Arc in alloc::sync - Rust
Description: A thread-safe reference-counting pointer. ‘Arc’ stands for ‘Atomically Reference Counted’.
Keywords: rust, rustlang, rust-lang, Arc

# Struct alloc::sync::Arc
1.0.0[−][src]

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

Expand description

A thread-safe reference-counting pointer. ‘Arc’ stands for ‘Atomically Reference Counted’.

The type `Arc<T>` provides shared ownership of a value of type `T`, allocated in the heap. Invoking `clone` on `Arc` produces a new `Arc` instance, which points to the same allocation on the heap as the source `Arc`, while increasing a reference count. When the last `Arc` pointer to a given allocation is destroyed, the value stored in that allocation (often referred to as “inner value”) is also dropped.

Shared references in Rust disallow mutation by default, and `Arc` is no exception: you cannot generally obtain a mutable reference to something inside an `Arc`. If you need to mutate through an `Arc`, use `Mutex`, `RwLock`, or one of the `Atomic` types.

## Thread Safety

Unlike `Rc<T>`, `Arc<T>` uses atomic operations for its reference counting. This means that it is thread-safe. The disadvantage is that atomic operations are more expensive than ordinary memory accesses. If you are not sharing reference-counted allocations between threads, consider using `Rc<T>` for lower overhead. `Rc<T>` is a safe default, because the compiler will catch any attempt to send an `Rc<T>` between threads. However, a library might choose `Arc<T>` in order to give library consumers more flexibility.

`Arc<T>` will implement `Send` and `Sync` as long as the `T` implements `Send` and `Sync`. Why can’t you put a non-thread-safe type `T` in an `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at first: after all, isn’t the point of `Arc<T>` thread safety? The key is this: `Arc<T>` makes it thread safe to have multiple ownership of the same data, but it doesn’t add thread safety to its data. Consider `Arc<``RefCell<T>``>`. `RefCell<T>` isn’t `Sync`, and if `Arc<T>` was always `Send`, `Arc<``RefCell<T>``>` would be as well. But then we’d have a problem: `RefCell<T>` is not thread safe; it keeps track of the borrowing count using non-atomic operations.

In the end, this means that you may need to pair `Arc<T>` with some sort of `std::sync` type, usually `Mutex<T>`.

## Breaking cycles with `Weak`

The `downgrade` method can be used to create a non-owning `Weak` pointer. A `Weak` pointer can be `upgrade`d to an `Arc`, but this will return `None` if the value stored in the allocation has already been dropped. In other words, `Weak` pointers do not keep the value inside the allocation alive; however, they do keep the allocation (the backing store for the value) alive.

A cycle between `Arc` pointers will never be deallocated. For this reason, `Weak` is used to break cycles. For example, a tree could have strong `Arc` pointers from parent nodes to children, and `Weak` pointers from children back to their parents.

# Cloning references

Creating a new reference from an existing reference-counted pointer is done using the `Clone` trait implemented for `Arc<T>` and `Weak<T>`.

    use std::sync::Arc;
    let foo = Arc::new(vec![1.0, 2.0, 3.0]);
    // The two syntaxes below are equivalent.
    let a = foo.clone();
    let b = Arc::clone(&foo);
    // a, b, and foo are all Arcs that point to the same memory location

Run

## `Deref` behavior

`Arc<T>` automatically dereferences to `T` (via the `Deref` trait), so you can call `T`’s methods on a value of type `Arc<T>`. To avoid name clashes with `T`’s methods, the methods of `Arc<T>` itself are associated functions, called using fully qualified syntax:

    use std::sync::Arc;

    let my_arc = Arc::new(());
    Arc::downgrade(&my_arc);

Run

`Arc<T>`’s implementations of traits like `Clone` may also be called using fully qualified syntax. Some people prefer to use fully qualified syntax, while others prefer using method-call syntax.

    use std::sync::Arc;

    let arc = Arc::new(());
    // Method-call syntax
    let arc2 = arc.clone();
    // Fully qualified syntax
    let arc3 = Arc::clone(&arc);

Run

`Weak<T>` does not auto-dereference to `T`, because the inner value may have already been dropped.

# Examples

Sharing some immutable data between threads:

    use std::sync::Arc;
    use std::thread;

    let five = Arc::new(5);

    for _ in 0..10 {
        let five = Arc::clone(&five);

        thread::spawn(move || {
            println!("{:?}", five);
        });
    }

Run

Sharing a mutable `AtomicUsize`:

    use std::sync::Arc;
    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::thread;

    let val = Arc::new(AtomicUsize::new(5));

    for _ in 0..10 {
        let val = Arc::clone(&val);

        thread::spawn(move || {
            let v = val.fetch_add(1, Ordering::SeqCst);
            println!("{:?}", v);
        });
    }

Run

See the `rc` documentation for more examples of reference counting in general.

## Implementations

[src]

### impl<T> Arc<T>

[src]

#### pub fn new(data: T) -> Arc<T>

Constructs a new `Arc<T>`.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

Run
[src]

#### pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Arc<T>

🔬 This is a nightly-only experimental API. (`arc_new_cyclic` #75861)

Constructs a new `Arc<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::sync::{Arc, Weak};

    struct Foo {
        me: Weak<Foo>,
    }

    let foo = Arc::new_cyclic(|me| Foo {
        me: me.clone(),
    });

Run
[src]

#### pub fn new_uninit() -> Arc<MaybeUninit<T>>

🔬 This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new `Arc` with uninitialized contents.

# Examples

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

    use std::sync::Arc;

    let mut five = Arc::<u32>::new_uninit();

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

        five.assume_init()
    };

    assert_eq!(*five, 5)

Run
[src]

#### pub fn new_zeroed() -> Arc<MaybeUninit<T>>

🔬 This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new `Arc` 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::sync::Arc;

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

    assert_eq!(*zero, 0)

Run
1.33.0[src]

#### pub fn pin(data: T) -> Pin<Arc<T>>

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

[src]

#### pub fn try_pin(data: T) -> Result<Pin<Arc<T>>, AllocError>

🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new `Pin<Arc<T>>`, return an error if allocation fails.

[src]

#### pub fn try_new(data: T) -> Result<Arc<T>, AllocError>

🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new `Arc<T>`, returning an error if allocation fails.

# Examples

    #![feature(allocator_api)]
    use std::sync::Arc;

    let five = Arc::try_new(5)?;

Run
[src]

#### pub fn try_new_uninit() -> Result<Arc<MaybeUninit<T>>, AllocError>

🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new `Arc` with uninitialized contents, returning an error if allocation fails.

# Examples

    #![feature(new_uninit, allocator_api)]
    #![feature(get_mut_unchecked)]

    use std::sync::Arc;

    let mut five = Arc::<u32>::try_new_uninit()?;

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

        five.assume_init()
    };

    assert_eq!(*five, 5);

Run
[src]

#### pub fn try_new_zeroed() -> Result<Arc<MaybeUninit<T>>, AllocError>

🔬 This is a nightly-only experimental API. (`allocator_api` #32838)

Constructs a new `Arc` with uninitialized contents, with the memory being filled with `0` bytes, returning an error if allocation fails.

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

# Examples

    #![feature(new_uninit, allocator_api)]

    use std::sync::Arc;

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

    assert_eq!(*zero, 0);

Run
1.4.0[src]

#### pub fn try_unwrap(this: Self) -> Result<T, Self>

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

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

This will succeed even if there are outstanding weak references.

# Examples

    use std::sync::Arc;

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

    let x = Arc::new(4);
    let _y = Arc::clone(&x);
    assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4);

Run
[src]

### impl<T> Arc<[T]>

[src]

#### pub fn new_uninit_slice(len: usize) -> Arc<[MaybeUninit<T>]>

🔬 This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new atomically reference-counted slice with uninitialized contents.

# Examples

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

    use std::sync::Arc;

    let mut values = Arc::<[u32]>::new_uninit_slice(3);

    let values = unsafe {
        // Deferred initialization:
        Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1);
        Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2);
        Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3);

        values.assume_init()
    };

    assert_eq!(*values, [1, 2, 3])

Run
[src]

#### pub fn new_zeroed_slice(len: usize) -> Arc<[MaybeUninit<T>]>

🔬 This is a nightly-only experimental API. (`new_uninit` #63291)

Constructs a new atomically 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::sync::Arc;

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

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

Run
[src]

### impl<T> Arc<MaybeUninit<T>>

[src]

#### pub unsafe fn assume_init(self) -> Arc<T>

🔬 This is a nightly-only experimental API. (`new_uninit` #63291)

Converts to `Arc<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::sync::Arc;

    let mut five = Arc::<u32>::new_uninit();

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

        five.assume_init()
    };

    assert_eq!(*five, 5)

Run
[src]

### impl<T> Arc<[MaybeUninit<T>]>

[src]

#### pub unsafe fn assume_init(self) -> Arc<[T]>

🔬 This is a nightly-only experimental API. (`new_uninit` #63291)

Converts to `Arc<[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::sync::Arc;

    let mut values = Arc::<[u32]>::new_uninit_slice(3);

    let values = unsafe {
        // Deferred initialization:
        Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1);
        Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2);
        Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3);

        values.assume_init()
    };

    assert_eq!(*values, [1, 2, 3])

Run
[src]

### impl<T: ?Sized> Arc<T>

1.17.0[src]

#### pub fn into_raw(this: Self) -> *const T

Consumes the `Arc`, returning the wrapped pointer.

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

# Examples

    use std::sync::Arc;

    let x = Arc::new("hello".to_owned());
    let x_ptr = Arc::into_raw(x);
    assert_eq!(unsafe { &*x_ptr }, "hello");

Run
1.45.0[src]

#### pub fn as_ptr(this: &Self) -> *const T

Provides a raw pointer to the data.

The counts are not affected in any way and the `Arc` is not consumed. The pointer is valid for as long as there are strong counts in the `Arc`.

# Examples

    use std::sync::Arc;

    let x = Arc::new("hello".to_owned());
    let y = Arc::clone(&x);
    let x_ptr = Arc::as_ptr(&x);
    assert_eq!(x_ptr, Arc::as_ptr(&y));
    assert_eq!(unsafe { &*x_ptr }, "hello");

Run
1.17.0[src]

#### pub unsafe fn from_raw(ptr: *const T) -> Self

Constructs an `Arc<T>` from a raw pointer.

The raw pointer must have been previously returned by a call to `Arc<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 `Arc<T>` is never accessed.

# Examples

    use std::sync::Arc;

    let x = Arc::new("hello".to_owned());
    let x_ptr = Arc::into_raw(x);

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

        // Further calls to `Arc::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!

Run
1.4.0[src]

#### pub fn downgrade(this: &Self) -> Weak<T>

Creates a new `Weak` pointer to this allocation.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
1.15.0[src]

#### pub fn weak_count(this: &Self) -> usize

Gets the number of `Weak` pointers to this allocation.

# Safety

This method by itself is safe, but using it correctly requires extra care. Another thread can change the weak count at any time, including potentially between calling this method and acting on the result.

# Examples

    use std::sync::Arc;

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

    // This assertion is deterministic because we haven't shared
    // the `Arc` or `Weak` between threads.
    assert_eq!(1, Arc::weak_count(&five));

Run
1.15.0[src]

#### pub fn strong_count(this: &Self) -> usize

Gets the number of strong (`Arc`) pointers to this allocation.

# Safety

This method by itself is safe, but using it correctly requires extra care. Another thread can change the strong count at any time, including potentially between calling this method and acting on the result.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);
    let _also_five = Arc::clone(&five);

    // This assertion is deterministic because we haven't shared
    // the `Arc` between threads.
    assert_eq!(2, Arc::strong_count(&five));

Run
1.51.0[src]

#### pub unsafe fn increment_strong_count(ptr: *const T)

Increments the strong reference count on the `Arc<T>` associated with the provided pointer by one.

# Safety

The pointer must have been obtained through `Arc::into_raw`, and the associated `Arc` instance must be valid (i.e. the strong count must be at least 1) for the duration of this method.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

    unsafe {
        let ptr = Arc::into_raw(five);
        Arc::increment_strong_count(ptr);

        // This assertion is deterministic because we haven't shared
        // the `Arc` between threads.
        let five = Arc::from_raw(ptr);
        assert_eq!(2, Arc::strong_count(&five));
    }

Run
1.51.0[src]

#### pub unsafe fn decrement_strong_count(ptr: *const T)

Decrements the strong reference count on the `Arc<T>` associated with the provided pointer by one.

# Safety

The pointer must have been obtained through `Arc::into_raw`, and the associated `Arc` 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 `Arc` and backing storage, but should not be called after the final `Arc` has been released.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

    unsafe {
        let ptr = Arc::into_raw(five);
        Arc::increment_strong_count(ptr);

        // Those assertions are deterministic because we haven't shared
        // the `Arc` between threads.
        let five = Arc::from_raw(ptr);
        assert_eq!(2, Arc::strong_count(&five));
        Arc::decrement_strong_count(ptr);
        assert_eq!(1, Arc::strong_count(&five));
    }

Run
1.17.0[src]

#### pub fn ptr_eq(this: &Self, other: &Self) -> bool

Returns `true` if the two `Arc`s point to the same allocation (in a vein similar to `ptr::eq`).

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);
    let same_five = Arc::clone(&five);
    let other_five = Arc::new(5);

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

Run
[src]

### impl<T: Clone> Arc<T>

1.4.0[src]

#### pub fn make_mut(this: &mut Self) -> &mut T

Makes a mutable reference into the given `Arc`.

If there are other `Arc` 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 `Arc` 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::sync::Arc;

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

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

Run

`Weak` pointers will be disassociated:

    use std::sync::Arc;

    let mut data = Arc::new(75);
    let weak = Arc::downgrade(&data);

    assert!(75 == *data);
    assert!(75 == *weak.upgrade().unwrap());

    *Arc::make_mut(&mut data) += 1;

    assert!(76 == *data);
    assert!(weak.upgrade().is_none());

Run
[src]

### impl<T: ?Sized> Arc<T>

1.4.0[src]

#### pub fn get_mut(this: &mut Self) -> Option<&mut T>

Returns a mutable reference into the given `Arc`, if there are no other `Arc` 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 `Arc` pointers.

# Examples

    use std::sync::Arc;

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

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

Run
[src]

#### pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T

🔬 This is a nightly-only experimental API. (`get_mut_unchecked` #63292)

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

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

# Safety

Any other `Arc` 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 `Arc::new`.

# Examples

    #![feature(get_mut_unchecked)]

    use std::sync::Arc;

    let mut x = Arc::new(String::new());
    unsafe {
        Arc::get_mut_unchecked(&mut x).push_str("foo")
    }
    assert_eq!(*x, "foo");

Run
[src]

### impl Arc<dyn Any + Send + Sync>

1.29.0[src]

#### pub fn downcast<T>(self) -> Result<Arc<T>, Self> where
T: Any + Send + Sync + 'static,

Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type.

# Examples

    use std::any::Any;
    use std::sync::Arc;

    fn print_if_string(value: Arc<dyn Any + Send + Sync>) {
        if let Ok(string) = value.downcast::<String>() {
            println!("String ({}): {}", string.len(), string);
        }
    }

    let my_string = "Hello World".to_string();
    print_if_string(Arc::new(my_string));
    print_if_string(Arc::new(0i8));

Run

## Trait Implementations

1.5.0[src]

### impl<T: ?Sized> AsRef<T> for Arc<T>

[src]

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

Performs the conversion.

[src]

### impl<T: ?Sized> Borrow<T> for Arc<T>

[src]

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

Immutably borrows from an owned value. Read more

[src]

### impl<T: ?Sized> Clone for Arc<T>

[src]

#### fn clone(&self) -> Arc<T>

Makes a clone of the `Arc` pointer.

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

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

    let _ = Arc::clone(&five);

Run
[src]

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

Performs copy-assignment from `source`. Read more

[src]

### impl<T: ?Sized + Debug> Debug for Arc<T>

[src]

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

Formats the value using the given formatter. Read more

[src]

### impl<T: Default> Default for Arc<T>

[src]

#### fn default() -> Arc<T>

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

# Examples

    use std::sync::Arc;

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

Run
[src]

### impl<T: ?Sized> Deref for Arc<T>

#### type Target = T

The resulting type after dereferencing.

[src]

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

Dereferences the value.

[src]

### impl<T: ?Sized + Display> Display for Arc<T>

[src]

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

Formats the value using the given formatter. Read more

[src]

### impl<T: ?Sized> Drop for Arc<T>

[src]

#### fn drop(&mut self)

Drops the `Arc`.

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::sync::Arc;

    struct Foo;

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

    let foo  = Arc::new(Foo);
    let foo2 = Arc::clone(&foo);

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

Run
1.21.0[src]

### impl<T: Clone> From<&'_ [T]> for Arc<[T]>

[src]

#### fn from(v: &[T]) -> Arc<[T]>

Allocate a reference-counted slice and fill it by cloning `v`’s items.

# Example

    let original: &[i32] = &[1, 2, 3];
    let shared: Arc<[i32]> = Arc::from(original);
    assert_eq!(&[1, 2, 3], &shared[..]);

Run
1.21.0[src]

### impl From<&'_ str> for Arc<str>

[src]

#### fn from(v: &str) -> Arc<str>

Allocate a reference-counted `str` and copy `v` into it.

# Example

    let shared: Arc<str> = Arc::from("eggplant");
    assert_eq!("eggplant", &shared[..]);

Run
1.51.0[src]

### impl<W: Wake + Send + Sync + 'static> From<Arc<W>> for Waker

[src]

#### fn from(waker: Arc<W>) -> Waker

Use a `Wake`-able type as a `Waker`.

No heap allocations or atomic operations are used for this conversion.

1.51.0[src]

### impl<W: Wake + Send + Sync + 'static> From<Arc<W>> for RawWaker

[src]

#### fn from(waker: Arc<W>) -> RawWaker

Use a `Wake`-able type as a `RawWaker`.

No heap allocations or atomic operations are used for this conversion.

1.21.0[src]

### impl<T: ?Sized> From<Box<T, Global>> for Arc<T>

[src]

#### fn from(v: Box<T>) -> Arc<T>

Move a boxed object to a new, reference-counted allocation.

# Example

    let unique: Box<str> = Box::from("eggplant");
    let shared: Arc<str> = Arc::from(unique);
    assert_eq!("eggplant", &shared[..]);

Run
1.45.0[src]

### impl<'a, B: ?Sized> From<Cow<'a, B>> for Arc<B> where
B: ToOwned + ?Sized,
Arc<B>: From<&'a B> + From<B::Owned>,

[src]

#### fn from(cow: Cow<'a, B>) -> Arc<B>

Create an atomically reference-counted pointer from a clone-on-write pointer by copying its content.

# Example

    let cow: Cow<str> = Cow::Borrowed("eggplant");
    let shared: Arc<str> = Arc::from(cow);
    assert_eq!("eggplant", &shared[..]);

Run
1.21.0[src]

### impl From<String> for Arc<str>

[src]

#### fn from(v: String) -> Arc<str>

Allocate a reference-counted `str` and copy `v` into it.

# Example

    let unique: String = "eggplant".to_owned();
    let shared: Arc<str> = Arc::from(unique);
    assert_eq!("eggplant", &shared[..]);

Run
1.6.0[src]

### impl<T> From<T> for Arc<T>

[src]

#### fn from(t: T) -> Self

Converts a `T` into an `Arc<T>`

The conversion moves the value into a newly allocated `Arc`. It is equivalent to calling `Arc::new(t)`.

# Example

    let x = 5;
    let arc = Arc::new(5);

    assert_eq!(Arc::from(x), arc);

Run
1.21.0[src]

### impl<T> From<Vec<T, Global>> for Arc<[T]>

[src]

#### fn from(v: Vec<T>) -> Arc<[T]>

Allocate a reference-counted slice and move `v`’s items into it.

# Example

    let unique: Vec<i32> = vec![1, 2, 3];
    let shared: Arc<[i32]> = Arc::from(unique);
    assert_eq!(&[1, 2, 3], &shared[..]);

Run
1.37.0[src]

### impl<T> FromIterator<T> for Arc<[T]>

[src]

#### fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self

Takes each element in the `Iterator` and collects it into an `Arc<[T]>`.

# Performance characteristics

## The general case

In the general case, collecting into `Arc<[T]>` is done by first collecting into a `Vec<T>`. That is, when writing the following:

    let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();

Run

this behaves as if we wrote:

    let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0)
        .collect::<Vec<_>>() // The first set of allocations happens here.
        .into(); // A second allocation for `Arc<[T]>` happens here.

Run

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 `Arc<[T]>`.

## Iterators of known length

When your `Iterator` implements `TrustedLen` and is of an exact size, a single allocation will be made for the `Arc<[T]>`. For example:

    let evens: Arc<[u8]> = (0..10).collect(); // Just a single allocation happens here.

Run
[src]

### impl<T: ?Sized + Hash> Hash for Arc<T>

[src]

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

Feeds this value into the given `Hasher`. Read more

1.3.0[src]

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

Feeds a slice of this type into the given `Hasher`. Read more

[src]

### impl<T: ?Sized + Ord> Ord for Arc<T>

[src]

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

Comparison for two `Arc`s.

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

# Examples

    use std::sync::Arc;
    use std::cmp::Ordering;

    let five = Arc::new(5);

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

Run
1.21.0[src]

#### fn max(self, other: Self) -> Self

Compares and returns the maximum of two values. Read more

1.21.0[src]

#### fn min(self, other: Self) -> Self

Compares and returns the minimum of two values. Read more

1.50.0[src]

#### fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval. Read more

[src]

### impl<T: ?Sized + PartialEq> PartialEq<Arc<T>> for Arc<T>

[src]

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

Equality for two `Arc`s.

Two `Arc`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 `Arc`s that point to the same allocation are always equal.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
[src]

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

Inequality for two `Arc`s.

Two `Arc`s are unequal if their inner values are unequal.

If `T` also implements `Eq` (implying reflexivity of equality), two `Arc`s that point to the same value are never unequal.

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
[src]

### impl<T: ?Sized + PartialOrd> PartialOrd<Arc<T>> for Arc<T>

[src]

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

Partial comparison for two `Arc`s.

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

# Examples

    use std::sync::Arc;
    use std::cmp::Ordering;

    let five = Arc::new(5);

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

Run
[src]

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

Less-than comparison for two `Arc`s.

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

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
[src]

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

‘Less than or equal to’ comparison for two `Arc`s.

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

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
[src]

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

Greater-than comparison for two `Arc`s.

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

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
[src]

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

‘Greater than or equal to’ comparison for two `Arc`s.

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

# Examples

    use std::sync::Arc;

    let five = Arc::new(5);

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

Run
[src]

### impl<T: ?Sized> Pointer for Arc<T>

[src]

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

Formats the value using the given formatter.

1.43.0[src]

### impl<T, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]>

#### type Error = Arc<[T]>

The type returned in the event of a conversion error.

[src]

#### fn try_from(boxed_slice: Arc<[T]>) -> Result<Self, Self::Error>

Performs the conversion.

[src]

### impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T>

[src]

### impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Arc<U>> for Arc<T>

[src]

### impl<T: ?Sized + Eq> Eq for Arc<T>

[src]

### impl<T: ?Sized + Sync + Send> Send for Arc<T>

[src]

### impl<T: ?Sized + Sync + Send> Sync for Arc<T>

1.33.0[src]

### impl<T: ?Sized> Unpin for Arc<T>

1.9.0[src]

### impl<T: RefUnwindSafe + ?Sized> UnwindSafe for Arc<T>

## Auto Trait Implementations

### impl<T: ?Sized> RefUnwindSafe for Arc<T> where
T: RefUnwindSafe,

## Blanket Implementations

[src]

### impl<T> Any for T where
T: 'static + ?Sized,

[src]

#### pub fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more

[src]

### impl<T> Borrow<T> for T where
T: ?Sized,

[src]

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

Immutably borrows from an owned value. Read more

[src]

### impl<T> BorrowMut<T> for T where
T: ?Sized,

[src]

#### pub fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

[src]

### impl<T> From<!> for T

[src]

#### pub fn from(t: !) -> T

Performs the conversion.

[src]

### impl<T> From<T> for T

[src]

#### pub fn from(t: T) -> T

Performs the conversion.

[src]

### impl<T, U> Into<U> for T where
U: From<T>,

[src]

#### pub fn into(self) -> U

Performs the conversion.

[src]

### impl<T> ToOwned for T where
T: Clone,

#### type Owned = T

The resulting type after obtaining ownership.

[src]

#### pub fn to_owned(&Self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

[src]

#### pub fn clone_into(&Self, &mut T)

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

[src]

### impl<T> ToString for T where
T: Display + ?Sized,

[src]

#### pub default fn to_string(&Self) -> String

Converts the given value to a `String`. Read more

[src]

### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

[src]

#### pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

[src]

### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

[src]

#### pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.