std::sync::Weak
Struct std::sync::Weak
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 upgrade
d.
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]
fn new() -> Weak<T>
1.10.0
Constructs a new Weak<T>
, allocating memory for T
without initializing it. Calling upgrade
on the return value always gives None
.
Examples
use std::sync::Weak; let empty: Weak<i64> = Weak::new(); assert!(empty.upgrade().is_none());
impl<T> Weak<T> where
T: ?Sized,
[src]
T: ?Sized,
fn upgrade(&self) -> Option<Arc<T>>
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());
Trait Implementations
impl<T> Sync for Weak<T> where
T: Send + Sync + ?Sized,
[src]
T: Send + Sync + ?Sized,
impl<T> Debug for Weak<T> where
T: Debug + ?Sized,
[src]
T: Debug + ?Sized,
fn fmt(&self, f: &mut Formatter) -> Result<(), Error>
Formats the value using the given formatter.
impl<T> Drop for Weak<T> where
T: ?Sized,
[src]
T: ?Sized,
fn drop(&mut self)
Drops the Weak
pointer.
Examples
use std::sync::Arc; 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_foo.clone(); drop(weak_foo); // Doesn't print anything drop(foo); // Prints "dropped!" assert!(other_weak_foo.upgrade().is_none());
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> Clone for Weak<T> where
T: ?Sized,
[src]
T: ?Sized,
fn clone(&self) -> Weak<T>
Makes a clone of the Weak
pointer that points to the same value.
Examples
use std::sync::Arc; let weak_five = Arc::downgrade(&Arc::new(5)); weak_five.clone();
fn clone_from(&mut self, source: &Self)
1.0.0
Performs copy-assignment from source
. Read more
impl<T> Default for Weak<T>
1.10.0
[src]
fn default() -> Weak<T>
Constructs a new Weak<T>
, allocating memory for T
without initializing it. Calling upgrade
on the return value always gives None
.
Examples
use std::sync::Weak; let empty: Weak<i64> = Default::default(); assert!(empty.upgrade().is_none());
impl<T> Send for Weak<T> where
T: Send + Sync + ?Sized,
[src]
T: Send + Sync + ?Sized,
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/sync/struct.Weak.html