Struct WeakEq 

pub struct WeakEq<T: Send + Sync>(pub Weak<T>);

An std::sync::Weak value that implements equality by pointer comparison.

This type allows external types that are only Send + Sync to become a full VarValue to be allowed as a variable value.

Tuple Fields

0: Weak<T>

Implementations

impl<T: Debug + Send + Sync> WeakEq<T>

pub fn upgrade(&self) -> Option<ArcEq<T>>

Attempt to upgrade to ArcEq<T>.

impl<T: Send + Sync> WeakEq<T>

pub const fn new() -> Self

New without alloc.

Methods from Deref<Target = Weak<T>>

pub fn allocator(&self) -> &A

🔬This is a nightly-only experimental API. (allocator_api)

Returns a reference to the underlying allocator.

pub fn as_ptr(&self) -> *const T

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::sync::Arc;
use std::ptr;

let strong = Arc::new("hello".to_owned());
let weak = Arc::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 behavior.
// assert_eq!("hello", unsafe { &*weak.as_ptr() });

pub fn upgrade(&self) -> Option<Arc<T, A>>

where A: Clone,

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

Returns None if the inner 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());

pub fn strong_count(&self) -> usize

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

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

pub fn weak_count(&self) -> usize

Gets an approximation of the number of Weak pointers pointing to this allocation.

If self was created using Weak::new, or if there are no remaining strong pointers, this will return 0.

Accuracy

Due to implementation details, the returned value can be off by 1 in either direction when other threads are manipulating any Arcs or Weaks pointing to the same allocation.

pub fn ptr_eq(&self, other: &Weak<T, A>) -> bool

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()). However, this function ignores the metadata of dyn Trait pointers.

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::sync::Arc;

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

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

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

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

Comparing Weak::new.

use std::sync::{Arc, Weak};

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

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

Trait Implementations

impl<T: Send + Sync> Clone for WeakEq<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Send + Sync> Debug for WeakEq<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: Send + Sync> Default for WeakEq<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T: Send + Sync> Deref for WeakEq<T>

type Target = Weak<T>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<T: Send + Sync> PartialEq for WeakEq<T>

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: Send + Sync> Eq for WeakEq<T>