pub struct Rc<T> where
T: ?Sized, { /* private fields */ }
Expand description
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
sourceimpl<T> Rc<T>
impl<T> Rc<T>
1.60.0 · sourcepub fn new_cyclic<F>(data_fn: F) -> Rc<T> where
F: FnOnce(&Weak<T>) -> T,
pub fn new_cyclic<F>(data_fn: F) -> Rc<T> where
F: FnOnce(&Weak<T>) -> T,
Constructs a new Rc<T>
while giving you a Weak<T>
to the allocation,
to allow you to construct a T
which holds a weak pointer to itself.
Generally, a structure circularly referencing itself, either directly or
indirectly, should not hold a strong reference to itself to prevent a memory leak.
Using this function, you get access to the weak pointer during the
initialization of T
, before the Rc<T>
is created, such that you can
clone and store it inside the T
.
new_cyclic
first allocates the managed allocation for the Rc<T>
,
then calls your closure, giving it a Weak<T>
to this allocation,
and only afterwards completes the construction of the Rc<T>
by placing
the T
returned from your closure into the allocation.
Since the new Rc<T>
is not fully-constructed until Rc<T>::new_cyclic
returns, calling upgrade
on the weak reference inside your closure will
fail and result in a None
value.
Panics
If data_fn
panics, the panic is propagated to the caller, and the
temporary Weak<T>
is dropped normally.
Examples
use std::rc::{Rc, Weak};
struct Gadget {
me: Weak<Gadget>,
}
impl Gadget {
/// Construct a reference counted Gadget.
fn new() -> Rc<Self> {
// `me` is a `Weak<Gadget>` pointing at the new allocation of the
// `Rc` we're constructing.
Rc::new_cyclic(|me| {
// Create the actual struct here.
Gadget { me: me.clone() }
})
}
/// Return a reference counted pointer to Self.
fn me(&self) -> Rc<Self> {
self.me.upgrade().unwrap()
}
}
Runsourcepub fn new_uninit() -> Rc<MaybeUninit<T>>
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();
// Deferred initialization:
Rc::get_mut(&mut five).unwrap().write(5);
let five = unsafe { five.assume_init() };
assert_eq!(*five, 5)
Runsourcepub fn new_zeroed() -> Rc<MaybeUninit<T>>
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)
Runsourcepub fn try_new(value: T) -> Result<Rc<T>, AllocError>
pub fn try_new(value: T) -> Result<Rc<T>, AllocError>
sourcepub fn try_new_uninit() -> Result<Rc<MaybeUninit<T>>, AllocError>
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()?;
// Deferred initialization:
Rc::get_mut(&mut five).unwrap().write(5);
let five = unsafe { five.assume_init() };
assert_eq!(*five, 5);
Runsourcepub fn try_new_zeroed() -> Result<Rc<MaybeUninit<T>>, AllocError>
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);
Run1.33.0 · sourcepub fn pin(value: T) -> Pin<Rc<T>>ⓘNotable traits for Pin<P>impl<P> Future for Pin<P> where
P: DerefMut,
<P as Deref>::Target: Future, type Output = <<P as Deref>::Target as Future>::Output;
pub fn pin(value: T) -> Pin<Rc<T>>ⓘNotable traits for Pin<P>impl<P> Future for Pin<P> where
P: DerefMut,
<P as Deref>::Target: Future, type Output = <<P as Deref>::Target as Future>::Output;
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.
1.4.0 · sourcepub fn try_unwrap(this: Rc<T>) -> Result<T, Rc<T>>
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);
Runsourceimpl<T> Rc<[T]>
impl<T> Rc<[T]>
sourcepub fn new_uninit_slice(len: usize) -> Rc<[MaybeUninit<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);
// Deferred initialization:
let data = Rc::get_mut(&mut values).unwrap();
data[0].write(1);
data[1].write(2);
data[2].write(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [1, 2, 3])
Runsourcepub fn new_zeroed_slice(len: usize) -> Rc<[MaybeUninit<T>]>
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])
Runsourceimpl<T> Rc<MaybeUninit<T>>
impl<T> Rc<MaybeUninit<T>>
sourcepub unsafe fn assume_init(self) -> Rc<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();
// Deferred initialization:
Rc::get_mut(&mut five).unwrap().write(5);
let five = unsafe { five.assume_init() };
assert_eq!(*five, 5)
Runsourceimpl<T> Rc<[MaybeUninit<T>]>
impl<T> Rc<[MaybeUninit<T>]>
sourcepub unsafe fn assume_init(self) -> Rc<[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);
// Deferred initialization:
let data = Rc::get_mut(&mut values).unwrap();
data[0].write(1);
data[1].write(2);
data[2].write(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [1, 2, 3])
Runsourceimpl<T> Rc<T> where
T: ?Sized,
impl<T> Rc<T> where
T: ?Sized,
1.17.0 · sourcepub fn into_raw(this: Rc<T>) -> *const T
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");
Run1.45.0 · sourcepub fn as_ptr(this: &Rc<T>) -> *const T
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");
Run1.17.0 · sourcepub unsafe fn from_raw(ptr: *const T) -> Rc<T>
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!
Run1.15.0 · sourcepub fn weak_count(this: &Rc<T>) -> usize
pub fn weak_count(this: &Rc<T>) -> usize
1.15.0 · sourcepub fn strong_count(this: &Rc<T>) -> usize
pub fn strong_count(this: &Rc<T>) -> usize
1.53.0 · sourcepub unsafe fn increment_strong_count(ptr: *const T)
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));
}
Run1.53.0 · sourcepub unsafe fn decrement_strong_count(ptr: *const T)
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));
}
Run1.4.0 · sourcepub fn get_mut(this: &mut Rc<T>) -> Option<&mut T>
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());
Runsourcepub unsafe fn get_mut_unchecked(this: &mut Rc<T>) -> &mut T
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");
Runsourceimpl<T> Rc<T> where
T: Clone,
impl<T> Rc<T> where
T: Clone,
1.4.0 · sourcepub fn make_mut(this: &mut Rc<T>) -> &mut T
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);
RunWeak
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());
Runsourcepub fn unwrap_or_clone(this: Rc<T>) -> T
pub fn unwrap_or_clone(this: Rc<T>) -> T
If we have the only reference to T
then unwrap it. Otherwise, clone T
and return the
clone.
Assuming rc_t
is of type Rc<T>
, this function is functionally equivalent to
(*rc_t).clone()
, but will avoid cloning the inner value where possible.
Examples
#![feature(arc_unwrap_or_clone)]
let inner = String::from("test");
let ptr = inner.as_ptr();
let rc = Rc::new(inner);
let inner = Rc::unwrap_or_clone(rc);
// The inner value was not cloned
assert!(ptr::eq(ptr, inner.as_ptr()));
let rc = Rc::new(inner);
let rc2 = rc.clone();
let inner = Rc::unwrap_or_clone(rc);
// Because there were 2 references, we had to clone the inner value.
assert!(!ptr::eq(ptr, inner.as_ptr()));
// `rc2` is the last reference, so when we unwrap it we get back
// the original `String`.
let inner = Rc::unwrap_or_clone(rc2);
assert!(ptr::eq(ptr, inner.as_ptr()));
Runsourceimpl Rc<dyn Any + 'static>
impl Rc<dyn Any + 'static>
1.29.0 · sourcepub fn downcast<T>(self) -> Result<Rc<T>, Rc<dyn Any + 'static>> where
T: Any,
pub fn downcast<T>(self) -> Result<Rc<T>, Rc<dyn Any + 'static>> where
T: Any,
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));
Runsourcepub unsafe fn downcast_unchecked<T>(self) -> Rc<T> where
T: Any,
pub unsafe fn downcast_unchecked<T>(self) -> Rc<T> where
T: Any,
Downcasts the Rc<dyn Any>
to a concrete type.
For a safe alternative see downcast
.
Examples
#![feature(downcast_unchecked)]
use std::any::Any;
use std::rc::Rc;
let x: Rc<dyn Any> = Rc::new(1_usize);
unsafe {
assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}
RunSafety
The contained value must be of type T
. Calling this method
with the incorrect type is undefined behavior.
Trait Implementations
sourceimpl<T> Clone for Rc<T> where
T: ?Sized,
impl<T> Clone for Rc<T> where
T: ?Sized,
sourceimpl<T> Drop for Rc<T> where
T: ?Sized,
impl<T> Drop for Rc<T> where
T: ?Sized,
sourcefn drop(&mut self)
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!"
Run1.45.0 · sourceimpl<'a, B> From<Cow<'a, B>> for Rc<B> where
B: ToOwned + ?Sized,
Rc<B>: From<&'a B>,
Rc<B>: From<<B as ToOwned>::Owned>,
impl<'a, B> From<Cow<'a, B>> for Rc<B> where
B: ToOwned + ?Sized,
Rc<B>: From<&'a B>,
Rc<B>: From<<B as ToOwned>::Owned>,
1.37.0 · sourceimpl<T> FromIterator<T> for Rc<[T]>
impl<T> FromIterator<T> for Rc<[T]>
sourcefn from_iter<I>(iter: I) -> Rc<[T]> where
I: IntoIterator<Item = T>,
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();
Runthis 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.
RunThis 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.
Runsourceimpl<T> Ord for Rc<T> where
T: Ord + ?Sized,
impl<T> Ord for Rc<T> where
T: Ord + ?Sized,
sourceimpl<T> PartialEq<Rc<T>> for Rc<T> where
T: PartialEq<T> + ?Sized,
impl<T> PartialEq<Rc<T>> for Rc<T> where
T: PartialEq<T> + ?Sized,
sourcefn eq(&self, other: &Rc<T>) -> bool
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));
Runsourceimpl<T> PartialOrd<Rc<T>> for Rc<T> where
T: PartialOrd<T> + ?Sized,
impl<T> PartialOrd<Rc<T>> for Rc<T> where
T: PartialOrd<T> + ?Sized,
impl<T, U> CoerceUnsized<Rc<U>> for Rc<T> where
T: Unsize<U> + ?Sized,
U: ?Sized,
impl<T, U> DispatchFromDyn<Rc<U>> for Rc<T> where
T: Unsize<U> + ?Sized,
U: ?Sized,
impl<T> Eq for Rc<T> where
T: Eq + ?Sized,
impl<T> RefUnwindSafe for Rc<T> where
T: RefUnwindSafe + ?Sized,
impl<T> !Send for Rc<T> where
T: ?Sized,
impl<T> !Sync for Rc<T> where
T: ?Sized,
impl<T> Unpin for Rc<T> where
T: ?Sized,
impl<T> UnwindSafe for Rc<T> where
T: RefUnwindSafe + ?Sized,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more