pub struct UniqueRc<T> {
    ptr: NonNull<RcBox<T>>,
    phantom: PhantomData<RcBox<T>>,
}
🔬This is a nightly-only experimental API. (unique_rc_arc)
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 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.

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§ptr: NonNull<RcBox<T>>
🔬This is a nightly-only experimental API. (unique_rc_arc)
§phantom: PhantomData<RcBox<T>>
🔬This is a nightly-only experimental API. (unique_rc_arc)

Implementations§

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impl<T> UniqueRc<T>

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pub fn new(value: T) -> UniqueRc<T>

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

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.

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pub fn downgrade(this: &UniqueRc<T>) -> Weak<T>

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

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.

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pub fn into_rc(this: UniqueRc<T>) -> Rc<T>

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

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.

Trait Implementations§

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impl<T> Debug for UniqueRc<T>
where T: Debug,

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

Formats the value using the given formatter. Read more
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impl<T> DerefMut for UniqueRc<T>

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

Mutably dereferences the value.
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impl<T> Drop for UniqueRc<T>

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fn drop(&mut self)

Executes the destructor for this type. Read more
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impl<T> Deref for UniqueRc<T>

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type Target = T

The resulting type after dereferencing.
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fn deref(&self) -> &T

Dereferences the value.

Auto Trait Implementations§

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impl<T> !RefUnwindSafe for UniqueRc<T>

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impl<T> !Send for UniqueRc<T>

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impl<T> !Sync for UniqueRc<T>

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impl<T> Unpin for UniqueRc<T>
where T: Unpin,

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impl<T> !UnwindSafe for UniqueRc<T>

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<U> As for U

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fn as_<T>(self) -> T
where T: CastFrom<U>,

Casts self to type T. The semantics of numeric casting with the as operator are followed, so <T as As>::as_::<U> can be used in the same way as T as U for numeric conversions. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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

Mutably borrows from an owned value. Read more
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impl<T> Downcast for T
where T: Any,

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fn into_any(self: Box<T>) -> Box<dyn Any>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait.
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fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>

Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait.
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fn as_any(&self) -> &(dyn Any + 'static)

Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
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fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

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

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impl<T> Pointable for T

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const ALIGN: usize = _

The alignment of pointer.
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type Init = T

The type for initializers.
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unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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impl<T> Same for T

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type Output = T

Should always be Self
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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fn vzip(self) -> V