Add some links to the cell docs.

This commit is contained in:
Eric Huss 2021-01-30 13:07:24 -08:00
parent fd20a8be0d
commit 4749ad0912

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@ -11,12 +11,10 @@
//! mutate it.
//!
//! Shareable mutable containers exist to permit mutability in a controlled manner, even in the
//! presence of aliasing. Both `Cell<T>` and `RefCell<T>` allow doing this in a single-threaded
//! presence of aliasing. Both [`Cell<T>`] and [`RefCell<T>`] allow doing this in a single-threaded
//! way. However, neither `Cell<T>` nor `RefCell<T>` are thread safe (they do not implement
//! `Sync`). If you need to do aliasing and mutation between multiple threads it is possible to
//! use [`Mutex`](../../std/sync/struct.Mutex.html),
//! [`RwLock`](../../std/sync/struct.RwLock.html) or
//! [`atomic`](../../core/sync/atomic/index.html) types.
//! [`Sync`]). If you need to do aliasing and mutation between multiple threads it is possible to
//! use [`Mutex<T>`], [`RwLock<T>`] or [`atomic`] types.
//!
//! Values of the `Cell<T>` and `RefCell<T>` types may be mutated through shared references (i.e.
//! the common `&T` type), whereas most Rust types can only be mutated through unique (`&mut T`)
@ -28,13 +26,14 @@
//! one must use the `RefCell<T>` type, acquiring a write lock before mutating. `Cell<T>` provides
//! methods to retrieve and change the current interior value:
//!
//! - For types that implement `Copy`, the `get` method retrieves the current interior value.
//! - For types that implement `Default`, the `take` method replaces the current interior value
//! with `Default::default()` and returns the replaced value.
//! - For all types, the `replace` method replaces the current interior value and returns the
//! replaced value and the `into_inner` method consumes the `Cell<T>` and returns the interior
//! value. Additionally, the `set` method replaces the interior value, dropping the replaced
//! value.
//! - For types that implement [`Copy`], the [`get`](Cell::get) method retrieves the current
//! interior value.
//! - For types that implement [`Default`], the [`take`](Cell::take) method replaces the current
//! interior value with [`Default::default()`] and returns the replaced value.
//! - For all types, the [`replace`](Cell::replace) method replaces the current interior value and
//! returns the replaced value and the [`into_inner`](Cell::into_inner) method consumes the
//! `Cell<T>` and returns the interior value. Additionally, the [`set`](Cell::set) method
//! replaces the interior value, dropping the replaced value.
//!
//! `RefCell<T>` uses Rust's lifetimes to implement 'dynamic borrowing', a process whereby one can
//! claim temporary, exclusive, mutable access to the inner value. Borrows for `RefCell<T>`s are
@ -54,12 +53,12 @@
//!
//! * Introducing mutability 'inside' of something immutable
//! * Implementation details of logically-immutable methods.
//! * Mutating implementations of `Clone`.
//! * Mutating implementations of [`Clone`].
//!
//! ## Introducing mutability 'inside' of something immutable
//!
//! Many shared smart pointer types, including `Rc<T>` and `Arc<T>`, provide containers that can be
//! cloned and shared between multiple parties. Because the contained values may be
//! Many shared smart pointer types, including [`Rc<T>`] and [`Arc<T>`], provide containers that can
//! be cloned and shared between multiple parties. Because the contained values may be
//! multiply-aliased, they can only be borrowed with `&`, not `&mut`. Without cells it would be
//! impossible to mutate data inside of these smart pointers at all.
//!
@ -91,7 +90,7 @@
//! ```
//!
//! Note that this example uses `Rc<T>` and not `Arc<T>`. `RefCell<T>`s are for single-threaded
//! scenarios. Consider using `RwLock<T>` or `Mutex<T>` if you need shared mutability in a
//! scenarios. Consider using [`RwLock<T>`] or [`Mutex<T>`] if you need shared mutability in a
//! multi-threaded situation.
//!
//! ## Implementation details of logically-immutable methods
@ -127,10 +126,10 @@
//! ## Mutating implementations of `Clone`
//!
//! This is simply a special - but common - case of the previous: hiding mutability for operations
//! that appear to be immutable. The `clone` method is expected to not change the source value, and
//! is declared to take `&self`, not `&mut self`. Therefore, any mutation that happens in the
//! `clone` method must use cell types. For example, `Rc<T>` maintains its reference counts within a
//! `Cell<T>`.
//! that appear to be immutable. The [`clone`](Clone::clone) method is expected to not change the
//! source value, and is declared to take `&self`, not `&mut self`. Therefore, any mutation that
//! happens in the `clone` method must use cell types. For example, [`Rc<T>`] maintains its
//! reference counts within a `Cell<T>`.
//!
//! ```
//! use std::cell::Cell;
@ -185,6 +184,11 @@
//! }
//! ```
//!
//! [`Arc<T>`]: ../../std/sync/struct.Arc.html
//! [`Rc<T>`]: ../../std/rc/struct.Rc.html
//! [`RwLock<T>`]: ../../std/sync/struct.RwLock.html
//! [`Mutex<T>`]: ../../std/sync/struct.Mutex.html
//! [`atomic`]: ../../core/sync/atomic/index.html
#![stable(feature = "rust1", since = "1.0.0")]