Struct std::sync::Weak 1.4.0
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pub struct Weak<T> where
T: ?Sized, { /* fields omitted */ }Weak is a version of Arc 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<Arc<T>>.
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 upgraded.
A Weak pointer is useful for keeping a temporary reference to the value
within Arc without extending its lifetime. It is also used to prevent
circular references between Arc pointers, since mutual owning references
would never allow either Arc to be dropped. For example, a tree could
have strong Arc pointers from parent nodes to children, and Weak
pointers from children back to their parents.
The typical way to obtain a Weak pointer is to call Arc::downgrade.
Methods
impl<T> Weak<T>[src]
impl<T> Weak<T> where
T: ?Sized, [src]
T: ?Sized,
fn upgrade(&self) -> Option<Arc<T>>[src]
Attempts to upgrade the Weak pointer to an Arc, extending
the lifetime of the value if successful.
Returns None if the value has since been dropped.
Examples
use std::sync::Arc; let five = Arc::new(5); let weak_five = Arc::downgrade(&five); let strong_five: Option<Arc<_>> = weak_five.upgrade(); assert!(strong_five.is_some()); // Destroy all strong pointers. drop(strong_five); drop(five); assert!(weak_five.upgrade().is_none());Run
Trait Implementations
impl<T, U> CoerceUnsized<Weak<U>> for Weak<T> where
T: Unsize<U> + ?Sized,
U: ?Sized, [src]
T: Unsize<U> + ?Sized,
U: ?Sized,
impl<T> Drop for Weak<T> where
T: ?Sized, [src]
T: ?Sized,
fn drop(&mut self)[src]
Drops the Weak pointer.
Examples
use std::sync::{Arc, Weak}; struct Foo; impl Drop for Foo { fn drop(&mut self) { println!("dropped!"); } } let foo = Arc::new(Foo); let weak_foo = Arc::downgrade(&foo); let other_weak_foo = Weak::clone(&weak_foo); drop(weak_foo); // Doesn't print anything drop(foo); // Prints "dropped!" assert!(other_weak_foo.upgrade().is_none());Run
impl<T> Send for Weak<T> where
T: Send + Sync + ?Sized, [src]
T: Send + Sync + ?Sized,
impl<T> Default for Weak<T>1.10.0[src]
impl<T> Debug for Weak<T> where
T: Debug + ?Sized, [src]
T: Debug + ?Sized,
fn fmt(&self, f: &mut Formatter) -> Result<(), Error>[src]
Formats the value using the given formatter. Read more
impl<T> Sync for Weak<T> where
T: Send + Sync + ?Sized, [src]
T: Send + Sync + ?Sized,
impl<T> Clone for Weak<T> where
T: ?Sized, [src]
T: ?Sized,
fn clone(&self) -> Weak<T>[src]
Makes a clone of the Weak pointer that points to the same value.
Examples
use std::sync::{Arc, Weak}; let weak_five = Arc::downgrade(&Arc::new(5)); Weak::clone(&weak_five);Run
fn clone_from(&mut self, source: &Self)1.0.0[src]
Performs copy-assignment from source. Read more