Constructs a new Weak<T>, without allocating any memory. Calling upgrade on the return value always gives None.

Examples

use std::rc::Weak;

let empty: Weak<i64> = Weak::new();
assert!(empty.upgrade().is_none());

Returns a raw pointer to the object T pointed to by this Weak<T>.

The pointer is valid only if there are some strong references. The pointer may be dangling, unaligned or even null otherwise.

Examples

use std::rc::Rc;
use std::ptr;

let strong = Rc::new("hello".to_owned());
let weak = Rc::downgrade(&strong);
// Both point to the same object
assert!(ptr::eq(&*strong, weak.as_ptr()));
// The strong here keeps it alive, so we can still access the object.
assert_eq!("hello", unsafe { &*weak.as_ptr() });

drop(strong);
// But not any more. We can do weak.as_ptr(), but accessing the pointer would lead to
// undefined behaviour.
// assert_eq!("hello", unsafe { &*weak.as_ptr() });

Consumes the Weak<T> and turns it into a raw pointer.

This converts the weak pointer into a raw pointer, while still preserving the ownership of one weak reference (the weak count is not modified by this operation). It can be turned back into the Weak<T> with from_raw.

The same restrictions of accessing the target of the pointer as with as_ptr apply.

Examples

use std::rc::{Rc, Weak};

let strong = Rc::new("hello".to_owned());
let weak = Rc::downgrade(&strong);
let raw = weak.into_raw();

assert_eq!(1, Rc::weak_count(&strong));
assert_eq!("hello", unsafe { &*raw });

drop(unsafe { Weak::from_raw(raw) });
assert_eq!(0, Rc::weak_count(&strong));

Converts a raw pointer previously created by into_raw back into Weak<T>.

This can be used to safely get a strong reference (by calling upgrade later) or to deallocate the weak count by dropping the Weak<T>.

It takes ownership of one weak reference (with the exception of pointers created by new, as these don't own anything; the method still works on them).

Safety

The pointer must have originated from the into_raw and must still own its potential weak reference.

It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this takes ownership of one weak reference currently represented as a raw pointer (the weak count is not modified by this operation) and therefore it must be paired with a previous call to into_raw.

Examples

use std::rc::{Rc, Weak};

let strong = Rc::new("hello".to_owned());

let raw_1 = Rc::downgrade(&strong).into_raw();
let raw_2 = Rc::downgrade(&strong).into_raw();

assert_eq!(2, Rc::weak_count(&strong));

assert_eq!("hello", &*unsafe { Weak::from_raw(raw_1) }.upgrade().unwrap());
assert_eq!(1, Rc::weak_count(&strong));

drop(strong);

// Decrement the last weak count.
assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none());

Attempts to upgrade the Weak pointer to an Rc, delaying dropping of the inner value if successful.

Returns None if the inner value has since been dropped.

Examples

use std::rc::Rc;

let five = Rc::new(5);

let weak_five = Rc::downgrade(&five);

let strong_five: Option<Rc<_>> = weak_five.upgrade();
assert!(strong_five.is_some());

// Destroy all strong pointers.
drop(strong_five);
drop(five);

assert!(weak_five.upgrade().is_none());

Gets the number of strong (Rc) pointers pointing to this allocation.

If self was created using Weak::new, this will return 0.

Gets the number of Weak pointers pointing to this allocation.

If no strong pointers remain, this will return zero.

Returns true if the two Weaks point to the same allocation (similar to ptr::eq), or if both don't point to any allocation (because they were created with Weak::new()).

Notes

Since this compares pointers it means that Weak::new() will equal each other, even though they don't point to any allocation.

Examples

use std::rc::Rc;

let first_rc = Rc::new(5);
let first = Rc::downgrade(&first_rc);
let second = Rc::downgrade(&first_rc);

assert!(first.ptr_eq(&second));

let third_rc = Rc::new(5);
let third = Rc::downgrade(&third_rc);

assert!(!first.ptr_eq(&third));

Comparing Weak::new.

use std::rc::{Rc, Weak};

let first = Weak::new();
let second = Weak::new();
assert!(first.ptr_eq(&second));

let third_rc = Rc::new(());
let third = Rc::downgrade(&third_rc);
assert!(!first.ptr_eq(&third));