Struct alloc::sync::Arc

1.0.0 · source · [−]
pub struct Arc<T: ?Sized> { /* private fields */ }
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 upgraded 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(());
let my_weak = 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:?}");
    });
}
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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

Constructs a new Arc<T>.

Examples
use std::sync::Arc;

let five = Arc::new(5);
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Constructs a new Arc<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 Arc<T> is created, such that you can clone and store it inside the T.

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

Since the new Arc<T> is not fully-constructed until Arc<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.

Example
use std::sync::{Arc, Weak};

struct Gadget {
    me: Weak<Gadget>,
}

impl Gadget {
    /// Construct a reference counted Gadget.
    fn new() -> Arc<Self> {
        // `me` is a `Weak<Gadget>` pointing at the new allocation of the
        // `Arc` we're constructing.
        Arc::new_cyclic(|me| {
            // Create the actual struct here.
            Gadget { me: me.clone() }
        })
    }

    /// Return a reference counted pointer to Self.
    fn me(&self) -> Arc<Self> {
        self.me.upgrade().unwrap()
    }
}
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🔬 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();

// Deferred initialization:
Arc::get_mut(&mut five).unwrap().write(5);

let five = unsafe { five.assume_init() };

assert_eq!(*five, 5)
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🔬 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)
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Constructs a new Pin<Arc<T>>. If T does not implement Unpin, then data will be pinned in memory and unable to be moved.

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

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

🔬 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)?;
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🔬 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()?;

// Deferred initialization:
Arc::get_mut(&mut five).unwrap().write(5);

let five = unsafe { five.assume_init() };

assert_eq!(*five, 5);
Run
🔬 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);
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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);
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🔬 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);

// Deferred initialization:
let data = Arc::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])
Run
🔬 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
🔬 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();

// Deferred initialization:
Arc::get_mut(&mut five).unwrap().write(5);

let five = unsafe { five.assume_init() };

assert_eq!(*five, 5)
Run
🔬 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);

// Deferred initialization:
let data = Arc::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])
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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");
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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");
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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!
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Creates a new Weak pointer to this allocation.

Examples
use std::sync::Arc;

let five = Arc::new(5);

let weak_five = Arc::downgrade(&five);
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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));
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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));
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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));
}
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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));
}
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Returns true if the two Arcs 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));
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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 dissociated and the inner value will not be cloned.

See also get_mut, which will fail rather than cloning the inner value or dissociating 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);
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Weak pointers will be dissociated:

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());
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🔬 This is a nightly-only experimental API. (arc_unwrap_or_clone #93610)

If we have the only reference to T then unwrap it. Otherwise, clone T and return the clone.

Assuming arc_t is of type Arc<T>, this function is functionally equivalent to (*arc_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 arc = Arc::new(inner);
let inner = Arc::unwrap_or_clone(arc);
// The inner value was not cloned
assert!(ptr::eq(ptr, inner.as_ptr()));

let arc = Arc::new(inner);
let arc2 = arc.clone();
let inner = Arc::unwrap_or_clone(arc);
// Because there were 2 references, we had to clone the inner value.
assert!(!ptr::eq(ptr, inner.as_ptr()));
// `arc2` is the last reference, so when we unwrap it we get back
// the original `String`.
let inner = Arc::unwrap_or_clone(arc2);
assert!(ptr::eq(ptr, inner.as_ptr()));
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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());
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🔬 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");
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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));
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🔬 This is a nightly-only experimental API. (downcast_unchecked #90850)

Downcasts the Arc<dyn Any + Send + Sync> to a concrete type.

For a safe alternative see downcast.

Examples
#![feature(downcast_unchecked)]

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

let x: Arc<dyn Any + Send + Sync> = Arc::new(1_usize);

unsafe {
    assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}
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Safety

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

Trait Implementations

Converts this type into a shared reference of the (usually inferred) input type.

Immutably borrows from an owned value. Read more

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);
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Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

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);
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The resulting type after dereferencing.

Dereferences the value.

Formats the value using the given formatter. Read more

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!"
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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[..]);
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Converts a &CStr into a Arc<CStr>, by copying the contents into a newly allocated Arc.

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

Example
let shared: Arc<str> = Arc::from("eggplant");
assert_eq!("eggplant", &shared[..]);
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Use a Wake-able type as a Waker.

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

Use a Wake-able type as a RawWaker.

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

Converts an atomically reference-counted string slice into a byte slice.

Example
let string: Arc<str> = Arc::from("eggplant");
let bytes: Arc<[u8]> = Arc::from(string);
assert_eq!("eggplant".as_bytes(), bytes.as_ref());
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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[..]);
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Converts a CString into an Arc<CStr> by moving the CString data into a new Arc buffer.

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[..]);
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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[..]);
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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);
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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[..]);
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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();
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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.
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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.
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Feeds this value into the given Hasher. Read more

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

Comparison for two Arcs.

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)));
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Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

Equality for two Arcs.

Two Arcs 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 Arcs that point to the same allocation are always equal.

Examples
use std::sync::Arc;

let five = Arc::new(5);

assert!(five == Arc::new(5));
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Inequality for two Arcs.

Two Arcs are unequal if their inner values are unequal.

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

Examples
use std::sync::Arc;

let five = Arc::new(5);

assert!(five != Arc::new(6));
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Partial comparison for two Arcs.

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)));
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Less-than comparison for two Arcs.

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));
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‘Less than or equal to’ comparison for two Arcs.

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));
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Greater-than comparison for two Arcs.

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

‘Greater than or equal to’ comparison for two Arcs.

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

Formats the value using the given formatter.

The type returned in the event of a conversion error.

Performs the conversion.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Converts to this type from the input type.

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.

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

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

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.