Constructs a new Weak<T>, without an accompanying instance of T.

This allocates memory for T, but does not initialize 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());

Upgrades the Weak pointer to an Arc, if possible.

Returns None if the strong count has reached zero and the inner value was destroyed.

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());

Makes a clone of the Weak pointer.

This creates another pointer to the same inner value, increasing the weak reference count.

Examples

use std::sync::Arc;

let weak_five = Arc::downgrade(&Arc::new(5));

weak_five.clone();

Performs copy-assignment from source. Read more

Formats the value using the given formatter.

Constructs a new Weak<T>, without an accompanying instance of T.

This allocates memory for T, but does not initialize 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());

Drops the Weak pointer.

This will decrement the weak reference count.

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());