//! [downgrade]: struct.Rc.html#method.downgrade
//! [upgrade]: struct.Weak.html#method.upgrade
//! [`None`]: ../../std/option/enum.Option.html#variant.None
-//! [assoc]: ../../book/method-syntax.html#associated-functions
+//! [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
//! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable
#![stable(feature = "rust1", since = "1.0.0")]
}
}
-/// A weak version of [`Rc`][rc].
+/// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
+/// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
+/// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`.
///
-/// `Weak` pointers do not count towards determining if the inner value
-/// should be dropped.
+/// Since a `Weak` reference does not count towards ownership, it will not
+/// prevent the inner value from being dropped, and `Weak` itself makes no
+/// guarantees about the value still being present and may return [`None`]
+/// when [`upgrade`]d.
///
-/// The typical way to obtain a `Weak` pointer is to call
-/// [`Rc::downgrade`][downgrade].
+/// A `Weak` pointer is useful for keeping a temporary reference to the value
+/// within [`Rc`] without extending its lifetime. It is also used to prevent
+/// circular references between [`Rc`] pointers, since mutual owning references
+/// would never allow either [`Arc`] to be dropped. For example, a tree could
+/// have strong [`Rc`] pointers from parent nodes to children, and `Weak`
+/// pointers from children back to their parents.
///
-/// See the [module-level documentation](./index.html) for more details.
+/// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
///
-/// [rc]: struct.Rc.html
-/// [downgrade]: struct.Rc.html#method.downgrade
+/// [`Rc`]: struct.Rc.html
+/// [`Rc::downgrade`]: struct.Rc.html#method.downgrade
+/// [`upgrade`]: struct.Weak.html#method.upgrade
+/// [`Option`]: ../../std/option/enum.Option.html
+/// [`None`]: ../../std/option/enum.Option.html#variant.None
#[stable(feature = "rc_weak", since = "1.4.0")]
pub struct Weak<T: ?Sized> {
ptr: Shared<RcBox<T>>,
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
impl<T> Weak<T> {
- /// Constructs a new `Weak<T>`, without an accompanying instance of `T`.
- ///
- /// This allocates memory for `T`, but does not initialize it. Calling
- /// [`upgrade`][upgrade] on the return value always gives
- /// [`None`][option].
+ /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
+ /// it. Calling [`upgrade`] on the return value always gives [`None`].
///
- /// [upgrade]: struct.Weak.html#method.upgrade
- /// [option]: ../../std/option/enum.Option.html
+ /// [`upgrade`]: struct.Weak.html#method.upgrade
+ /// [`None`]: ../../std/option/enum.Option.html
///
/// # Examples
///
}
impl<T: ?Sized> Weak<T> {
- /// Upgrades the `Weak` pointer to an [`Rc`][rc], if possible.
+ /// Attempts to upgrade the `Weak` pointer to an [`Rc`], extending
+ /// the lifetime of the value if successful.
///
- /// Returns [`None`][option] if the strong count has reached zero and the
- /// inner value was destroyed.
+ /// Returns [`None`] if the value has since been dropped.
///
- /// [rc]: struct.Rc.html
- /// [option]: ../../std/option/enum.Option.html
+ /// [`Rc`]: struct.Rc.html
+ /// [`None`]: ../../std/option/enum.Option.html
///
/// # Examples
///
impl<T: ?Sized> Drop for Weak<T> {
/// Drops the `Weak` pointer.
///
- /// This will decrement the weak reference count.
- ///
/// # Examples
///
/// ```
#[stable(feature = "rc_weak", since = "1.4.0")]
impl<T: ?Sized> Clone for Weak<T> {
- /// Makes a clone of the `Weak` pointer.
- ///
- /// This creates another pointer to the same inner value, increasing the
- /// weak reference count.
+ /// Makes a clone of the `Weak` pointer that points to the same value.
///
/// # Examples
///
#[stable(feature = "downgraded_weak", since = "1.10.0")]
impl<T> Default for Weak<T> {
- /// Constructs a new `Weak<T>`, without an accompanying instance of `T`.
- ///
- /// This allocates memory for `T`, but does not initialize it. Calling
- /// [`upgrade`][upgrade] on the return value always gives
- /// [`None`][option].
+ /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
+ /// it. Calling [`upgrade`] on the return value always gives [`None`].
///
- /// [upgrade]: struct.Weak.html#method.upgrade
- /// [option]: ../../std/option/enum.Option.html
+ /// [`upgrade`]: struct.Weak.html#method.upgrade
+ /// [`None`]: ../../std/option/enum.Option.html
///
/// # Examples
///