Struct std::rc::Rc
pub struct Rc<T> where T: ?Sized, { /* fields omitted */ }
A single-threaded reference-counting pointer. ‘Rc’ stands for ‘Reference Counted’.
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(&mut value)
instead of value.get_mut()
. This avoids conflicts with methods of the inner type T
.
Implementations
impl<T> Rc<T>
pub fn new(value: T) -> Rc<T>
Constructs a new Rc<T>
.
Examples
use std::rc::Rc; let five = Rc::new(5);
pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Rc<T>
Constructs a new Rc<T>
using a weak reference to itself. Attempting to upgrade the weak reference before this function returns will result in a None
value. However, the weak reference may be cloned freely and stored for use at a later time.
Examples
#![feature(arc_new_cyclic)] #![allow(dead_code)] use std::rc::{Rc, Weak}; struct Gadget { self_weak: Weak<Self>, // ... more fields } impl Gadget { pub fn new() -> Rc<Self> { Rc::new_cyclic(|self_weak| { Gadget { self_weak: self_weak.clone(), /* ... */ } }) } }
pub fn new_uninit() -> Rc<MaybeUninit<T>>
Constructs a new Rc
with uninitialized contents.
Examples
#![feature(new_uninit)] #![feature(get_mut_unchecked)] use std::rc::Rc; let mut five = Rc::<u32>::new_uninit(); let five = unsafe { // Deferred initialization: Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); five.assume_init() }; assert_eq!(*five, 5)
pub fn new_zeroed() -> Rc<MaybeUninit<T>>
Constructs a new Rc
with uninitialized contents, with the memory being filled with 0
bytes.
See MaybeUninit::zeroed
for examples of correct and incorrect usage of this method.
Examples
#![feature(new_uninit)] use std::rc::Rc; let zero = Rc::<u32>::new_zeroed(); let zero = unsafe { zero.assume_init() }; assert_eq!(*zero, 0)
pub fn try_new(value: T) -> Result<Rc<T>, AllocError>
Constructs a new Rc<T>
, returning an error if the allocation fails
Examples
#![feature(allocator_api)] use std::rc::Rc; let five = Rc::try_new(5);
pub fn try_new_uninit() -> Result<Rc<MaybeUninit<T>>, AllocError>
Constructs a new Rc
with uninitialized contents, returning an error if the allocation fails
Examples
#![feature(allocator_api, new_uninit)] #![feature(get_mut_unchecked)] use std::rc::Rc; let mut five = Rc::<u32>::try_new_uninit()?; let five = unsafe { // Deferred initialization: Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); five.assume_init() }; assert_eq!(*five, 5);
pub fn try_new_zeroed() -> Result<Rc<MaybeUninit<T>>, AllocError>
Constructs a new Rc
with uninitialized contents, with the memory being filled with 0
bytes, returning an error if the allocation fails
See MaybeUninit::zeroed
for examples of correct and incorrect usage of this method.
Examples
#![feature(allocator_api, new_uninit)] use std::rc::Rc; let zero = Rc::<u32>::try_new_zeroed()?; let zero = unsafe { zero.assume_init() }; assert_eq!(*zero, 0);
pub fn pin(value: T) -> Pin<Rc<T>>
impl<P> Future for Pin<P> where P: DerefMut, <P as Deref>::Target: Future, type Output = <<P as Deref>::Target as Future>::Output;
Constructs a new Pin<Rc<T>>
. If T
does not implement Unpin
, then value
will be pinned in memory and unable to be moved.
pub fn try_unwrap(this: Rc<T>) -> Result<T, Rc<T>>
Returns the inner 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 = Rc::clone(&x); assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);
impl<T> Rc<[T]>
pub fn new_uninit_slice(len: usize) -> Rc<[MaybeUninit<T>]>
Constructs a new reference-counted slice with uninitialized contents.
Examples
#![feature(new_uninit)] #![feature(get_mut_unchecked)] use std::rc::Rc; let mut values = Rc::<[u32]>::new_uninit_slice(3); let values = unsafe { // Deferred initialization: Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); values.assume_init() }; assert_eq!(*values, [1, 2, 3])
pub fn new_zeroed_slice(len: usize) -> Rc<[MaybeUninit<T>]>
Constructs a new reference-counted slice with uninitialized contents, with the memory being filled with 0
bytes.
See MaybeUninit::zeroed
for examples of correct and incorrect usage of this method.
Examples
#![feature(new_uninit)] use std::rc::Rc; let values = Rc::<[u32]>::new_zeroed_slice(3); let values = unsafe { values.assume_init() }; assert_eq!(*values, [0, 0, 0])
impl<T> Rc<MaybeUninit<T>>
pub unsafe fn assume_init(self) -> Rc<T>
Converts to Rc<T>
.
Safety
As with MaybeUninit::assume_init
, it is up to the caller to guarantee that the inner value really is in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.
Examples
#![feature(new_uninit)] #![feature(get_mut_unchecked)] use std::rc::Rc; let mut five = Rc::<u32>::new_uninit(); let five = unsafe { // Deferred initialization: Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); five.assume_init() }; assert_eq!(*five, 5)
impl<T> Rc<[MaybeUninit<T>]>
pub unsafe fn assume_init(self) -> Rc<[T]>
Converts to Rc<[T]>
.
Safety
As with MaybeUninit::assume_init
, it is up to the caller to guarantee that the inner value really is in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.
Examples
#![feature(new_uninit)] #![feature(get_mut_unchecked)] use std::rc::Rc; let mut values = Rc::<[u32]>::new_uninit_slice(3); let values = unsafe { // Deferred initialization: Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); values.assume_init() }; assert_eq!(*values, [1, 2, 3])
pub fn into_raw(this: Rc<T>) -> *const T
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
use std::rc::Rc; let x = Rc::new("hello".to_owned()); let x_ptr = Rc::into_raw(x); assert_eq!(unsafe { &*x_ptr }, "hello");
pub fn as_ptr(this: &Rc<T>) -> *const T
Provides a raw pointer to the data.
The counts are not affected in any way and the Rc
is not consumed. The pointer is valid for as long there are strong counts in the Rc
.
Examples
use std::rc::Rc; let x = Rc::new("hello".to_owned()); let y = Rc::clone(&x); let x_ptr = Rc::as_ptr(&x); assert_eq!(x_ptr, Rc::as_ptr(&y)); assert_eq!(unsafe { &*x_ptr }, "hello");
pub unsafe fn from_raw(ptr: *const T) -> Rc<T>
Constructs an Rc<T>
from a raw pointer.
The raw pointer must have been previously returned by a call to Rc<U>::into_raw
where U
must have the same size and alignment as T
. This is trivially true if U
is T
. Note that if U
is not T
but has the same size and alignment, this is basically like transmuting references of different types. See mem::transmute
for more information on what restrictions apply in this case.
The user of from_raw
has to make sure a specific value of T
is only dropped once.
This function is unsafe because improper use may lead to memory unsafety, even if the returned Rc<T>
is never accessed.
Examples
use std::rc::Rc; let x = Rc::new("hello".to_owned()); 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, "hello"); // 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!
pub fn downgrade(this: &Rc<T>) -> Weak<T>
Creates a new Weak
pointer to this allocation.
Examples
use std::rc::Rc; let five = Rc::new(5); let weak_five = Rc::downgrade(&five);
pub fn weak_count(this: &Rc<T>) -> usize
Gets the number of Weak
pointers to this allocation.
Examples
use std::rc::Rc; let five = Rc::new(5); let _weak_five = Rc::downgrade(&five); assert_eq!(1, Rc::weak_count(&five));
pub fn strong_count(this: &Rc<T>) -> usize
Gets the number of strong (Rc
) pointers to this allocation.
Examples
use std::rc::Rc; let five = Rc::new(5); let _also_five = Rc::clone(&five); assert_eq!(2, Rc::strong_count(&five));
pub unsafe fn increment_strong_count(ptr: *const T)
Increments the strong reference count on the Rc<T>
associated with the provided pointer by one.
Safety
The pointer must have been obtained through Rc::into_raw
, and the associated Rc
instance must be valid (i.e. the strong count must be at least 1) for the duration of this method.
Examples
use std::rc::Rc; let five = Rc::new(5); unsafe { let ptr = Rc::into_raw(five); Rc::increment_strong_count(ptr); let five = Rc::from_raw(ptr); assert_eq!(2, Rc::strong_count(&five)); }
pub unsafe fn decrement_strong_count(ptr: *const T)
Decrements the strong reference count on the Rc<T>
associated with the provided pointer by one.
Safety
The pointer must have been obtained through Rc::into_raw
, and the associated Rc
instance must be valid (i.e. the strong count must be at least 1) when invoking this method. This method can be used to release the final Rc
and backing storage, but should not be called after the final Rc
has been released.
Examples
use std::rc::Rc; let five = Rc::new(5); unsafe { let ptr = Rc::into_raw(five); Rc::increment_strong_count(ptr); let five = Rc::from_raw(ptr); assert_eq!(2, Rc::strong_count(&five)); Rc::decrement_strong_count(ptr); assert_eq!(1, Rc::strong_count(&five)); }
pub fn get_mut(this: &mut Rc<T>) -> Option<&mut T>
Returns a mutable reference into the given Rc
, if there are no other Rc
or Weak
pointers to the same allocation.
Returns None
otherwise, because it is not safe to mutate a shared value.
See also make_mut
, which will clone
the inner value when there are other Rc
pointers.
Examples
use std::rc::Rc; let mut x = Rc::new(3); *Rc::get_mut(&mut x).unwrap() = 4; assert_eq!(*x, 4); let _y = Rc::clone(&x); assert!(Rc::get_mut(&mut x).is_none());
pub unsafe fn get_mut_unchecked(this: &mut Rc<T>) -> &mut T
Returns a mutable reference into the given Rc
, without any check.
See also get_mut
, which is safe and does appropriate checks.
Safety
Any other Rc
or Weak
pointers to the same allocation must not be dereferenced for the duration of the returned borrow. This is trivially the case if no such pointers exist, for example immediately after Rc::new
.
Examples
#![feature(get_mut_unchecked)] use std::rc::Rc; let mut x = Rc::new(String::new()); unsafe { Rc::get_mut_unchecked(&mut x).push_str("foo") } assert_eq!(*x, "foo");
pub fn ptr_eq(this: &Rc<T>, other: &Rc<T>) -> bool
Returns true
if the two Rc
s point to the same allocation (in a vein similar to ptr::eq
).
Examples
use std::rc::Rc; let five = Rc::new(5); let same_five = Rc::clone(&five); let other_five = Rc::new(5); assert!(Rc::ptr_eq(&five, &same_five)); assert!(!Rc::ptr_eq(&five, &other_five));
pub fn make_mut(this: &mut Rc<T>) -> &mut T
Makes a mutable reference into the given Rc
.
If there are other Rc
pointers to the same allocation, then make_mut
will clone
the inner value to a new allocation to ensure unique ownership. This is also referred to as clone-on-write.
However, if there are no other Rc
pointers to this allocation, but some Weak
pointers, then the Weak
pointers will be disassociated and the inner value will not be cloned.
See also get_mut
, which will fail rather than cloning the inner value or diassociating Weak
pointers.
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 = Rc::clone(&data); // 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 allocations. assert_eq!(*data, 8); assert_eq!(*other_data, 12);
Weak
pointers will be disassociated:
use std::rc::Rc; let mut data = Rc::new(75); let weak = Rc::downgrade(&data); assert!(75 == *data); assert!(75 == *weak.upgrade().unwrap()); *Rc::make_mut(&mut data) += 1; assert!(76 == *data); assert!(weak.upgrade().is_none());
impl Rc<dyn Any + 'static>
Attempt to downcast the Rc<dyn Any>
to a concrete type.
Examples
use std::any::Any; use std::rc::Rc; fn print_if_string(value: Rc<dyn Any>) { if let Ok(string) = value.downcast::<String>() { println!("String ({}): {}", string.len(), string); } } let my_string = "Hello World".to_string(); print_if_string(Rc::new(my_string)); print_if_string(Rc::new(0i8));
Trait Implementations
pub fn as_ref(&self) -> &T
Performs the conversion.
pub fn clone(&self) -> Rc<T>
Makes a clone of the Rc
pointer.
This creates another pointer to the same allocation, increasing the strong reference count.
Examples
use std::rc::Rc; let five = Rc::new(5); let _ = Rc::clone(&five);
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
pub fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>
Formats the value using the given formatter. Read more
pub 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);
type Target = T
The resulting type after dereferencing.
pub fn deref(&self) -> &T
Dereferences the value.
pub fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>
Formats the value using the given formatter. Read more
pub 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 = Rc::clone(&foo); drop(foo); // Doesn't print anything drop(foo2); // Prints "dropped!"
pub fn from(v: &[T]) -> Rc<[T]>
Allocate a reference-counted slice and fill it by cloning v
’s items.
Example
let original: &[i32] = &[1, 2, 3]; let shared: Rc<[i32]> = Rc::from(original); assert_eq!(&[1, 2, 3], &shared[..]);
impl From<&'_ CStr> for Rc<CStr>
fn from(s: &CStr) -> Rc<CStr>
Performs the conversion.
impl From<&'_ OsStr> for Rc<OsStr>
fn from(s: &OsStr) -> Rc<OsStr>
Performs the conversion.
impl From<&'_ Path> for Rc<Path>
fn from(s: &Path) -> Rc<Path>
impl<'_> From<&'_ str> for Rc<str>
pub fn from(v: &str) -> Rc<str>
Allocate a reference-counted string slice and copy v
into it.
Example
let shared: Rc<str> = Rc::from("statue"); assert_eq!("statue", &shared[..]);
pub fn from(v: Box<T, Global>) -> Rc<T>
Move a boxed object to a new, reference counted, allocation.
Example
let original: Box<i32> = Box::new(1); let shared: Rc<i32> = Rc::from(original); assert_eq!(1, *shared);
impl From<CString> for Rc<CStr>
fn from(s: CString) -> Rc<CStr>
pub fn from(cow: Cow<'a, B>) -> Rc<B>
Create a reference-counted pointer from a clone-on-write pointer by copying its content.
Example
let cow: Cow<str> = Cow::Borrowed("eggplant"); let shared: Rc<str> = Rc::from(cow); assert_eq!("eggplant", &shared[..]);
impl From<OsString> for Rc<OsStr>
fn from(s: OsString) -> Rc<OsStr>
impl From<PathBuf> for Rc<Path>
fn from(s: PathBuf) -> Rc<Path>
impl From<String> for Rc<str>
pub fn from(v: String) -> Rc<str>
Allocate a reference-counted string slice and copy v
into it.
Example
let original: String = "statue".to_owned(); let shared: Rc<str> = Rc::from(original); assert_eq!("statue", &shared[..]);
impl<T> From<T> for Rc<T>
pub fn from(t: T) -> Rc<T>
Converts a generic type T
into an Rc<T>
The conversion allocates on the heap and moves t
from the stack into it.
Example
let x = 5; let rc = Rc::new(5); assert_eq!(Rc::from(x), rc);
impl<T> From<Vec<T, Global>> for Rc<[T]>
pub fn from(v: Vec<T, Global>) -> Rc<[T]>
Allocate a reference-counted slice and move v
’s items into it.
Example
let original: Box<Vec<i32>> = Box::new(vec![1, 2, 3]); let shared: Rc<Vec<i32>> = Rc::from(original); assert_eq!(vec![1, 2, 3], *shared);
impl<T> FromIterator<T> for Rc<[T]>
pub fn from_iter<I>(iter: I) -> Rc<[T]> where
I: IntoIterator<Item = T>,
Takes each element in the Iterator
and collects it into an Rc<[T]>
.
Performance characteristics
The general case
In the general case, collecting into Rc<[T]>
is done by first collecting into a Vec<T>
. That is, when writing the following:
let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();
this behaves as if we wrote:
let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0) .collect::<Vec<_>>() // The first set of allocations happens here. .into(); // A second allocation for `Rc<[T]>` happens here.
This will allocate as many times as needed for constructing the Vec<T>
and then it will allocate once for turning the Vec<T>
into the Rc<[T]>
.
Iterators of known length
When your Iterator
implements TrustedLen
and is of an exact size, a single allocation will be made for the Rc<[T]>
. For example:
let evens: Rc<[u8]> = (0..10).collect(); // Just a single allocation happens here.
pub fn cmp(&self, other: &Rc<T>) -> Ordering
Comparison for two Rc
s.
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)));
fn max(self, other: Self) -> Self
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
Compares and returns the minimum of two values. Read more
fn clamp(self, min: Self, max: Self) -> Self
Restrict a value to a certain interval. Read more
pub fn eq(&self, other: &Rc<T>) -> bool
Equality for two Rc
s.
Two Rc
s are equal if their inner values are equal, even if they are stored in different allocation.
If T
also implements Eq
(implying reflexivity of equality), two Rc
s that point to the same allocation are always equal.
Examples
use std::rc::Rc; let five = Rc::new(5); assert!(five == Rc::new(5));
pub fn ne(&self, other: &Rc<T>) -> bool
Inequality for two Rc
s.
Two Rc
s are unequal if their inner values are unequal.
If T
also implements Eq
(implying reflexivity of equality), two Rc
s that point to the same allocation are never 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,
pub fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering>
Partial comparison for two Rc
s.
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)));
pub fn lt(&self, other: &Rc<T>) -> bool
Less-than comparison for two Rc
s.
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));
pub fn le(&self, other: &Rc<T>) -> bool
‘Less than or equal to’ comparison for two Rc
s.
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));
pub fn gt(&self, other: &Rc<T>) -> bool
Greater-than comparison for two Rc
s.
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));
pub fn ge(&self, other: &Rc<T>) -> bool
‘Greater than or equal to’ comparison for two Rc
s.
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));
pub fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>
Formats the value using the given formatter.
impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]>
type Error = Rc<[T]>
The type returned in the event of a conversion error.
pub fn try_from(
boxed_slice: Rc<[T]>
) -> Result<Rc<[T; N]>, <Rc<[T; N]> as TryFrom<Rc<[T]>>>::Error>
Performs the conversion.
impl<T> UnwindSafe for Rc<T> where
T: RefUnwindSafe + ?Sized,
Auto Trait Implementations
impl<T> !RefUnwindSafe for Rc<T>
Blanket Implementations
impl<T> From<!> for T
pub fn from(t: !) -> T
Performs the conversion.
impl<T> From<T> for T
pub fn from(t: T) -> T
Performs the conversion.
pub fn into(self) -> U
Performs the conversion.
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
Creates owned data from borrowed data, usually by cloning. Read more
pub fn clone_into(&self, target: &mut T)
toowned_clone_into
#41263)recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/rc/struct.Rc.html