget`] on a [`Pin`]`<`[`Box`]`<T>>`). In the example of the doubly-linked +//! call [`mem::forget`] on a <code>[Pin]<[Box]\<T>></code>). In the example of the doubly-linked //! list, that element would just stay in the list. However you may not free or reuse the storage //! *without calling [`drop`]*. //! @@ -172,9 +172,9 @@ //! This can never cause a problem in safe code because implementing a type that //! relies on pinning requires unsafe code, but be aware that deciding to make //! use of pinning in your type (for example by implementing some operation on -//! [`Pin`]`<&Self>` or [`Pin`]`<&mut Self>`) has consequences for your [`Drop`] +//! <code>[Pin]<&Self></code> or <code>[Pin]<&mut Self></code>) has consequences for your [`Drop`] //! implementation as well: if an element of your type could have been pinned, -//! you must treat [`Drop`] as implicitly taking [`Pin`]`<&mut Self>`. +//! you must treat [`Drop`] as implicitly taking <code>[Pin]<&mut Self></code>. //! //! For example, you could implement `Drop` as follows: //! @@ -204,10 +204,10 @@ //! # Projections and Structural Pinning //! //! When working with pinned structs, the question arises how one can access the -//! fields of that struct in a method that takes just [`Pin`]`<&mut Struct>`. +//! fields of that struct in a method that takes just <code>[Pin]<&mut Struct></code>. //! The usual approach is to write helper methods (so called *projections*) -//! 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`? +//! 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>`]. //! (This question applies to both mutable and shared references, we just @@ -215,7 +215,7 @@ //! //! It turns out that it is actually up to the author of the data structure //! to decide whether the pinned projection for a particular field turns -//! [`Pin`]`<&mut Struct>` into [`Pin`]`<&mut Field>` or `&mut Field`. There are some +//! <code>[Pin]<&mut Struct></code> into <code>[Pin]<&mut Field></code> or `&mut Field`. There are some //! constraints though, and the most important constraint is *consistency*: //! every field can be *either* projected to a pinned reference, *or* have //! pinning removed as part of the projection. If both are done for the same field, @@ -230,12 +230,12 @@ //! ## Pinning *is not* structural for `field` //! //! It may seem counter-intuitive that the field of a pinned struct might not be pinned, -//! but that is actually the easiest choice: if a [`Pin`]`<&mut Field>` is never created, +//! but that is actually the easiest choice: if a <code>[Pin]<&mut Field></code> is never created, //! nothing can go wrong! So, if you decide that some field does not have structural pinning, //! all you have to ensure is that you never create a pinned reference to that field. //! //! Fields without structural pinning may have a projection method that turns -//! [`Pin`]`<&mut Struct>` into `&mut Field`: +//! <code>[Pin]<&mut Struct></code> into `&mut Field`: //! //! ```rust,no_run //! # use std::pin::Pin; @@ -251,14 +251,14 @@ //! //! You may also `impl Unpin for Struct` *even if* the type of `field` //! is not [`Unpin`]. What that type thinks about pinning is not relevant -//! when no [`Pin`]`<&mut Field>` is ever created. +//! when no <code>[Pin]<&mut Field></code> is ever created. //! //! ## Pinning *is* structural for `field` //! //! The other option is to decide that pinning is "structural" for `field`, //! meaning that if the struct is pinned then so is the field. //! -//! This allows writing a projection that creates a [`Pin`]`<&mut Field>`, thus +//! This allows writing a projection that creates a <code>[Pin]<&mut Field></code>, thus //! witnessing that the field is pinned: //! //! ```rust,no_run @@ -336,17 +336,17 @@ //! 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 -//! the `T` is not. In fact, even [`Pin`]`<`[`Box`]`<T>>` and [`Pin`]`<&mut T>` are always +//! 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 -//! [`Pin`]`<`[`Box`]`<T>>`, whether the content is pinned is entirely independent of whether the +//! <code>[Pin]<[Box]\<T>></code>, whether the content is pinned is entirely independent of whether the //! pointer is pinned, meaning pinning is *not* structural. //! //! When implementing a [`Future`] combinator, you will usually need structural pinning //! for the nested futures, as you need to get pinned references to them to call [`poll`]. //! But if your combinator contains any other data that does not need to be pinned, //! you can make those fields not structural and hence freely access them with a -//! mutable reference even when you just have [`Pin`]`<&mut Self>` (such as in your own +//! mutable reference even when you just have <code>[Pin]<&mut Self></code> (such as in your own //! [`poll`] implementation). //! //! [`Deref`]: crate::ops::Deref @@ -356,10 +356,10 @@ //! [`Box<T>`]: ../../std/boxed/struct.Box.html //! [`Vec<T>`]: ../../std/vec/struct.Vec.html //! [`Vec::set_len`]: ../../std/vec/struct.Vec.html#method.set_len -//! [`Box`]: ../../std/boxed/struct.Box.html +//! [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 +//! [Rc]: ../../std/rc/struct.Rc.html //! [`RefCell<T>`]: crate::cell::RefCell //! [`drop`]: Drop::drop //! [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html |