Attempts 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));

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);
}

Safety

The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.

Constructs a new Rc<T>.

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

# #![allow(dead_code)]
use std::rc::{Rc, Weak};

struct Gadget {
    me: Weak<Gadget>,
}

impl Gadget {
    /// Constructs 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() }
        })
    }

    /// Returns a reference counted pointer to Self.
    fn me(&self) -> Rc<Self> {
        self.me.upgrade().unwrap()
    }
}

Constructs a new Rc with uninitialized contents.

Examples

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)

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

use std::rc::Rc;

let zero = Rc::<u32>::new_zeroed();
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0)

Constructs a new Rc<T>, returning an error if the allocation fails

Examples

#![feature(allocator_ext)]
use std::rc::Rc;

let five = Rc::try_new(5);
# Ok::<(), std::alloc::AllocError>(())

Constructs a new Rc with uninitialized contents, returning an error if the allocation fails

Examples

#![feature(allocator_ext)]

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);
# Ok::<(), std::alloc::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_ext)]

use std::rc::Rc;

let zero = Rc::<u32>::try_new_zeroed()?;
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0);
# Ok::<(), std::alloc::AllocError>(())

Constructs a new Pin<Rc<T>>. If T does not implement Unpin, then value will be pinned in memory and unable to be moved.

Allocates an RcInner<[T]> with the given length.

Copy elements from slice into newly allocated Rc<[T]>

Unsafe because the caller must either take ownership, bind T: Copy or bind T: TrivialClone.

Constructs an Rc<[T]> from an iterator known to be of a certain size.

Behavior is undefined should the size be wrong.

Constructs a new reference-counted slice with uninitialized contents.

Examples

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])

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

use std::rc::Rc;

let values = Rc::<[u32]>::new_zeroed_slice(3);
let values = unsafe { values.assume_init() };

assert_eq!(*values, [0, 0, 0])

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

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)

Constructs a new Rc in the provided allocator.

Examples

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let five = Rc::new_in(5, System);

Constructs a new Rc with uninitialized contents in the provided allocator.

Examples

#![feature(get_mut_unchecked)]
#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let mut five = Rc::<u32, _>::new_uninit_in(System);

let five = unsafe {
    // Deferred initialization:
    Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);

    five.assume_init()
};

assert_eq!(*five, 5)

Constructs a new Rc with uninitialized contents, with the memory being filled with 0 bytes, in the provided allocator.

See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.

Examples

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let zero = Rc::<u32, _>::new_zeroed_in(System);
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0)

Constructs a new Rc<T, A> in the given allocator while giving you a Weak<T, A> 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, A> is created, such that you can clone and store it inside the T.

new_cyclic_in first allocates the managed allocation for the Rc<T, A>, then calls your closure, giving it a Weak<T, A> to this allocation, and only afterwards completes the construction of the Rc<T, A> by placing the T returned from your closure into the allocation.

Since the new Rc<T, A> is not fully-constructed until Rc<T, A>::new_cyclic_in 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, A>] is dropped normally.

Examples

See new_cyclic.

Constructs a new Rc<T> in the provided allocator, returning an error if the allocation fails

Examples

#![feature(allocator_ext)]
use std::rc::Rc;
use std::alloc::System;

let five = Rc::try_new_in(5, System);
# Ok::<(), std::alloc::AllocError>(())

Constructs a new Rc with uninitialized contents, in the provided allocator, returning an error if the allocation fails

Examples

#![feature(allocator_ext)]
#![feature(get_mut_unchecked)]

use std::rc::Rc;
use std::alloc::System;

let mut five = Rc::<u32, _>::try_new_uninit_in(System)?;

let five = unsafe {
    // Deferred initialization:
    Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);

    five.assume_init()
};

assert_eq!(*five, 5);
# Ok::<(), std::alloc::AllocError>(())

Constructs a new Rc with uninitialized contents, with the memory being filled with 0 bytes, in the provided allocator, returning an error if the allocation fails

See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.

Examples

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let zero = Rc::<u32, _>::try_new_zeroed_in(System)?;
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0);
# Ok::<(), std::alloc::AllocError>(())

Constructs a new Pin<Rc<T>> in the provided allocator. If T does not implement Unpin, then value will be pinned in memory and unable to be moved.

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);

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

Otherwise, None is returned and the Rc is dropped.

This will succeed even if there are outstanding weak references.

If Rc::into_inner is called on every clone of this Rc, it is guaranteed that exactly one of the calls returns the inner value. This means in particular that the inner value is not dropped.

Rc::try_unwrap is conceptually similar to Rc::into_inner. And while they are meant for different use-cases, Rc::into_inner(this) is in fact equivalent to [Rc::try_unwrap](this).[ok]Result::ok. (Note that the same kind of equivalence does not hold true for Arc, due to race conditions that do not apply to Rc!)

Examples

use std::rc::Rc;

let x = Rc::new(3);
assert_eq!(Rc::into_inner(x), Some(3));

let x = Rc::new(4);
let y = Rc::clone(&x);

assert_eq!(Rc::into_inner(y), None);
assert_eq!(Rc::into_inner(x), Some(4));

Maps the value in an Rc, reusing the allocation if possible.

f is called on a reference to the value in the Rc, and the result is returned, also in an Rc.

Note: this is an associated function, which means that you have to call it as Rc::map(r, f) instead of r.map(f). This is so that there is no conflict with a method on the inner type.

Examples

use std::rc::Rc;

let r = Rc::new(7);
let new = Rc::map(r, |i| i + 7);
assert_eq!(*new, 14);

Attempts to map the value in an Rc, reusing the allocation if possible.

f is called on a reference to the value in the Rc, and if the operation succeeds, the result is returned, also in an Rc.

Note: this is an associated function, which means that you have to call it as Rc::try_map(r, f) instead of r.try_map(f). This is so that there is no conflict with a method on the inner type.

Examples

#![feature(smart_pointer_try_map)]

use std::rc::Rc;

let b = Rc::new(7);
let new = Rc::try_map(b, |&i| u32::try_from(i)).unwrap();
assert_eq!(*new, 7);

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

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])

Constructs a new reference-counted slice with uninitialized contents.

Examples

#![feature(get_mut_unchecked)]
#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let mut values = Rc::<[u32], _>::new_uninit_slice_in(3, System);

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])

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(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let values = Rc::<[u32], _>::new_zeroed_slice_in(3, System);
let values = unsafe { values.assume_init() };

assert_eq!(*values, [0, 0, 0])

Converts the reference-counted slice into a reference-counted array.

This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.

Errors

Returns the original Rc<[T]> in the Err variant if self.len() does not equal N.

Examples

#![feature(alloc_slice_into_array)]
use std::rc::Rc;

let rc_slice: Rc<[i32]> = Rc::new([1, 2, 3]);

let rc_array: Rc<[i32; 3]> = rc_slice.into_array().unwrap();

Allocates an RcInner<[T]> with the given length.

Constructs a new Rc<T> with a clone of value.

Examples

#![feature(clone_from_ref)]
use std::rc::Rc;

let hello: Rc<str> = Rc::clone_from_ref("hello");

Constructs a new Rc<T> with a clone of value, returning an error if allocation fails

Examples

#![feature(clone_from_ref)]
use std::rc::Rc;

let hello: Rc<str> = Rc::try_clone_from_ref("hello")?;
# Ok::<(), std::alloc::AllocError>(())

Constructs a new Rc<T> with a clone of value in the provided allocator.

Examples

#![feature(clone_from_ref)]
#![feature(allocator_ext)]
use std::rc::Rc;
use std::alloc::System;

let hello: Rc<str, System> = Rc::clone_from_ref_in("hello", System);

Constructs a new Rc<T> with a clone of value in the provided allocator, returning an error if allocation fails

Examples

#![feature(clone_from_ref)]
#![feature(allocator_ext)]
use std::rc::Rc;
use std::alloc::System;

let hello: Rc<str, System> = Rc::try_clone_from_ref_in("hello", System)?;
# Ok::<(), std::alloc::AllocError>(())

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 disassociating 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());

Constructs an Rc<T> from a raw pointer.

The raw pointer must have been previously returned by a call to Rc<U>::into_raw or Rc<U>::into_raw_with_allocator.

Safety

• Creating a Rc<T> from a pointer other than one returned from Rc<U>::into_raw or Rc<U>::into_raw_with_allocator is undefined behavior.
• If U is sized, it must have the same size and alignment as T. This is trivially true if U is T.
• If U is unsized, its data pointer must have the same size and alignment as T. This is trivially true if Rc<U> was constructed through Rc<T> and then converted to Rc<U> through an unsized coercion.
• Note that if U or U's data pointer 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 raw pointer must point to a block of memory allocated by the global allocator
• 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!

Convert a slice back into its original array:

use std::rc::Rc;

let x: Rc<[u32]> = Rc::new([1, 2, 3]);
let x_ptr: *const [u32] = Rc::into_raw(x);

unsafe {
    let x: Rc<[u32; 3]> = Rc::from_raw(x_ptr.cast::<[u32; 3]>());
    assert_eq!(&*x, &[1, 2, 3]);
}

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");
# // Prevent leaks for Miri.
# drop(unsafe { Rc::from_raw(x_ptr) });

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 must satisfy the same layout requirements specified in Rc::from_raw_in. The associated Rc instance must be valid (i.e. the strong count must be at least 1) for the duration of this method, and ptr must point to a block of memory allocated by the global allocator.

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));
#   // Prevent leaks for Miri.
#   Rc::decrement_strong_count(ptr);
}

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 must satisfy the same layout requirements specified in Rc::from_raw_in. The associated Rc instance must be valid (i.e. the strong count must be at least 1) when invoking this method, and ptr must point to a block of memory allocated by the global allocator. 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));
}

Gets the number of strong (Rc) pointers to the allocation behind the given raw pointer.

This method does not consume or drop the Rc behind this pointer.

Safety

The pointer must point to (and have valid metadata for) the value inside a live Rc allocation, such as a pointer returned by Rc::into_raw, Rc::into_raw_with_allocator, or Rc::as_ptr. T must have the same alignment as that value. The associated Rc instance must be valid (i.e. the strong count must be at least 1) for the duration of this method.

Examples

#![feature(arc_raw_get_strong)]
use std::rc::Rc;

let five = Rc::new(5);
let _also_five = Rc::clone(&five);
let ptr = Rc::into_raw(five);

unsafe {
    assert_eq!(2, Rc::strong_count_from_raw(ptr));

    // Convert back to an `Rc` to avoid leaking memory.
    let five = Rc::from_raw(ptr);
    assert_eq!(2, Rc::strong_count(&five));
}

Allocates an RcInner<T> with sufficient space for a possibly-unsized inner value where the value has the layout provided.

The function mem_to_rc_inner is called with the data pointer and must return back a (potentially fat)-pointer for the RcInner<T>.

Allocates an RcInner<T> with sufficient space for a possibly-unsized inner value where the value has the layout provided, returning an error if allocation fails.

The function mem_to_rc_inner is called with the data pointer and must return back a (potentially fat)-pointer for the RcInner<T>.

Allocates an RcInner<T> with sufficient space for an unsized inner value

Returns a reference to the underlying allocator.

Note: this is an associated function, which means that you have to call it as Rc::allocator(&r) instead of r.allocator(). This is so that there is no conflict with a method on the inner type.

Consumes the Rc, returning the wrapped pointer and allocator.

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

Examples

#![feature(allocator_ext)]
use std::rc::Rc;
use std::alloc::System;

let x = Rc::new_in("hello".to_owned(), System);
let (ptr, alloc) = Rc::into_raw_with_allocator(x);
assert_eq!(unsafe { &*ptr }, "hello");
let x = unsafe { Rc::from_raw_in(ptr, alloc) };
assert_eq!(&*x, "hello");

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 as there are strong counts in the Rc.

Examples

use std::rc::Rc;

let x = Rc::new(0);
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 }, 0);

Constructs an Rc<T, A> from a raw pointer in the provided allocator.

The raw pointer must have been previously returned by a call to Rc<U, A>::into_raw or Rc<U, A>::into_raw_with_allocator.

Safety

• Creating a Rc<T, A> from a pointer other than one returned from Rc<U, A>::into_raw or Rc<U, A>::into_raw_with_allocator is undefined behavior.
• If U is sized, it must have the same size and alignment as T. This is trivially true if U is T.
• If U is unsized, its data pointer must have the same size and alignment as T. This is trivially true if Rc<U, A> was constructed through Rc<T, A> and then converted to Rc<U, A> through an unsized coercion.
• Note that if U or U's data pointer 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 raw pointer must point to a block of memory allocated by alloc
• 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, A> is never accessed.

Examples

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let x = Rc::new_in("hello".to_owned(), System);
let (x_ptr, _alloc) = Rc::into_raw_with_allocator(x);

unsafe {
    // Convert back to an `Rc` to prevent leak.
    let x = Rc::from_raw_in(x_ptr, System);
    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!

Convert a slice back into its original array:

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let x: Rc<[u32], _> = Rc::new_in([1, 2, 3], System);
let x_ptr: *const [u32] = Rc::into_raw_with_allocator(x).0;

unsafe {
    let x: Rc<[u32; 3], _> = Rc::from_raw_in(x_ptr.cast::<[u32; 3]>(), System);
    assert_eq!(&*x, &[1, 2, 3]);
}

Creates a new Weak pointer to this allocation.

Examples

use std::rc::Rc;

let five = Rc::new(5);

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

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));

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));

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 must satisfy the same layout requirements specified in Rc::from_raw_in. The associated Rc instance must be valid (i.e. the strong count must be at least 1) for the duration of this method, and ptr must point to a block of memory allocated by alloc.

Examples

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let five = Rc::new_in(5, System);

unsafe {
    let (ptr, _alloc) = Rc::into_raw_with_allocator(five);
    Rc::increment_strong_count_in(ptr, System);

    let five = Rc::from_raw_in(ptr, System);
    assert_eq!(2, Rc::strong_count(&five));
#   // Prevent leaks for Miri.
#   Rc::decrement_strong_count_in(ptr, System);
}

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_rawand must satisfy the same layout requirements specified in Rc::from_raw_in. The associated Rc instance must be valid (i.e. the strong count must be at least 1) when invoking this method, and ptr must point to a block of memory allocated by alloc. 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

#![feature(allocator_ext)]

use std::rc::Rc;
use std::alloc::System;

let five = Rc::new_in(5, System);

unsafe {
    let (ptr, _alloc) = Rc::into_raw_with_allocator(five);
    Rc::increment_strong_count_in(ptr, System);

    let five = Rc::from_raw_in(ptr, System);
    assert_eq!(2, Rc::strong_count(&five));
    Rc::decrement_strong_count_in(ptr, System);
    assert_eq!(1, Rc::strong_count(&five));
}

Determine whether this is the unique reference to the underlying data.

Returns true if there are no other Rc or Weak pointers to the same allocation; returns false otherwise.

If this function returns true, it is safe to call get_mut_unchecked immediately afterward.

Examples

#![feature(arc_is_unique)]

use std::rc::Rc;

let x = Rc::new(3);
assert!(Rc::is_unique(&x));

let y = Rc::clone(&x);
assert!(!Rc::is_unique(&x));
drop(y);

// Weak references also count, because they could be upgraded at any time.
let z = Rc::downgrade(&x);
assert!(!Rc::is_unique(&x));

Pointer invalidation

This function will always return the same value as Rc::get_mut(rc).is_some(). However, unlike that operation it does not produce any mutable references to the underlying data, meaning no pointers to the data inside the Rc are invalidated by the call. Thus, the following code is valid, even though it would be UB if it used Rc::get_mut:

#![feature(arc_is_unique)]

use std::rc::Rc;

let rc = Rc::new(5);
let pointer: *const i32 = &*rc;
assert!(Rc::is_unique(&rc));
assert_eq!(unsafe { *pointer }, 5);

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());

Returns a mutable reference into the given Rc, without any check.

See also get_mut, which is safe and does appropriate checks.

Safety

If any other Rc or Weak pointers to the same allocation exist, then they must not be dereferenced or have active borrows for the duration of the returned borrow, and their inner type must be exactly the same as the inner type of this Rc (including lifetimes). 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");

Other Rc pointers to the same allocation must be to the same type.

#![feature(get_mut_unchecked)]

use std::rc::Rc;

let x: Rc<str> = Rc::from("Hello, world!");
let mut y: Rc<[u8]> = x.clone().into();
unsafe {
    // this is Undefined Behavior, because x's inner type is str, not [u8]
    Rc::get_mut_unchecked(&mut y).fill(0xff); // 0xff is invalid in UTF-8
}
println!("{}", &*x); // Invalid UTF-8 in a str

Other Rc pointers to the same allocation must be to the exact same type, including lifetimes.

#![feature(get_mut_unchecked)]

use std::rc::Rc;

let x: Rc<&str> = Rc::new("Hello, world!");
{
    let s = String::from("Oh, no!");
    let mut y: Rc<&str> = x.clone();
    unsafe {
        // this is Undefined Behavior, because x's inner type
        // is &'long str, not &'short str
        *Rc::get_mut_unchecked(&mut y) = &s;
    }
}
println!("{}", &*x); // Use-after-free

Returns true if the two Rcs point to the same allocation in a vein similar to ptr::eq. This function ignores the metadata of dyn Trait pointers.

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));

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

# use std::{ptr, rc::Rc};
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()));