UniqueRc in std::rc - Rust (original) (raw)

pub struct UniqueRc<T, A = Global>

where
    A: Allocator,
    T: ?Sized,

{ /* private fields */ }

🔬This is a nightly-only experimental API. (unique_rc_arc #112566)

Expand description

A uniquely owned Rc.

This represents an Rc that is known to be uniquely owned – that is, have exactly one strong reference. Multiple weak pointers can be created, but attempts to upgrade those to strong references will fail unless the UniqueRc they point to has been converted into a regular Rc.

Because they are uniquely owned, the contents of a UniqueRc can be freely mutated. A common use case is to have an object be mutable during its initialization phase but then have it become immutable and converted to a normal Rc.

This can be used as a flexible way to create cyclic data structures, as in the example below.

#![feature(unique_rc_arc)]
use std::rc::{Rc, Weak, UniqueRc};

struct Gadget {
    #[allow(dead_code)]
    me: Weak<Gadget>,
}

fn create_gadget() -> Option<Rc<Gadget>> {
    let mut rc = UniqueRc::new(Gadget {
        me: Weak::new(),
    });
    rc.me = UniqueRc::downgrade(&rc);
    Some(UniqueRc::into_rc(rc))
}

create_gadget().unwrap();

An advantage of using UniqueRc over Rc::new_cyclic to build cyclic data structures is thatRc::new_cyclic’s data_fn parameter cannot be async or return a Result. As shown in the previous example, UniqueRc allows for more flexibility in the construction of cyclic data, including fallible or async constructors.

🔬This is a nightly-only experimental API. (unique_rc_arc #112566)

Creates a new UniqueRc.

Weak references to this UniqueRc can be created with UniqueRc::downgrade. Upgrading these weak references will fail before the UniqueRc has been converted into an Rc. After converting the UniqueRc into an Rc, any weak references created beforehand will point to the new Rc.

🔬This is a nightly-only experimental API. (unique_rc_arc #112566)

Creates a new UniqueRc in the provided allocator.

Weak references to this UniqueRc can be created with UniqueRc::downgrade. Upgrading these weak references will fail before the UniqueRc has been converted into an Rc. After converting the UniqueRc into an Rc, any weak references created beforehand will point to the new Rc.

🔬This is a nightly-only experimental API. (unique_rc_arc #112566)

Converts the UniqueRc into a regular Rc.

This consumes the UniqueRc and returns a regular Rc that contains the value that is passed to into_rc.

Any weak references created before this method is called can now be upgraded to strong references.

🔬This is a nightly-only experimental API. (unique_rc_arc #112566)

Creates a new weak reference to the UniqueRc.

Attempting to upgrade this weak reference will fail before the UniqueRc has been converted to a Rc using UniqueRc::into_rc.

Available on Windows only.

Converts this type into a mutable reference of the (usually inferred) input type.

Converts this type into a shared reference of the (usually inferred) input type.

Available on Windows only.

The resulting type after dereferencing.

Dereferences the value.

Mutably dereferences the value.

Comparison for two UniqueRcs.

The two are compared by calling cmp() on their inner values.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;
use std::cmp::Ordering;

let five = UniqueRc::new(5);

assert_eq!(Ordering::Less, five.cmp(&UniqueRc::new(6)));

1.21.0 · Source §

Compares and returns the maximum of two values. Read more

1.21.0 · Source §

Compares and returns the minimum of two values. Read more

1.50.0 · Source §

Restrict a value to a certain interval. Read more

Equality for two UniqueRcs.

Two UniqueRcs are equal if their inner values are equal.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;

let five = UniqueRc::new(5);

assert!(five == UniqueRc::new(5));

Inequality for two UniqueRcs.

Two UniqueRcs are not equal if their inner values are not equal.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;

let five = UniqueRc::new(5);

assert!(five != UniqueRc::new(6));

Partial comparison for two UniqueRcs.

The two are compared by calling partial_cmp() on their inner values.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;
use std::cmp::Ordering;

let five = UniqueRc::new(5);

assert_eq!(Some(Ordering::Less), five.partial_cmp(&UniqueRc::new(6)));

Less-than comparison for two UniqueRcs.

The two are compared by calling < on their inner values.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;

let five = UniqueRc::new(5);

assert!(five < UniqueRc::new(6));

‘Less than or equal to’ comparison for two UniqueRcs.

The two are compared by calling <= on their inner values.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;

let five = UniqueRc::new(5);

assert!(five <= UniqueRc::new(5));

Greater-than comparison for two UniqueRcs.

The two are compared by calling > on their inner values.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;

let five = UniqueRc::new(5);

assert!(five > UniqueRc::new(4));

‘Greater than or equal to’ comparison for two UniqueRcs.

The two are compared by calling >= on their inner values.

§Examples

#![feature(unique_rc_arc)]
use std::rc::UniqueRc;

let five = UniqueRc::new(5);

assert!(five >= UniqueRc::new(5));