# Struct std::sync::atomic::AtomicI8

1.34.0 · source ·

    #[repr(C, align(1))]pub struct AtomicI8 { /* private fields */ }

Expand description

An integer type which can be safely shared between threads.

This type has the same in-memory representation as the underlying integer type, `i8`.

For more about the differences between atomic types and non-atomic types as well as information about the portability of this type, please see the module-level documentation.

Note: This type is only available on platforms that support atomic loads and stores of `i8`.

## Implementations§

source§

### impl AtomicI8

const: 1.34.0 · source

#### pub const fn new(v: i8) -> AtomicI8

Creates a new atomic integer.

##### §Examples

    use std::sync::atomic::AtomicI8;

    let atomic_forty_two = AtomicI8::new(42);

Run
1.75.0 (const: unstable) · source

#### pub unsafe fn from_ptr<'a>(ptr: *mut i8) -> &'a AtomicI8

Creates a new reference to an atomic integer from a pointer.

##### §Examples

    #![feature(pointer_is_aligned)]
    use std::sync::atomic::{self, AtomicI8};
    use std::mem::align_of;

    // Get a pointer to an allocated value
    let ptr: *mut i8 = Box::into_raw(Box::new(0));

    assert!(ptr.is_aligned_to(align_of::<AtomicI8>()));

    {
        // Create an atomic view of the allocated value
        let atomic = unsafe {AtomicI8::from_ptr(ptr) };

        // Use `atomic` for atomic operations, possibly share it with other threads
        atomic.store(1, atomic::Ordering::Relaxed);
    }

    // It's ok to non-atomically access the value behind `ptr`,
    // since the reference to the atomic ended its lifetime in the block above
    assert_eq!(unsafe { *ptr }, 1);

    // Deallocate the value
    unsafe { drop(Box::from_raw(ptr)) }

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##### §Safety

- `ptr` must be aligned to `align_of::<AtomicI8>()` (note that on some platforms this can be bigger than `align_of::<i8>()`).
- `ptr` must be valid for both reads and writes for the whole lifetime `'a`.
- You must adhere to the Memory model for atomic accesses. In particular, it is not allowed to mix atomic and non-atomic accesses, or atomic accesses of different sizes, without synchronization.

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#### pub fn get_mut(&mut self) -> &mut i8

Returns a mutable reference to the underlying integer.

This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let mut some_var = AtomicI8::new(10);
    assert_eq!(*some_var.get_mut(), 10);
    *some_var.get_mut() = 5;
    assert_eq!(some_var.load(Ordering::SeqCst), 5);

Run
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#### pub fn from_mut(v: &mut i8) -> &mut AtomicI8

🔬This is a nightly-only experimental API. (`atomic_from_mut` #76314)

Get atomic access to a `&mut i8`.

##### §Examples

    #![feature(atomic_from_mut)]
    use std::sync::atomic::{AtomicI8, Ordering};

    let mut some_int = 123;
    let a = AtomicI8::from_mut(&mut some_int);
    a.store(100, Ordering::Relaxed);
    assert_eq!(some_int, 100);

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#### pub fn get_mut_slice(this: &mut [AtomicI8]) -> &mut [i8]

🔬This is a nightly-only experimental API. (`atomic_from_mut` #76314)

Get non-atomic access to a `&mut [AtomicI8]` slice

This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.

##### §Examples

    #![feature(atomic_from_mut, inline_const)]
    use std::sync::atomic::{AtomicI8, Ordering};

    let mut some_ints = [const { AtomicI8::new(0) }; 10];

    let view: &mut [i8] = AtomicI8::get_mut_slice(&mut some_ints);
    assert_eq!(view, [0; 10]);
    view
        .iter_mut()
        .enumerate()
        .for_each(|(idx, int)| *int = idx as _);

    std::thread::scope(|s| {
        some_ints
            .iter()
            .enumerate()
            .for_each(|(idx, int)| {
                s.spawn(move || assert_eq!(int.load(Ordering::Relaxed), idx as _));
            })
    });

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#### pub fn from_mut_slice(v: &mut [i8]) -> &mut [AtomicI8]

🔬This is a nightly-only experimental API. (`atomic_from_mut` #76314)

Get atomic access to a `&mut [i8]` slice.

##### §Examples

    #![feature(atomic_from_mut)]
    use std::sync::atomic::{AtomicI8, Ordering};

    let mut some_ints = [0; 10];
    let a = &*AtomicI8::from_mut_slice(&mut some_ints);
    std::thread::scope(|s| {
        for i in 0..a.len() {
            s.spawn(move || a[i].store(i as _, Ordering::Relaxed));
        }
    });
    for (i, n) in some_ints.into_iter().enumerate() {
        assert_eq!(i, n as usize);
    }

Run
const: unstable · source

#### pub fn into_inner(self) -> i8

Consumes the atomic and returns the contained value.

This is safe because passing `self` by value guarantees that no other threads are concurrently accessing the atomic data.

##### §Examples

    use std::sync::atomic::AtomicI8;

    let some_var = AtomicI8::new(5);
    assert_eq!(some_var.into_inner(), 5);

Run
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#### pub fn load(&self, order: Ordering) -> i8

Loads a value from the atomic integer.

`load` takes an `Ordering` argument which describes the memory ordering of this operation. Possible values are `SeqCst`, `Acquire` and `Relaxed`.

##### §Panics

Panics if `order` is `Release` or `AcqRel`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let some_var = AtomicI8::new(5);

    assert_eq!(some_var.load(Ordering::Relaxed), 5);

Run
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#### pub fn store(&self, val: i8, order: Ordering)

Stores a value into the atomic integer.

`store` takes an `Ordering` argument which describes the memory ordering of this operation. Possible values are `SeqCst`, `Release` and `Relaxed`.

##### §Panics

Panics if `order` is `Acquire` or `AcqRel`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let some_var = AtomicI8::new(5);

    some_var.store(10, Ordering::Relaxed);
    assert_eq!(some_var.load(Ordering::Relaxed), 10);

Run
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#### pub fn swap(&self, val: i8, order: Ordering) -> i8

Stores a value into the atomic integer, returning the previous value.

`swap` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let some_var = AtomicI8::new(5);

    assert_eq!(some_var.swap(10, Ordering::Relaxed), 5);

Run
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#### pub fn compare_and_swap(&self, current: i8, new: i8, order: Ordering) -> i8

👎Deprecated since 1.50.0: Use `compare_exchange` or `compare_exchange_weak` instead

Stores a value into the atomic integer if the current value is the same as the `current` value.

The return value is always the previous value. If it is equal to `current`, then the value was updated.

`compare_and_swap` also takes an `Ordering` argument which describes the memory ordering of this operation. Notice that even when using `AcqRel`, the operation might fail and hence just perform an `Acquire` load, but not have `Release` semantics. Using `Acquire` makes the store part of this operation `Relaxed` if it happens, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Migrating to `compare_exchange` and `compare_exchange_weak`

`compare_and_swap` is equivalent to `compare_exchange` with the following mapping for memory orderings:

Original | Success | Failure
--- | --- | ---
Relaxed | Relaxed | Relaxed
Acquire | Acquire | Acquire
Release | Release | Relaxed
AcqRel | AcqRel | Acquire
SeqCst | SeqCst | SeqCst

`compare_exchange_weak` is allowed to fail spuriously even when the comparison succeeds, which allows the compiler to generate better assembly code when the compare and swap is used in a loop.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let some_var = AtomicI8::new(5);

    assert_eq!(some_var.compare_and_swap(5, 10, Ordering::Relaxed), 5);
    assert_eq!(some_var.load(Ordering::Relaxed), 10);

    assert_eq!(some_var.compare_and_swap(6, 12, Ordering::Relaxed), 10);
    assert_eq!(some_var.load(Ordering::Relaxed), 10);

Run
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#### pub fn compare_exchange( &self, current: i8, new: i8, success: Ordering, failure: Ordering ) -> Result<i8, i8>

Stores a value into the atomic integer if the current value is the same as the `current` value.

The return value is a result indicating whether the new value was written and containing the previous value. On success this value is guaranteed to be equal to `current`.

`compare_exchange` takes two `Ordering` arguments to describe the memory ordering of this operation. `success` describes the required ordering for the read-modify-write operation that takes place if the comparison with `current` succeeds. `failure` describes the required ordering for the load operation that takes place when the comparison fails. Using `Acquire` as success ordering makes the store part of this operation `Relaxed`, and using `Release` makes the successful load `Relaxed`. The failure ordering can only be `SeqCst`, `Acquire` or `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let some_var = AtomicI8::new(5);

    assert_eq!(some_var.compare_exchange(5, 10,
                                         Ordering::Acquire,
                                         Ordering::Relaxed),
               Ok(5));
    assert_eq!(some_var.load(Ordering::Relaxed), 10);

    assert_eq!(some_var.compare_exchange(6, 12,
                                         Ordering::SeqCst,
                                         Ordering::Acquire),
               Err(10));
    assert_eq!(some_var.load(Ordering::Relaxed), 10);

Run
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#### pub fn compare_exchange_weak( &self, current: i8, new: i8, success: Ordering, failure: Ordering ) -> Result<i8, i8>

Stores a value into the atomic integer if the current value is the same as the `current` value.

Unlike `AtomicI8::compare_exchange`, this function is allowed to spuriously fail even when the comparison succeeds, which can result in more efficient code on some platforms. The return value is a result indicating whether the new value was written and containing the previous value.

`compare_exchange_weak` takes two `Ordering` arguments to describe the memory ordering of this operation. `success` describes the required ordering for the read-modify-write operation that takes place if the comparison with `current` succeeds. `failure` describes the required ordering for the load operation that takes place when the comparison fails. Using `Acquire` as success ordering makes the store part of this operation `Relaxed`, and using `Release` makes the successful load `Relaxed`. The failure ordering can only be `SeqCst`, `Acquire` or `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let val = AtomicI8::new(4);

    let mut old = val.load(Ordering::Relaxed);
    loop {
        let new = old * 2;
        match val.compare_exchange_weak(old, new, Ordering::SeqCst, Ordering::Relaxed) {
            Ok(_) => break,
            Err(x) => old = x,
        }
    }

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#### pub fn fetch_add(&self, val: i8, order: Ordering) -> i8

Adds to the current value, returning the previous value.

This operation wraps around on overflow.

`fetch_add` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(0);
    assert_eq!(foo.fetch_add(10, Ordering::SeqCst), 0);
    assert_eq!(foo.load(Ordering::SeqCst), 10);

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#### pub fn fetch_sub(&self, val: i8, order: Ordering) -> i8

Subtracts from the current value, returning the previous value.

This operation wraps around on overflow.

`fetch_sub` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(20);
    assert_eq!(foo.fetch_sub(10, Ordering::SeqCst), 20);
    assert_eq!(foo.load(Ordering::SeqCst), 10);

Run
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#### pub fn fetch_and(&self, val: i8, order: Ordering) -> i8

Bitwise “and” with the current value.

Performs a bitwise “and” operation on the current value and the argument `val`, and sets the new value to the result.

Returns the previous value.

`fetch_and` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(0b101101);
    assert_eq!(foo.fetch_and(0b110011, Ordering::SeqCst), 0b101101);
    assert_eq!(foo.load(Ordering::SeqCst), 0b100001);

Run
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#### pub fn fetch_nand(&self, val: i8, order: Ordering) -> i8

Bitwise “nand” with the current value.

Performs a bitwise “nand” operation on the current value and the argument `val`, and sets the new value to the result.

Returns the previous value.

`fetch_nand` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(0x13);
    assert_eq!(foo.fetch_nand(0x31, Ordering::SeqCst), 0x13);
    assert_eq!(foo.load(Ordering::SeqCst), !(0x13 & 0x31));

Run
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#### pub fn fetch_or(&self, val: i8, order: Ordering) -> i8

Bitwise “or” with the current value.

Performs a bitwise “or” operation on the current value and the argument `val`, and sets the new value to the result.

Returns the previous value.

`fetch_or` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(0b101101);
    assert_eq!(foo.fetch_or(0b110011, Ordering::SeqCst), 0b101101);
    assert_eq!(foo.load(Ordering::SeqCst), 0b111111);

Run
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#### pub fn fetch_xor(&self, val: i8, order: Ordering) -> i8

Bitwise “xor” with the current value.

Performs a bitwise “xor” operation on the current value and the argument `val`, and sets the new value to the result.

Returns the previous value.

`fetch_xor` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(0b101101);
    assert_eq!(foo.fetch_xor(0b110011, Ordering::SeqCst), 0b101101);
    assert_eq!(foo.load(Ordering::SeqCst), 0b011110);

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1.45.0 · source

#### pub fn fetch_update<F>( &self, set_order: Ordering, fetch_order: Ordering, f: F ) -> Result<i8, i8>
where F: FnMut(i8) -> Option<i8>,

Fetches the value, and applies a function to it that returns an optional new value. Returns a `Result` of `Ok(previous_value)` if the function returned `Some(_)`, else `Err(previous_value)`.

Note: This may call the function multiple times if the value has been changed from other threads in the meantime, as long as the function returns `Some(_)`, but the function will have been applied only once to the stored value.

`fetch_update` takes two `Ordering` arguments to describe the memory ordering of this operation. The first describes the required ordering for when the operation finally succeeds while the second describes the required ordering for loads. These correspond to the success and failure orderings of `AtomicI8::compare_exchange` respectively.

Using `Acquire` as success ordering makes the store part of this operation `Relaxed`, and using `Release` makes the final successful load `Relaxed`. The (failed) load ordering can only be `SeqCst`, `Acquire` or `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Considerations

This method is not magic; it is not provided by the hardware. It is implemented in terms of `AtomicI8::compare_exchange_weak`, and suffers from the same drawbacks. In particular, this method will not circumvent the ABA Problem.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let x = AtomicI8::new(7);
    assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |_| None), Err(7));
    assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(x + 1)), Ok(7));
    assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(x + 1)), Ok(8));
    assert_eq!(x.load(Ordering::SeqCst), 9);

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1.45.0 · source

#### pub fn fetch_max(&self, val: i8, order: Ordering) -> i8

Maximum with the current value.

Finds the maximum of the current value and the argument `val`, and sets the new value to the result.

Returns the previous value.

`fetch_max` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(23);
    assert_eq!(foo.fetch_max(42, Ordering::SeqCst), 23);
    assert_eq!(foo.load(Ordering::SeqCst), 42);

Run

If you want to obtain the maximum value in one step, you can use the following:

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(23);
    let bar = 42;
    let max_foo = foo.fetch_max(bar, Ordering::SeqCst).max(bar);
    assert!(max_foo == 42);

Run
1.45.0 · source

#### pub fn fetch_min(&self, val: i8, order: Ordering) -> i8

Minimum with the current value.

Finds the minimum of the current value and the argument `val`, and sets the new value to the result.

Returns the previous value.

`fetch_min` takes an `Ordering` argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using `Acquire` makes the store part of this operation `Relaxed`, and using `Release` makes the load part `Relaxed`.

Note: This method is only available on platforms that support atomic operations on `i8`.

##### §Examples

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(23);
    assert_eq!(foo.fetch_min(42, Ordering::Relaxed), 23);
    assert_eq!(foo.load(Ordering::Relaxed), 23);
    assert_eq!(foo.fetch_min(22, Ordering::Relaxed), 23);
    assert_eq!(foo.load(Ordering::Relaxed), 22);

Run

If you want to obtain the minimum value in one step, you can use the following:

    use std::sync::atomic::{AtomicI8, Ordering};

    let foo = AtomicI8::new(23);
    let bar = 12;
    let min_foo = foo.fetch_min(bar, Ordering::SeqCst).min(bar);
    assert_eq!(min_foo, 12);

Run
1.70.0 (const: 1.70.0) · source

#### pub const fn as_ptr(&self) -> *mut i8

Returns a mutable pointer to the underlying integer.

Doing non-atomic reads and writes on the resulting integer can be a data race. This method is mostly useful for FFI, where the function signature may use `*mut i8` instead of `&AtomicI8`.

Returning an `*mut` pointer from a shared reference to this atomic is safe because the atomic types work with interior mutability. All modifications of an atomic change the value through a shared reference, and can do so safely as long as they use atomic operations. Any use of the returned raw pointer requires an `unsafe` block and still has to uphold the same restriction: operations on it must be atomic.

##### §Examples

ⓘ

    use std::sync::atomic::AtomicI8;

    extern "C" {
        fn my_atomic_op(arg: *mut i8);
    }

    let atomic = AtomicI8::new(1);

    // SAFETY: Safe as long as `my_atomic_op` is atomic.
    unsafe {
        my_atomic_op(atomic.as_ptr());
    }

Run

## Trait Implementations§

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### impl Debug for AtomicI8

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

Formats the value using the given formatter. Read more
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### impl Default for AtomicI8

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#### fn default() -> AtomicI8

Returns the “default value” for a type. Read more
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### impl From<i8> for AtomicI8

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#### fn from(v: i8) -> AtomicI8

Converts an `i8` into an `AtomicI8`.

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### impl RefUnwindSafe for AtomicI8

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### impl Sync for AtomicI8

## Auto Trait Implementations§

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### impl !Freeze for AtomicI8

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### impl Send for AtomicI8

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### impl Unpin for AtomicI8

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### impl UnwindSafe for AtomicI8

## Blanket Implementations§

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

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

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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

Returns the argument unchanged.

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

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

Calls `U::from(self)`.

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

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

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.