Struct std::rc::Rc

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

A single-threaded reference-counting pointer.

See the module-level documentation for more details.

The inherent methods of Rc are all associated functions, which means that you have to call them as e.g. Rc::get_mut(&value) instead of value.get_mut(). This avoids conflicts with methods of the inner type T.

Methods

impl<T> Rc<T>

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

Constructs a new Rc<T>.

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

Returns the contained value, if the Rc has exactly one strong reference.

Otherwise, an Err is returned with the same Rc that was passed in.

This will succeed even if there are outstanding weak references.

Examples

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).unwrap_err(), 4);

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

Deprecated since 1.15.0

: too niche; use strong_count instead

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

just added for niche usecase

Checks whether Rc::try_unwrap would return Ok.

fn into_raw(this: Rc<T>) -> *mut T

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

Consumes the Rc, returning the wrapped pointer.

To avoid a memory leak the pointer must be converted back to an Rc using Rc::from_raw.

Examples

#![feature(rc_raw)]

use std::rc::Rc;

let x = Rc::new(10);
let x_ptr = Rc::into_raw(x);
assert_eq!(unsafe { *x_ptr }, 10);

unsafe fn from_raw(ptr: *mut T) -> Rc<T>

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

Constructs an Rc from a raw pointer.

The raw pointer must have been previously returned by a call to a Rc::into_raw.

This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.

Examples

#![feature(rc_raw)]

use std::rc::Rc;

let x = Rc::new(10);
let x_ptr = Rc::into_raw(x);

unsafe {
    // Convert back to an `Rc` to prevent leak.
    let x = Rc::from_raw(x_ptr);
    assert_eq!(*x, 10);

    // Further calls to `Rc::from_raw(x_ptr)` would be memory unsafe.
}

// The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!

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

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

Creates a new Weak pointer to this value.

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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

Gets the number of Weak pointers to this value.

Examples

use std::rc::Rc;

let five = Rc::new(5);
let _weak_five = Rc::downgrade(&five);

assert_eq!(1, Rc::weak_count(&five));

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

Gets the number of strong (Rc) pointers to this value.

Examples

use std::rc::Rc;

let five = Rc::new(5);
let _also_five = five.clone();

assert_eq!(2, Rc::strong_count(&five));

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

Deprecated since 1.15.0

: too niche; use strong_count and weak_count instead

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

uniqueness has unclear meaning

Returns true if there are no other Rc or Weak pointers to this inner value.

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

Returns a mutable reference to the inner value, if there are no other Rc or Weak pointers to the same value.

Returns None otherwise, because it is not safe to mutate a shared value.

See also make_mut, which will clone the inner value when it's shared.

Examples

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());

fn ptr_eq(this: &Rc<T>, other: &Rc<T>) -> bool

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

newly added

Returns true if the two Rcs point to the same value (not just values that compare as equal).

Examples

#![feature(ptr_eq)]

use std::rc::Rc;

let five = Rc::new(5);
let same_five = five.clone();
let other_five = Rc::new(5);

assert!(Rc::ptr_eq(&five, &same_five));
assert!(!Rc::ptr_eq(&five, &other_five));

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

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

Makes a mutable reference into the given Rc.

If there are other Rc or Weak pointers to the same value, then make_mut will invoke clone on the inner value to ensure unique ownership. This is also referred to as clone-on-write.

See also get_mut, which will fail rather than cloning.

Examples

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

// Now `data` and `other_data` point to different values.
assert_eq!(*data, 8);
assert_eq!(*other_data, 12);

Trait Implementations

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

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

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

fn default() -> Rc<T>

Creates a new Rc<T>, with the Default value for T.

Examples

use std::rc::Rc;

let x: Rc<i32> = Default::default();
assert_eq!(*x, 0);

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

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

Feeds this value into the state given, updating the hasher as necessary.

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

Feeds a slice of this type into the state provided.

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

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

Equality for two Rcs.

Two Rcs are equal if their inner values are equal.

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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

Inequality for two Rcs.

Two Rcs are unequal if their inner values are unequal.

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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

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

Partial comparison for two Rcs.

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

Examples

use std::rc::Rc;
use std::cmp::Ordering;

let five = Rc::new(5);

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

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

Less-than comparison for two Rcs.

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

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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

'Less than or equal to' comparison for two Rcs.

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

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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

Greater-than comparison for two Rcs.

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

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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

'Greater than or equal to' comparison for two Rcs.

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

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

impl<T> From<T> for Rc<T>

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

Performs the conversion.

impl<T> Pointer for Rc<T> where T: ?Sized

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

Formats the value using the given formatter.

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

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

Makes a clone of the Rc pointer.

This creates another pointer to the same inner value, increasing the strong reference count.

Examples

use std::rc::Rc;

let five = Rc::new(5);

five.clone();

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

Performs copy-assignment from source.

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

type Target = T

The resulting type after dereferencing

fn deref(&self) -> &T

The method called to dereference a value

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

fn drop(&mut self)

Drops the Rc.

This will decrement the strong reference count. If the strong reference count reaches zero then the only other references (if any) are Weak, so we drop the inner value.

Examples

use std::rc::Rc;

struct Foo;

impl Drop for Foo {
    fn drop(&mut self) {
        println!("dropped!");
    }
}

let foo  = Rc::new(Foo);
let foo2 = foo.clone();

drop(foo);    // Doesn't print anything
drop(foo2);   // Prints "dropped!"

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

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

fn as_ref(&self) -> &T

Performs the conversion.

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

fn borrow(&self) -> &T

Immutably borrows from an owned value.

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

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

Formats the value using the given formatter.

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

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

Comparison for two Rcs.

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

Examples

use std::rc::Rc;
use std::cmp::Ordering;

let five = Rc::new(5);

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

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

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

Formats the value using the given formatter.

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