# Struct std::rc::Rc [−] [src]

    pub struct Rc<T> where T: ?Sized {
        // some fields omitted
    }

A reference-counted pointer type over an immutable value.

See the module level documentation for more details.

## Methods

### `impl<T> Rc<T>`

#### `fn new(value: T) -> Rc<T>`

Constructs a new `Rc<T>`.

# Examples

fn main() { use std::rc::Rc; let five = Rc::new(5); }

    use std::rc::Rc;

    let five = Rc::new(5);

#### `fn try_unwrap(this: Rc<T>) -> Result<T, Rc<T>>`

Unwraps the contained value if the `Rc<T>` has only one strong reference. This will succeed even if there are outstanding weak references.

Otherwise, an `Err` is returned with the same `Rc<T>`.

# Examples

fn main() { use std::rc::Rc; let x = Rc::new(3); assert_eq!(Rc::try_unwrap(x), Ok(3)); let x = Rc::new(4); let _y = x.clone(); assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4))); }

    use std::rc::Rc;

    let x = Rc::new(3);
    assert_eq!(Rc::try_unwrap(x), Ok(3));

    let x = Rc::new(4);
    let _y = x.clone();
    assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4)));

#### `fn would_unwrap(this: &Rc<T>) -> bool`

Unstable (`rc_would_unwrap` #28356)

: just added for niche usecase

Checks if `Rc::try_unwrap` would return `Ok`.

### `impl<T> Rc<T> where T: ?Sized`

#### `fn downgrade(this: &Rc<T>) -> Weak<T>`

Downgrades the `Rc<T>` to a `Weak<T>` reference.

# Examples

fn main() { use std::rc::Rc; let five = Rc::new(5); let weak_five = Rc::downgrade(&five); }

    use std::rc::Rc;

    let five = Rc::new(5);

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

#### `fn weak_count(this: &Rc<T>) -> usize`

Unstable (`rc_counts` #28356)

: not clearly useful

Get the number of weak references to this value.

#### `fn strong_count(this: &Rc<T>) -> usize`

Unstable (`rc_counts` #28356)

: not clearly useful

Get the number of strong references to this value.

#### `fn is_unique(this: &Rc<T>) -> bool`

Unstable (`rc_counts` #28356)

: uniqueness has unclear meaning

Returns true if there are no other `Rc` or `Weak<T>` values that share the same inner value.

# Examples

#![feature(rc_counts)] fn main() { use std::rc::Rc; let five = Rc::new(5); assert!(Rc::is_unique(&five)); }

    #![feature(rc_counts)]

    use std::rc::Rc;

    let five = Rc::new(5);

    assert!(Rc::is_unique(&five));

#### `fn get_mut(this: &mut Rc<T>) -> Option<&mut T>`

Returns a mutable reference to the contained value if the `Rc<T>` has one strong reference and no weak references.

Returns `None` if the `Rc<T>` is not unique.

# Examples

fn main() { use std::rc::Rc; let mut x = Rc::new(3); *Rc::get_mut(&mut x).unwrap() = 4; assert_eq!(*x, 4); let _y = x.clone(); assert!(Rc::get_mut(&mut x).is_none()); }

    use std::rc::Rc;

    let mut x = Rc::new(3);
    *Rc::get_mut(&mut x).unwrap() = 4;
    assert_eq!(*x, 4);

    let _y = x.clone();
    assert!(Rc::get_mut(&mut x).is_none());

### `impl<T> Rc<T> where T: Clone`

#### `fn make_mut(this: &mut Rc<T>) -> &mut T`

Make a mutable reference into the given `Rc<T>` by cloning the inner data if the `Rc<T>` doesn't have one strong reference and no weak references.

This is also referred to as a copy-on-write.

# Examples

fn main() { use std::rc::Rc; let mut data = Rc::new(5); *Rc::make_mut(&mut data) += 1; // Won't clone anything let mut other_data = data.clone(); // Won't clone inner data *Rc::make_mut(&mut data) += 1; // Clones inner data *Rc::make_mut(&mut data) += 1; // Won't clone anything *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything // Note: data and other_data now point to different numbers assert_eq!(*data, 8); assert_eq!(*other_data, 12); }

    use std::rc::Rc;

    let mut data = Rc::new(5);

    *Rc::make_mut(&mut data) += 1;             // Won't clone anything
    let mut other_data = data.clone(); // Won't clone inner data
    *Rc::make_mut(&mut data) += 1;             // Clones inner data
    *Rc::make_mut(&mut data) += 1;             // Won't clone anything
    *Rc::make_mut(&mut other_data) *= 2;       // Won't clone anything

    // Note: data and other_data now point to different numbers
    assert_eq!(*data, 8);
    assert_eq!(*other_data, 12);

## Trait Implementations

### `impl<T> !Send for Rc<T> where T: ?Sized`

### `impl<T> !Sync for Rc<T> where T: ?Sized`

### `impl<T, U> CoerceUnsized<Rc<U>> for Rc<T> where U: ?Sized, T: Unsize<U> + ?Sized`

### `impl<T> Deref for Rc<T> where T: ?Sized`

#### `type Target = T`

#### `fn deref(&self) -> &T`

### `impl<T> Drop for Rc<T> where T: ?Sized`

#### `fn drop(&mut self)`

### `impl<T> Clone for Rc<T> where T: ?Sized`

#### `fn clone(&self) -> Rc<T>`

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

### `impl<T> Default for Rc<T> where T: Default`

#### `fn default() -> Rc<T>`

### `impl<T> PartialEq<Rc<T>> for Rc<T> where T: PartialEq<T> + ?Sized`

#### `fn eq(&self, other: &Rc<T>) -> bool`

#### `fn ne(&self, other: &Rc<T>) -> bool`

### `impl<T> Eq for Rc<T> where T: Eq + ?Sized`

### `impl<T> PartialOrd<Rc<T>> for Rc<T> where T: PartialOrd<T> + ?Sized`

#### `fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering>`

#### `fn lt(&self, other: &Rc<T>) -> bool`

#### `fn le(&self, other: &Rc<T>) -> bool`

#### `fn gt(&self, other: &Rc<T>) -> bool`

#### `fn ge(&self, other: &Rc<T>) -> bool`

### `impl<T> Ord for Rc<T> where T: Ord + ?Sized`

#### `fn cmp(&self, other: &Rc<T>) -> Ordering`

### `impl<T> Hash for Rc<T> where T: Hash + ?Sized`

#### `fn hash<H>(&self, state: &mut H) where H: Hasher`

#### `fn hash_slice<H>(data: &[Self], state: &mut H) where H: Hasher`

### `impl<T> Display for Rc<T> where T: Display + ?Sized`

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

### `impl<T> Debug for Rc<T> where T: Debug + ?Sized`

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

### `impl<T> Pointer for Rc<T>`

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

### `impl<T> From<T> for Rc<T>`

#### `fn from(t: T) -> Rc<T>`

### `impl<T> Borrow<T> for Rc<T> where T: ?Sized`

#### `fn borrow(&self) -> &T`

### `impl<T> AsRef<T> for Rc<T> where T: ?Sized`

#### `fn as_ref(&self) -> &T`

### `impl<T: RefRecoverSafe + ?Sized> RecoverSafe for Rc<T>`

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