Struct UniqueRc

struct UniqueRc<T: ?Sized, A: Allocator = crate::alloc::Global> { ... }

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 that Rc::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.

Implementations

impl<T> UniqueRc<T>

fn new(value: T) -> Self

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.

fn map<U, impl FnOnce(T) -> U: FnOnce(T) -> U>(this: Self, f: impl FnOnce(T) -> U) -> UniqueRc<U>

Maps the value in a UniqueRc, reusing the allocation if possible.

f is called on a reference to the value in the UniqueRc, and the result is returned, also in a UniqueRc.

Note: this is an associated function, which means that you have to call it as UniqueRc::map(u, f) instead of u.map(f). This is so that there is no conflict with a method on the inner type.

Examples

#![feature(smart_pointer_try_map)]
#![feature(unique_rc_arc)]

use std::rc::UniqueRc;

let r = UniqueRc::new(7);
let new = UniqueRc::map(r, |i| i + 7);
assert_eq!(*new, 14);

fn try_map<R, impl FnOnce(T) -> R: FnOnce(T) -> R>(this: Self, f: impl FnOnce(T) -> R) -> <<R as >::Residual as Residual<UniqueRc<<R as >::Output>>>::TryType
where
    R: Try,
    <R as >::Residual: Residual<UniqueRc<<R as >::Output>>

Attempts to map the value in a UniqueRc, reusing the allocation if possible.

f is called on a reference to the value in the UniqueRc, and if the operation succeeds, the result is returned, also in a UniqueRc.

Note: this is an associated function, which means that you have to call it as UniqueRc::try_map(u, f) instead of u.try_map(f). This is so that there is no conflict with a method on the inner type.

Examples

#![feature(smart_pointer_try_map)]
#![feature(unique_rc_arc)]

use std::rc::UniqueRc;

let b = UniqueRc::new(7);
let new = UniqueRc::try_map(b, u32::try_from).unwrap();
assert_eq!(*new, 7);

impl<T, A: Allocator> UniqueRc<T, A>

fn new_in(value: T, alloc: A) -> Self

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.

impl<T: ?Sized, A: Allocator + Clone> UniqueRc<T, A>

fn downgrade(this: &Self) -> Weak<T, A>

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.

impl<T: ?Sized, A: Allocator> UniqueRc<T, A>

fn into_rc(this: Self) -> Rc<T, A>

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.

impl<P, T> Receiver for UniqueRc<T, A>

impl<T> Any for UniqueRc<T, A>

fn type_id(self: &Self) -> TypeId

impl<T> Borrow for UniqueRc<T, A>

fn borrow(self: &Self) -> &T

impl<T> BorrowMut for UniqueRc<T, A>

fn borrow_mut(self: &mut Self) -> &mut T

impl<T> From for UniqueRc<T, A>

fn from(t: T) -> T

Returns the argument unchanged.

impl<T> ToString for UniqueRc<T, A>

fn to_string(self: &Self) -> String

impl<T, A = Global> RefUnwindSafe for UniqueRc<T, A>

impl<T, A = Global> UnwindSafe for UniqueRc<T, A>

impl<T, A> Freeze for UniqueRc<T, A>

impl<T, U> Into for UniqueRc<T, A>

fn into(self: Self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

impl<T, U> TryFrom for UniqueRc<T, A>

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto for UniqueRc<T, A>

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>

impl<T: ?Sized + Eq, A: Allocator> Eq for UniqueRc<T, A>

impl<T: ?Sized + Hash, A: Allocator> Hash for UniqueRc<T, A>

fn hash<H: Hasher>(self: &Self, state: &mut H)

impl<T: ?Sized + Ord, A: Allocator> Ord for UniqueRc<T, A>

fn cmp(self: &Self, other: &UniqueRc<T, A>) -> Ordering

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)));

impl<T: ?Sized + PartialEq, A: Allocator> PartialEq for UniqueRc<T, A>

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

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));

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

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));

impl<T: ?Sized + PartialOrd, A: Allocator> PartialOrd for UniqueRc<T, A>

fn partial_cmp(self: &Self, other: &UniqueRc<T, A>) -> Option<Ordering>

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)));

fn lt(self: &Self, other: &UniqueRc<T, A>) -> bool

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));

fn le(self: &Self, other: &UniqueRc<T, A>) -> bool

'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));

fn gt(self: &Self, other: &UniqueRc<T, A>) -> bool

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));

fn ge(self: &Self, other: &UniqueRc<T, A>) -> bool

'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));

impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn for UniqueRc<T>

impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized for UniqueRc<T, A>

impl<T: ?Sized + fmt::Debug, A: Allocator> Debug for UniqueRc<T, A>

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

impl<T: ?Sized + fmt::Display, A: Allocator> Display for UniqueRc<T, A>

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

impl<T: ?Sized, A: Allocator> AsMut for UniqueRc<T, A>

fn as_mut(self: &mut Self) -> &mut T

impl<T: ?Sized, A: Allocator> AsRef for UniqueRc<T, A>

fn as_ref(self: &Self) -> &T

impl<T: ?Sized, A: Allocator> Borrow for UniqueRc<T, A>

fn borrow(self: &Self) -> &T

impl<T: ?Sized, A: Allocator> BorrowMut for UniqueRc<T, A>

fn borrow_mut(self: &mut Self) -> &mut T

impl<T: ?Sized, A: Allocator> Deref for UniqueRc<T, A>

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

impl<T: ?Sized, A: Allocator> DerefMut for UniqueRc<T, A>

fn deref_mut(self: &mut Self) -> &mut T

impl<T: ?Sized, A: Allocator> DerefPure for UniqueRc<T, A>

impl<T: ?Sized, A: Allocator> Drop for UniqueRc<T, A>

fn drop(self: &mut Self)

impl<T: ?Sized, A: Allocator> PinCoerceUnsized for UniqueRc<T, A>

impl<T: ?Sized, A: Allocator> Pointer for UniqueRc<T, A>

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

impl<T: ?Sized, A: Allocator> Send for UniqueRc<T, A>

impl<T: ?Sized, A: Allocator> Sync for UniqueRc<T, A>

impl<T: ?Sized, A: Allocator> Unpin for UniqueRc<T, A>