# Struct alloc::boxed::Box

1.0.0 · source ·

    pub struct Box<T: ?Sized, A: Allocator = Global>(_, _);

Expand description

A pointer type that uniquely owns a heap allocation of type `T`.

See the module-level documentation for more.

## Implementations§

source§

### impl<T> Box<T>

source

#### pub fn new(x: T) -> Self

Allocates memory on the heap and then places `x` into it.

This doesn’t actually allocate if `T` is zero-sized.

##### Examples

    let five = Box::new(5);

Run
source

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

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

Constructs a new box with uninitialized contents.

##### Examples

    #![feature(new_uninit)]

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

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

        five.assume_init()
    };

    assert_eq!(*five, 5)

Run
source

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

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

Constructs a new `Box` 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)]

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

    assert_eq!(*zero, 0)

Run
1.33.0 · source

#### pub fn pin(x: T) -> Pin<Box<T>>

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

Constructing and pinning of the `Box` can also be done in two steps: `Box::pin(x)` does the same as `Box::into_pin(Box::new(x))`. Consider using `into_pin` if you already have a `Box<T>`, or if you want to construct a (pinned) `Box` in a different way than with `Box::new`.

source

#### pub fn try_new(x: T) -> Result<Self, AllocError>

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

Allocates memory on the heap then places `x` into it, returning an error if the allocation fails

This doesn’t actually allocate if `T` is zero-sized.

##### Examples

    #![feature(allocator_api)]

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

Run
source

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

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

Constructs a new box with uninitialized contents on the heap, returning an error if the allocation fails

##### Examples

    #![feature(allocator_api, new_uninit)]

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

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

        five.assume_init()
    };

    assert_eq!(*five, 5);

Run
source

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

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

Constructs a new `Box` with uninitialized contents, with the memory being filled with `0` bytes on the heap

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

##### Examples

    #![feature(allocator_api, new_uninit)]

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

    assert_eq!(*zero, 0);

Run
source§

### impl<T, A: Allocator> Box<T, A>

source

#### pub fn new_in(x: T, alloc: A) -> Selfwhere A: Allocator,

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

Allocates memory in the given allocator then places `x` into it.

This doesn’t actually allocate if `T` is zero-sized.

##### Examples

    #![feature(allocator_api)]

    use std::alloc::System;

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

Run
source

#### pub fn try_new_in(x: T, alloc: A) -> Result<Self, AllocError>where A: Allocator,

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

Allocates memory in the given allocator then places `x` into it, returning an error if the allocation fails

This doesn’t actually allocate if `T` is zero-sized.

##### Examples

    #![feature(allocator_api)]

    use std::alloc::System;

    let five = Box::try_new_in(5, System)?;

Run
source

#### pub fn new_uninit_in(alloc: A) -> Box<MaybeUninit<T>, A>where A: Allocator,

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

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

##### Examples

    #![feature(allocator_api, new_uninit)]

    use std::alloc::System;

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

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

        five.assume_init()
    };

    assert_eq!(*five, 5)

Run
source

#### pub fn try_new_uninit_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where A: Allocator,

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

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

##### Examples

    #![feature(allocator_api, new_uninit)]

    use std::alloc::System;

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

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

        five.assume_init()
    };

    assert_eq!(*five, 5);

Run
source

#### pub fn new_zeroed_in(alloc: A) -> Box<MaybeUninit<T>, A>where A: Allocator,

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

Constructs a new `Box` 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_api, new_uninit)]

    use std::alloc::System;

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

    assert_eq!(*zero, 0)

Run
source

#### pub fn try_new_zeroed_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where A: Allocator,

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

Constructs a new `Box` 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_api, new_uninit)]

    use std::alloc::System;

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

    assert_eq!(*zero, 0);

Run
source

#### pub fn pin_in(x: T, alloc: A) -> Pin<Self>where A: 'static + Allocator,

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

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

Constructing and pinning of the `Box` can also be done in two steps: `Box::pin_in(x, alloc)` does the same as `Box::into_pin(Box::new_in(x, alloc))`. Consider using `into_pin` if you already have a `Box<T, A>`, or if you want to construct a (pinned) `Box` in a different way than with `Box::new_in`.

const: unstable · source

#### pub fn into_boxed_slice(boxed: Self) -> Box<[T], A>

🔬This is a nightly-only experimental API. (`box_into_boxed_slice` #71582)

Converts a `Box<T>` into a `Box<[T]>`

This conversion does not allocate on the heap and happens in place.

source

#### pub fn into_inner(boxed: Self) -> T

🔬This is a nightly-only experimental API. (`box_into_inner` #80437)

Consumes the `Box`, returning the wrapped value.

##### Examples

    #![feature(box_into_inner)]

    let c = Box::new(5);

    assert_eq!(Box::into_inner(c), 5);

Run
source§

### impl<T> Box<[T]>

source

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

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

Constructs a new boxed slice with uninitialized contents.

##### Examples

    #![feature(new_uninit)]

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

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

        values.assume_init()
    };

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

Run
source

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

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

Constructs a new boxed 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)]

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

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

Run
source

#### pub fn try_new_uninit_slice( len: usize ) -> Result<Box<[MaybeUninit<T>]>, AllocError>

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

Constructs a new boxed slice with uninitialized contents. Returns an error if the allocation fails

##### Examples

    #![feature(allocator_api, new_uninit)]

    let mut values = Box::<[u32]>::try_new_uninit_slice(3)?;
    let values = unsafe {
        // Deferred initialization:
        values[0].as_mut_ptr().write(1);
        values[1].as_mut_ptr().write(2);
        values[2].as_mut_ptr().write(3);
        values.assume_init()
    };

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

Run
source

#### pub fn try_new_zeroed_slice( len: usize ) -> Result<Box<[MaybeUninit<T>]>, AllocError>

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

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

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

##### Examples

    #![feature(allocator_api, new_uninit)]

    let values = Box::<[u32]>::try_new_zeroed_slice(3)?;
    let values = unsafe { values.assume_init() };

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

Run
source§

### impl<T, A: Allocator> Box<[T], A>

source

#### pub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[MaybeUninit<T>], A>

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

Constructs a new boxed slice with uninitialized contents in the provided allocator.

##### Examples

    #![feature(allocator_api, new_uninit)]

    use std::alloc::System;

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

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

        values.assume_init()
    };

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

Run
source

#### pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[MaybeUninit<T>], A>

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

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

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

##### Examples

    #![feature(allocator_api, new_uninit)]

    use std::alloc::System;

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

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

Run
source§

### impl<T, A: Allocator> Box<MaybeUninit<T>, A>

const: unstable · source

#### pub unsafe fn assume_init(self) -> Box<T, A>

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

Converts to `Box<T, A>`.

##### Safety

As with `MaybeUninit::assume_init`, it is up to the caller to guarantee that the 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)]

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

    let five: Box<u32> = unsafe {
        // Deferred initialization:
        five.as_mut_ptr().write(5);

        five.assume_init()
    };

    assert_eq!(*five, 5)

Run
const: unstable · source

#### pub fn write(boxed: Self, value: T) -> Box<T, A>

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

Writes the value and converts to `Box<T, A>`.

This method converts the box similarly to `Box::assume_init` but writes `value` into it before conversion thus guaranteeing safety. In some scenarios use of this method may improve performance because the compiler may be able to optimize copying from stack.

##### Examples

    #![feature(new_uninit)]

    let big_box = Box::<[usize; 1024]>::new_uninit();

    let mut array = [0; 1024];
    for (i, place) in array.iter_mut().enumerate() {
        *place = i;
    }

    // The optimizer may be able to elide this copy, so previous code writes
    // to heap directly.
    let big_box = Box::write(big_box, array);

    for (i, x) in big_box.iter().enumerate() {
        assert_eq!(*x, i);
    }

Run
source§

### impl<T, A: Allocator> Box<[MaybeUninit<T>], A>

source

#### pub unsafe fn assume_init(self) -> Box<[T], A>

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

Converts to `Box<[T], A>`.

##### Safety

As with `MaybeUninit::assume_init`, it is up to the caller to guarantee that the values really are in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.

##### Examples

    #![feature(new_uninit)]

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

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

        values.assume_init()
    };

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

Run
source§

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

1.4.0 · source

#### pub unsafe fn from_raw(raw: *mut T) -> Self

Constructs a box from a raw pointer.

After calling this function, the raw pointer is owned by the resulting `Box`. Specifically, the `Box` destructor will call the destructor of `T` and free the allocated memory. For this to be safe, the memory must have been allocated in accordance with the memory layout used by `Box` .

##### Safety

This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.

The safety conditions are described in the memory layout section.

##### Examples

Recreate a `Box` which was previously converted to a raw pointer using `Box::into_raw`:

    let x = Box::new(5);
    let ptr = Box::into_raw(x);
    let x = unsafe { Box::from_raw(ptr) };

Run

Manually create a `Box` from scratch by using the global allocator:

    use std::alloc::{alloc, Layout};

    unsafe {
        let ptr = alloc(Layout::new::<i32>()) as *mut i32;
        // In general .write is required to avoid attempting to destruct
        // the (uninitialized) previous contents of `ptr`, though for this
        // simple example `*ptr = 5` would have worked as well.
        ptr.write(5);
        let x = Box::from_raw(ptr);
    }

Run
source§

### impl<T: ?Sized, A: Allocator> Box<T, A>

const: unstable · source

#### pub unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Self

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

Constructs a box from a raw pointer in the given allocator.

After calling this function, the raw pointer is owned by the resulting `Box`. Specifically, the `Box` destructor will call the destructor of `T` and free the allocated memory. For this to be safe, the memory must have been allocated in accordance with the memory layout used by `Box` .

##### Safety

This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.

##### Examples

Recreate a `Box` which was previously converted to a raw pointer using `Box::into_raw_with_allocator`:

    #![feature(allocator_api)]

    use std::alloc::System;

    let x = Box::new_in(5, System);
    let (ptr, alloc) = Box::into_raw_with_allocator(x);
    let x = unsafe { Box::from_raw_in(ptr, alloc) };

Run

Manually create a `Box` from scratch by using the system allocator:

    #![feature(allocator_api, slice_ptr_get)]

    use std::alloc::{Allocator, Layout, System};

    unsafe {
        let ptr = System.allocate(Layout::new::<i32>())?.as_mut_ptr() as *mut i32;
        // In general .write is required to avoid attempting to destruct
        // the (uninitialized) previous contents of `ptr`, though for this
        // simple example `*ptr = 5` would have worked as well.
        ptr.write(5);
        let x = Box::from_raw_in(ptr, System);
    }

Run
1.4.0 · source

#### pub fn into_raw(b: Self) -> *mut T

Consumes the `Box`, returning a wrapped raw pointer.

The pointer will be properly aligned and non-null.

After calling this function, the caller is responsible for the memory previously managed by the `Box`. In particular, the caller should properly destroy `T` and release the memory, taking into account the memory layout used by `Box`. The easiest way to do this is to convert the raw pointer back into a `Box` with the `Box::from_raw` function, allowing the `Box` destructor to perform the cleanup.

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

##### Examples

Converting the raw pointer back into a `Box` with `Box::from_raw` for automatic cleanup:

    let x = Box::new(String::from("Hello"));
    let ptr = Box::into_raw(x);
    let x = unsafe { Box::from_raw(ptr) };

Run

Manual cleanup by explicitly running the destructor and deallocating the memory:

    use std::alloc::{dealloc, Layout};
    use std::ptr;

    let x = Box::new(String::from("Hello"));
    let p = Box::into_raw(x);
    unsafe {
        ptr::drop_in_place(p);
        dealloc(p as *mut u8, Layout::new::<String>());
    }

Run
const: unstable · source

#### pub fn into_raw_with_allocator(b: Self) -> (*mut T, A)

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

Consumes the `Box`, returning a wrapped raw pointer and the allocator.

The pointer will be properly aligned and non-null.

After calling this function, the caller is responsible for the memory previously managed by the `Box`. In particular, the caller should properly destroy `T` and release the memory, taking into account the memory layout used by `Box`. The easiest way to do this is to convert the raw pointer back into a `Box` with the `Box::from_raw_in` function, allowing the `Box` destructor to perform the cleanup.

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

##### Examples

Converting the raw pointer back into a `Box` with `Box::from_raw_in` for automatic cleanup:

    #![feature(allocator_api)]

    use std::alloc::System;

    let x = Box::new_in(String::from("Hello"), System);
    let (ptr, alloc) = Box::into_raw_with_allocator(x);
    let x = unsafe { Box::from_raw_in(ptr, alloc) };

Run

Manual cleanup by explicitly running the destructor and deallocating the memory:

    #![feature(allocator_api)]

    use std::alloc::{Allocator, Layout, System};
    use std::ptr::{self, NonNull};

    let x = Box::new_in(String::from("Hello"), System);
    let (ptr, alloc) = Box::into_raw_with_allocator(x);
    unsafe {
        ptr::drop_in_place(ptr);
        let non_null = NonNull::new_unchecked(ptr);
        alloc.deallocate(non_null.cast(), Layout::new::<String>());
    }

Run
const: unstable · source

#### pub fn allocator(b: &Self) -> &A

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

Returns a reference to the underlying allocator.

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

1.26.0 (const: unstable) · source

#### pub fn leak<'a>(b: Self) -> &'a mut T where A: 'a,

Consumes and leaks the `Box`, returning a mutable reference, `&'a mut T`. Note that the type `T` must outlive the chosen lifetime `'a`. If the type has only static references, or none at all, then this may be chosen to be `'static`.

This function is mainly useful for data that lives for the remainder of the program’s life. Dropping the returned reference will cause a memory leak. If this is not acceptable, the reference should first be wrapped with the `Box::from_raw` function producing a `Box`. This `Box` can then be dropped which will properly destroy `T` and release the allocated memory.

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

##### Examples

Simple usage:

    let x = Box::new(41);
    let static_ref: &'static mut usize = Box::leak(x);
    *static_ref += 1;
    assert_eq!(*static_ref, 42);

Run

Unsized data:

    let x = vec![1, 2, 3].into_boxed_slice();
    let static_ref = Box::leak(x);
    static_ref[0] = 4;
    assert_eq!(*static_ref, [4, 2, 3]);

Run
1.63.0 (const: unstable) · source

#### pub fn into_pin(boxed: Self) -> Pin<Self>where A: 'static,

Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement `Unpin`, then `*boxed` will be pinned in memory and unable to be moved.

This conversion does not allocate on the heap and happens in place.

This is also available via `From`.

Constructing and pinning a `Box` with `Box::into_pin(Box::new(x))` can also be written more concisely using `Box::pin(x)`. This `into_pin` method is useful if you already have a `Box<T>`, or you are constructing a (pinned) `Box` in a different way than with `Box::new`.

##### Notes

It’s not recommended that crates add an impl like `From<Box<T>> for Pin<T>`, as it’ll introduce an ambiguity when calling `Pin::from`. A demonstration of such a poor impl is shown below.

ⓘ

    struct Foo; // A type defined in this crate.
    impl From<Box<()>> for Pin<Foo> {
        fn from(_: Box<()>) -> Pin<Foo> {
            Pin::new(Foo)
        }
    }

    let foo = Box::new(());
    let bar = Pin::from(foo);

Run
source§

### impl<A: Allocator> Box<dyn Any, A>

source

#### pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self>

Attempt to downcast the box to a concrete type.

##### Examples

    use std::any::Any;

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

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

Run
source

#### pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A>

🔬This is a nightly-only experimental API. (`downcast_unchecked` #90850)

Downcasts the box to a concrete type.

For a safe alternative see `downcast`.

##### Examples

    #![feature(downcast_unchecked)]

    use std::any::Any;

    let x: Box<dyn Any> = Box::new(1_usize);

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

Run

##### Safety

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

source§

### impl<A: Allocator> Box<dyn Any + Send, A>

source

#### pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self>

Attempt to downcast the box to a concrete type.

##### Examples

    use std::any::Any;

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

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

Run
source

#### pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A>

🔬This is a nightly-only experimental API. (`downcast_unchecked` #90850)

Downcasts the box to a concrete type.

For a safe alternative see `downcast`.

##### Examples

    #![feature(downcast_unchecked)]

    use std::any::Any;

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

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

Run

##### Safety

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

source§

### impl<A: Allocator> Box<dyn Any + Send + Sync, A>

1.51.0 · source

#### pub fn downcast<T: Any>(self) -> Result<Box<T, A>, Self>

Attempt to downcast the box to a concrete type.

##### Examples

    use std::any::Any;

    fn print_if_string(value: Box<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(Box::new(my_string));
    print_if_string(Box::new(0i8));

Run
source

#### pub unsafe fn downcast_unchecked<T: Any>(self) -> Box<T, A>

🔬This is a nightly-only experimental API. (`downcast_unchecked` #90850)

Downcasts the box to a concrete type.

For a safe alternative see `downcast`.

##### Examples

    #![feature(downcast_unchecked)]

    use std::any::Any;

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

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

Run

##### Safety

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

## Trait Implementations§

1.5.0 · source§

### impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A>

source§

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

Converts this type into a mutable reference of the (usually inferred) input type.
1.5.0 · source§

### impl<T: ?Sized, A: Allocator> AsRef<T> for Box<T, A>

source§

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

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

### impl<S: ?Sized + AsyncIterator + Unpin> AsyncIterator for Box<S>

§

#### type Item = <S as AsyncIterator>::Item

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
The type of items yielded by the async iterator.
source§

#### fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<Self::Item>>

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
Attempt to pull out the next value of this async iterator, registering the current task for wakeup if the value is not yet available, and returning `None` if the async iterator is exhausted. Read more
source§

#### fn size_hint(&self) -> (usize, Option<usize>)

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
Returns the bounds on the remaining length of the async iterator. Read more
1.1.0 · source§

### impl<T: ?Sized, A: Allocator> Borrow<T> for Box<T, A>

source§

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

Immutably borrows from an owned value. Read more
1.1.0 · source§

### impl<T: ?Sized, A: Allocator> BorrowMut<T> for Box<T, A>

source§

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

Mutably borrows from an owned value. Read more
1.3.0 · source§

### impl<T: Clone, A: Allocator + Clone> Clone for Box<[T], A>

source§

#### fn clone(&self) -> Self

Returns a copy of the value. Read more
source§

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

Performs copy-assignment from `source`. Read more
1.29.0 · source§

### impl Clone for Box<CStr>

source§

#### fn clone(&self) -> Self

Returns a copy of the value. Read more
source§

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

Performs copy-assignment from `source`. Read more
source§

### impl<T: Clone, A: Allocator + Clone> Clone for Box<T, A>

source§

#### fn clone(&self) -> Self

Returns a new box with a `clone()` of this box’s contents.

##### Examples

    let x = Box::new(5);
    let y = x.clone();

    // The value is the same
    assert_eq!(x, y);

    // But they are unique objects
    assert_ne!(&*x as *const i32, &*y as *const i32);

Run
source§

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

Copies `source`’s contents into `self` without creating a new allocation.

##### Examples

    let x = Box::new(5);
    let mut y = Box::new(10);
    let yp: *const i32 = &*y;

    y.clone_from(&x);

    // The value is the same
    assert_eq!(x, y);

    // And no allocation occurred
    assert_eq!(yp, &*y);

Run
1.3.0 · source§

### impl Clone for Box<str>

source§

#### fn clone(&self) -> Self

Returns a copy of the value. Read more
source§

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

Performs copy-assignment from `source`. Read more
source§

### impl<T: Debug + ?Sized, A: Allocator> Debug for Box<T, A>

source§

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

Formats the value using the given formatter. Read more
const: unstable · source§

### impl<T> Default for Box<[T]>

const: unstable · source§

#### fn default() -> Self

Returns the “default value” for a type. Read more
1.17.0 · source§

### impl Default for Box<CStr>

source§

#### fn default() -> Box<CStr>

Returns the “default value” for a type. Read more
source§

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

source§

#### fn default() -> Self

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

1.17.0 (const: unstable) · source§

### impl Default for Box<str>

const: unstable · source§

#### fn default() -> Self

Returns the “default value” for a type. Read more
const: unstable · source§

### impl<T: ?Sized, A: Allocator> Deref for Box<T, A>

§

#### type Target = T

The resulting type after dereferencing.
const: unstable · source§

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

Dereferences the value.
const: unstable · source§

### impl<T: ?Sized, A: Allocator> DerefMut for Box<T, A>

const: unstable · source§

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

Mutably dereferences the value.
source§

### impl<T: Display + ?Sized, A: Allocator> Display for Box<T, A>

source§

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

Formats the value using the given formatter. Read more
source§

### impl<I: DoubleEndedIterator + ?Sized, A: Allocator> DoubleEndedIterator for Box<I, A>

source§

#### fn next_back(&mut self) -> Option<I::Item>

Removes and returns an element from the end of the iterator. Read more
source§

#### fn nth_back(&mut self, n: usize) -> Option<I::Item>

Returns the `n`th element from the end of the iterator. Read more
source§

#### fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize>

🔬This is a nightly-only experimental API. (`iter_advance_by` #77404)
Advances the iterator from the back by `n` elements. Read more
1.27.0 · source§

#### fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> Rwhere Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Output = B>,

This is the reverse version of `Iterator::try_fold()`: it takes elements starting from the back of the iterator. Read more
1.27.0 · source§

#### fn rfold<B, F>(self, init: B, f: F) -> Bwhere Self: Sized, F: FnMut(B, Self::Item) -> B,

An iterator method that reduces the iterator’s elements to a single, final value, starting from the back. Read more
1.27.0 · source§

#### fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator from the back that satisfies a predicate. Read more
source§

### impl<T: ?Sized, A: Allocator> Drop for Box<T, A>

source§

#### fn drop(&mut self)

Executes the destructor for this type. Read more
1.8.0 · source§

### impl<T: Error> Error for Box<T>

source§

#### fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()
Read more
source§

#### fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
source§

#### fn source(&self) -> Option<&(dyn Error + 'static)>

The lower-level source of this error, if any. Read more
source§

#### fn provide<'a>(&'a self, demand: &mut Demand<'a>)

🔬This is a nightly-only experimental API. (`error_generic_member_access` #99301)
Provides type based access to context intended for error reports. Read more
source§

### impl<I: ExactSizeIterator + ?Sized, A: Allocator> ExactSizeIterator for Box<I, A>

source§

#### fn len(&self) -> usize

Returns the exact remaining length of the iterator. Read more
source§

#### fn is_empty(&self) -> bool

🔬This is a nightly-only experimental API. (`exact_size_is_empty` #35428)
Returns `true` if the iterator is empty. Read more
1.45.0 · source§

### impl Extend<Box<str, Global>> for String

source§

#### fn extend<I: IntoIterator<Item = Box<str>>>(&mut self, iter: I)

Extends a collection with the contents of an iterator. Read more
source§

#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.35.0 · source§

### impl<Args: Tuple, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A>

source§

#### extern "rust-call" fn call(&self, args: Args) -> Self::Output

🔬This is a nightly-only experimental API. (`fn_traits` #29625)
Performs the call operation.
1.35.0 · source§

### impl<Args: Tuple, F: FnMut<Args> + ?Sized, A: Allocator> FnMut<Args> for Box<F, A>

source§

#### extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output

🔬This is a nightly-only experimental API. (`fn_traits` #29625)
Performs the call operation.
1.35.0 · source§

### impl<Args: Tuple, F: FnOnce<Args> + ?Sized, A: Allocator> FnOnce<Args> for Box<F, A>

§

#### type Output = <F as FnOnce<Args>>::Output

The returned type after the call operator is used.
source§

#### extern "rust-call" fn call_once(self, args: Args) -> Self::Output

🔬This is a nightly-only experimental API. (`fn_traits` #29625)
Performs the call operation.
1.17.0 · source§

### impl<T: Copy> From<&[T]> for Box<[T]>

source§

#### fn from(slice: &[T]) -> Box<[T]>

Converts a `&[T]` into a `Box<[T]>`

This conversion allocates on the heap and performs a copy of `slice` and its contents.

##### Examples

    // create a &[u8] which will be used to create a Box<[u8]>
    let slice: &[u8] = &[104, 101, 108, 108, 111];
    let boxed_slice: Box<[u8]> = Box::from(slice);

    println!("{boxed_slice:?}");

Run
1.17.0 · source§

### impl From<&CStr> for Box<CStr>

source§

#### fn from(s: &CStr) -> Box<CStr>

Converts a `&CStr` into a `Box<CStr>`, by copying the contents into a newly allocated `Box`.

1.6.0 · source§

### impl From<&str> for Box<dyn Error>

source§

#### fn from(err: &str) -> Box<dyn Error>

Converts a `str` into a box of dyn `Error`.

##### Examples

    use std::error::Error;
    use std::mem;

    let a_str_error = "a str error";
    let a_boxed_error = Box::<dyn Error>::from(a_str_error);
    assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

Run
source§

### impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a>

source§

#### fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a>

Converts a `str` into a box of dyn `Error` + `Send` + `Sync`.

##### Examples

    use std::error::Error;
    use std::mem;

    let a_str_error = "a str error";
    let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
    assert!(
        mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Run
1.17.0 · source§

### impl From<&str> for Box<str>

source§

#### fn from(s: &str) -> Box<str>

Converts a `&str` into a `Box<str>`

This conversion allocates on the heap and performs a copy of `s`.

##### Examples

    let boxed: Box<str> = Box::from("hello");
    println!("{boxed}");

Run
1.45.0 · source§

### impl<T, const N: usize> From<[T; N]> for Box<[T]>

source§

#### fn from(array: [T; N]) -> Box<[T]>

Converts a `[T; N]` into a `Box<[T]>`

This conversion moves the array to newly heap-allocated memory.

##### Examples

    let boxed: Box<[u8]> = Box::from([4, 2]);
    println!("{boxed:?}");

Run
1.18.0 · source§

### impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A>

source§

#### fn from(s: Box<[T], A>) -> Self

Convert a boxed slice into a vector by transferring ownership of the existing heap allocation.

##### Examples

    let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
    assert_eq!(Vec::from(b), vec![1, 2, 3]);

Run
1.18.0 · source§

### impl From<Box<CStr, Global>> for CString

source§

#### fn from(s: Box<CStr>) -> CString

Converts a `Box<CStr>` into a `CString` without copying or allocating.

1.33.0 (const: unstable) · source§

### impl<T: ?Sized, A> From<Box<T, A>> for Pin<Box<T, A>>where A: 'static + Allocator,

const: unstable · source§

#### fn from(boxed: Box<T, A>) -> Self

Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement `Unpin`, then `*boxed` will be pinned in memory and unable to be moved.

This conversion does not allocate on the heap and happens in place.

This is also available via `Box::into_pin`.

Constructing and pinning a `Box` with `<Pin<Box<T>>>::from(Box::new(x))` can also be written more concisely using `Box::pin(x)`. This `From` implementation is useful if you already have a `Box<T>`, or you are constructing a (pinned) `Box` in a different way than with `Box::new`.

1.21.0 · source§

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

source§

#### 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
1.21.0 · source§

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

source§

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

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

##### Example

    let original: Box<i32> = Box::new(1);
    let shared: Rc<i32> = Rc::from(original);
    assert_eq!(1, *shared);

Run
1.19.0 · source§

### impl<A: Allocator> From<Box<str, A>> for Box<[u8], A>

source§

#### fn from(s: Box<str, A>) -> Self

Converts a `Box<str>` into a `Box<[u8]>`

This conversion does not allocate on the heap and happens in place.

##### Examples

    // create a Box<str> which will be used to create a Box<[u8]>
    let boxed: Box<str> = Box::from("hello");
    let boxed_str: Box<[u8]> = Box::from(boxed);

    // create a &[u8] which will be used to create a Box<[u8]>
    let slice: &[u8] = &[104, 101, 108, 108, 111];
    let boxed_slice = Box::from(slice);

    assert_eq!(boxed_slice, boxed_str);

Run
1.18.0 · source§

### impl From<Box<str, Global>> for String

source§

#### fn from(s: Box<str>) -> String

Converts the given boxed `str` slice to a `String`. It is notable that the `str` slice is owned.

##### Examples

Basic usage:

    let s1: String = String::from("hello world");
    let s2: Box<str> = s1.into_boxed_str();
    let s3: String = String::from(s2);

    assert_eq!("hello world", s3)

Run
1.20.0 · source§

### impl From<CString> for Box<CStr>

source§

#### fn from(s: CString) -> Box<CStr>

Converts a `CString` into a `Box<CStr>` without copying or allocating.

1.45.0 · source§

### impl<T: Copy> From<Cow<'_, [T]>> for Box<[T]>

source§

#### fn from(cow: Cow<'_, [T]>) -> Box<[T]>

Converts a `Cow<'_, [T]>` into a `Box<[T]>`

When `cow` is the `Cow::Borrowed` variant, this conversion allocates on the heap and copies the underlying slice. Otherwise, it will try to reuse the owned `Vec`’s allocation.

1.45.0 · source§

### impl From<Cow<'_, CStr>> for Box<CStr>

source§

#### fn from(cow: Cow<'_, CStr>) -> Box<CStr>

Converts a `Cow<'a, CStr>` into a `Box<CStr>`, by copying the contents if they are borrowed.

1.45.0 · source§

### impl From<Cow<'_, str>> for Box<str>

source§

#### fn from(cow: Cow<'_, str>) -> Box<str>

Converts a `Cow<'_, str>` into a `Box<str>`

When `cow` is the `Cow::Borrowed` variant, this conversion allocates on the heap and copies the underlying `str`. Otherwise, it will try to reuse the owned `String`’s allocation.

##### Examples

    use std::borrow::Cow;

    let unboxed = Cow::Borrowed("hello");
    let boxed: Box<str> = Box::from(unboxed);
    println!("{boxed}");

Run

    let unboxed = Cow::Owned("hello".to_string());
    let boxed: Box<str> = Box::from(unboxed);
    println!("{boxed}");

Run
1.22.0 · source§

### impl<'a> From<Cow<'a, str>> for Box<dyn Error>

source§

#### fn from(err: Cow<'a, str>) -> Box<dyn Error>

Converts a `Cow` into a box of dyn `Error`.

##### Examples

    use std::error::Error;
    use std::mem;
    use std::borrow::Cow;

    let a_cow_str_error = Cow::from("a str error");
    let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
    assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

Run
1.22.0 · source§

### impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a>

source§

#### fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a>

Converts a `Cow` into a box of dyn `Error` + `Send` + `Sync`.

##### Examples

    use std::error::Error;
    use std::mem;
    use std::borrow::Cow;

    let a_cow_str_error = Cow::from("a str error");
    let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
    assert!(
        mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Run
source§

### impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a>

source§

#### fn from(err: E) -> Box<dyn Error + 'a>

Converts a type of `Error` into a box of dyn `Error`.

##### Examples

    use std::error::Error;
    use std::fmt;
    use std::mem;

    #[derive(Debug)]
    struct AnError;

    impl fmt::Display for AnError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "An error")
        }
    }

    impl Error for AnError {}

    let an_error = AnError;
    assert!(0 == mem::size_of_val(&an_error));
    let a_boxed_error = Box::<dyn Error>::from(an_error);
    assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

Run
source§

### impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a>

source§

#### fn from(err: E) -> Box<dyn Error + Send + Sync + 'a>

Converts a type of `Error` + `Send` + `Sync` into a box of dyn `Error` + `Send` + `Sync`.

##### Examples

    use std::error::Error;
    use std::fmt;
    use std::mem;

    #[derive(Debug)]
    struct AnError;

    impl fmt::Display for AnError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "An error")
        }
    }

    impl Error for AnError {}

    unsafe impl Send for AnError {}

    unsafe impl Sync for AnError {}

    let an_error = AnError;
    assert!(0 == mem::size_of_val(&an_error));
    let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
    assert!(
        mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Run
1.6.0 · source§

### impl From<String> for Box<dyn Error>

source§

#### fn from(str_err: String) -> Box<dyn Error>

Converts a `String` into a box of dyn `Error`.

##### Examples

    use std::error::Error;
    use std::mem;

    let a_string_error = "a string error".to_string();
    let a_boxed_error = Box::<dyn Error>::from(a_string_error);
    assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

Run
source§

### impl From<String> for Box<dyn Error + Send + Sync>

source§

#### fn from(err: String) -> Box<dyn Error + Send + Sync>

Converts a `String` into a box of dyn `Error` + `Send` + `Sync`.

##### Examples

    use std::error::Error;
    use std::mem;

    let a_string_error = "a string error".to_string();
    let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
    assert!(
        mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Run
1.20.0 · source§

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

source§

#### fn from(s: String) -> Box<str>

Converts the given `String` to a boxed `str` slice that is owned.

##### Examples

Basic usage:

    let s1: String = String::from("hello world");
    let s2: Box<str> = Box::from(s1);
    let s3: String = String::from(s2);

    assert_eq!("hello world", s3)

Run
1.6.0 · source§

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

source§

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

Converts a `T` into a `Box<T>`

The conversion allocates on the heap and moves `t` from the stack into it.

##### Examples

    let x = 5;
    let boxed = Box::new(5);

    assert_eq!(Box::from(x), boxed);

Run
1.20.0 · source§

### impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A>

source§

#### fn from(v: Vec<T, A>) -> Self

Convert a vector into a boxed slice.

If `v` has excess capacity, its items will be moved into a newly-allocated buffer with exactly the right capacity.

##### Examples

    assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());

Run

Any excess capacity is removed:

    let mut vec = Vec::with_capacity(10);
    vec.extend([1, 2, 3]);

    assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());

Run
1.45.0 · source§

### impl FromIterator<Box<str, Global>> for String

source§

#### fn from_iter<I: IntoIterator<Item = Box<str>>>(iter: I) -> String

Creates a value from an iterator. Read more
1.32.0 · source§

### impl<I> FromIterator<I> for Box<[I]>

source§

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

Creates a value from an iterator. Read more
1.36.0 · source§

### impl<F: ?Sized + Future + Unpin, A> Future for Box<F, A>where A: 'static + Allocator,

§

#### type Output = <F as Future>::Output

The type of value produced on completion.
source§

#### fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more
source§

### impl<G: ?Sized + Generator<R> + Unpin, R, A> Generator<R> for Box<G, A>where A: 'static + Allocator,

§

#### type Yield = <G as Generator<R>>::Yield

🔬This is a nightly-only experimental API. (`generator_trait` #43122)
The type of value this generator yields. Read more
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#### type Return = <G as Generator<R>>::Return

🔬This is a nightly-only experimental API. (`generator_trait` #43122)
The type of value this generator returns. Read more
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#### fn resume( self: Pin<&mut Self>, arg: R ) -> GeneratorState<Self::Yield, Self::Return>

🔬This is a nightly-only experimental API. (`generator_trait` #43122)
Resumes the execution of this generator. Read more
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### impl<G: ?Sized + Generator<R>, R, A> Generator<R> for Pin<Box<G, A>>where A: 'static + Allocator,

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#### type Yield = <G as Generator<R>>::Yield

🔬This is a nightly-only experimental API. (`generator_trait` #43122)
The type of value this generator yields. Read more
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#### type Return = <G as Generator<R>>::Return

🔬This is a nightly-only experimental API. (`generator_trait` #43122)
The type of value this generator returns. Read more
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#### fn resume( self: Pin<&mut Self>, arg: R ) -> GeneratorState<Self::Yield, Self::Return>

🔬This is a nightly-only experimental API. (`generator_trait` #43122)
Resumes the execution of this generator. Read more
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### impl<T: ?Sized + Hash, A: Allocator> Hash for Box<T, A>

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

Feeds this value into the given `Hasher`. Read more
1.3.0 · source§

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

Feeds a slice of this type into the given `Hasher`. Read more
1.22.0 · source§

### impl<T: ?Sized + Hasher, A: Allocator> Hasher for Box<T, A>

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#### fn finish(&self) -> u64

Returns the hash value for the values written so far. Read more
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#### fn write(&mut self, bytes: &[u8])

Writes some data into this `Hasher`. Read more
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#### fn write_u8(&mut self, i: u8)

Writes a single `u8` into this hasher.
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#### fn write_u16(&mut self, i: u16)

Writes a single `u16` into this hasher.
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#### fn write_u32(&mut self, i: u32)

Writes a single `u32` into this hasher.
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#### fn write_u64(&mut self, i: u64)

Writes a single `u64` into this hasher.
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#### fn write_u128(&mut self, i: u128)

Writes a single `u128` into this hasher.
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#### fn write_usize(&mut self, i: usize)

Writes a single `usize` into this hasher.
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#### fn write_i8(&mut self, i: i8)

Writes a single `i8` into this hasher.
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#### fn write_i16(&mut self, i: i16)

Writes a single `i16` into this hasher.
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#### fn write_i32(&mut self, i: i32)

Writes a single `i32` into this hasher.
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#### fn write_i64(&mut self, i: i64)

Writes a single `i64` into this hasher.
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#### fn write_i128(&mut self, i: i128)

Writes a single `i128` into this hasher.
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#### fn write_isize(&mut self, i: isize)

Writes a single `isize` into this hasher.
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#### fn write_length_prefix(&mut self, len: usize)

🔬This is a nightly-only experimental API. (`hasher_prefixfree_extras` #96762)
Writes a length prefix into this hasher, as part of being prefix-free. Read more
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#### fn write_str(&mut self, s: &str)

🔬This is a nightly-only experimental API. (`hasher_prefixfree_extras` #96762)
Writes a single `str` into this hasher. Read more
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### impl<I: Iterator + ?Sized, A: Allocator> Iterator for Box<I, A>

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#### type Item = <I as Iterator>::Item

The type of the elements being iterated over.
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#### fn next(&mut self) -> Option<I::Item>

Advances the iterator and returns the next value. Read more
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#### fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the iterator. Read more
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#### fn nth(&mut self, n: usize) -> Option<I::Item>

Returns the `n`th element of the iterator. Read more
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#### fn last(self) -> Option<I::Item>

Consumes the iterator, returning the last element. Read more
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#### fn next_chunk<const N: usize>( &mut self ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where Self: Sized,

🔬This is a nightly-only experimental API. (`iter_next_chunk` #98326)
Advances the iterator and returns an array containing the next `N` values. Read more
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#### fn count(self) -> usize where Self: Sized,

Consumes the iterator, counting the number of iterations and returning it. Read more
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#### fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize>

🔬This is a nightly-only experimental API. (`iter_advance_by` #77404)
Advances the iterator by `n` elements. Read more
1.28.0 · source§

#### fn step_by(self, step: usize) -> StepBy<Self>where Self: Sized,

Creates an iterator starting at the same point, but stepping by the given amount at each iteration. Read more
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#### fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter>where Self: Sized, U: IntoIterator<Item = Self::Item>,

Takes two iterators and creates a new iterator over both in sequence. Read more
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#### fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter>where Self: Sized, U: IntoIterator,

‘Zips up’ two iterators into a single iterator of pairs. Read more
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#### fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>where Self: Sized, G: FnMut() -> Self::Item,

🔬This is a nightly-only experimental API. (`iter_intersperse` #79524)
Creates a new iterator which places an item generated by `separator` between adjacent items of the original iterator. Read more
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#### fn map<B, F>(self, f: F) -> Map<Self, F>where Self: Sized, F: FnMut(Self::Item) -> B,

Takes a closure and creates an iterator which calls that closure on each element. Read more
1.21.0 · source§

#### fn for_each<F>(self, f: F)where Self: Sized, F: FnMut(Self::Item),

Calls a closure on each element of an iterator. Read more
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#### fn filter<P>(self, predicate: P) -> Filter<Self, P>where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator which uses a closure to determine if an element should be yielded. Read more
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#### fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both filters and maps. Read more
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#### fn enumerate(self) -> Enumerate<Self>where Self: Sized,

Creates an iterator which gives the current iteration count as well as the next value. Read more
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#### fn peekable(self) -> Peekable<Self>where Self: Sized,

Creates an iterator which can use the `peek` and `peek_mut` methods to look at the next element of the iterator without consuming it. See their documentation for more information. Read more
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#### fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that `skip`s elements based on a predicate. Read more
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#### fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate. Read more
1.57.0 · source§

#### fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P>where Self: Sized, P: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both yields elements based on a predicate and maps. Read more
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#### fn skip(self, n: usize) -> Skip<Self>where Self: Sized,

Creates an iterator that skips the first `n` elements. Read more
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#### fn take(self, n: usize) -> Take<Self>where Self: Sized,

Creates an iterator that yields the first `n` elements, or fewer if the underlying iterator ends sooner. Read more
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#### fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,

An iterator adapter which, like `fold`, holds internal state, but unlike `fold`, produces a new iterator. Read more
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#### fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,

Creates an iterator that works like map, but flattens nested structure. Read more
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#### fn fuse(self) -> Fuse<Self>where Self: Sized,

Creates an iterator which ends after the first `None`. Read more
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#### fn inspect<F>(self, f: F) -> Inspect<Self, F>where Self: Sized, F: FnMut(&Self::Item),

Does something with each element of an iterator, passing the value on. Read more
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#### fn by_ref(&mut self) -> &mut Self where Self: Sized,

Borrows an iterator, rather than consuming it. Read more
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#### fn collect<B>(self) -> Bwhere B: FromIterator<Self::Item>, Self: Sized,

Transforms an iterator into a collection. Read more
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#### fn collect_into<E>(self, collection: &mut E) -> &mut E where E: Extend<Self::Item>, Self: Sized,

🔬This is a nightly-only experimental API. (`iter_collect_into` #94780)
Collects all the items from an iterator into a collection. Read more
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#### fn partition<B, F>(self, f: F) -> (B, B)where Self: Sized, B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool,

Consumes an iterator, creating two collections from it. Read more
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#### fn is_partitioned<P>(self, predicate: P) -> bool where Self: Sized, P: FnMut(Self::Item) -> bool,

🔬This is a nightly-only experimental API. (`iter_is_partitioned` #62544)
Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return `true` precede all those that return `false`. Read more
1.27.0 · source§

#### fn try_fold<B, F, R>(&mut self, init: B, f: F) -> Rwhere Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Output = B>,

An iterator method that applies a function as long as it returns successfully, producing a single, final value. Read more
1.27.0 · source§

#### fn try_for_each<F, R>(&mut self, f: F) -> Rwhere Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Output = ()>,

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error. Read more
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#### fn fold<B, F>(self, init: B, f: F) -> Bwhere Self: Sized, F: FnMut(B, Self::Item) -> B,

Folds every element into an accumulator by applying an operation, returning the final result. Read more
1.51.0 · source§

#### fn reduce<F>(self, f: F) -> Option<Self::Item>where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item,

Reduces the elements to a single one, by repeatedly applying a reducing operation. Read more
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#### fn try_reduce<F, R>( &mut self, f: F ) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType where Self: Sized, F: FnMut(Self::Item, Self::Item) -> R, R: Try<Output = Self::Item>, <R as Try>::Residual: Residual<Option<Self::Item>>,

🔬This is a nightly-only experimental API. (`iterator_try_reduce` #87053)
Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately. Read more
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#### fn all<F>(&mut self, f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if every element of the iterator matches a predicate. Read more
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#### fn any<F>(&mut self, f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if any element of the iterator matches a predicate. Read more
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#### fn find<P>(&mut self, predicate: P) -> Option<Self::Item>where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator that satisfies a predicate. Read more
1.30.0 · source§

#### fn find_map<B, F>(&mut self, f: F) -> Option<B>where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Applies function to the elements of iterator and returns the first non-none result. Read more
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#### fn try_find<F, R>( &mut self, f: F ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType where Self: Sized, F: FnMut(&Self::Item) -> R, R: Try<Output = bool>, <R as Try>::Residual: Residual<Option<Self::Item>>,

🔬This is a nightly-only experimental API. (`try_find` #63178)
Applies function to the elements of iterator and returns the first true result or the first error. Read more
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#### fn position<P>(&mut self, predicate: P) -> Option<usize>where Self: Sized, P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator, returning its index. Read more
1.6.0 · source§

#### fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the maximum value from the specified function. Read more
1.15.0 · source§

#### fn max_by<F>(self, compare: F) -> Option<Self::Item>where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the maximum value with respect to the specified comparison function. Read more
1.6.0 · source§

#### fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the minimum value from the specified function. Read more
1.15.0 · source§

#### fn min_by<F>(self, compare: F) -> Option<Self::Item>where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the minimum value with respect to the specified comparison function. Read more
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#### fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Iterator<Item = (A, B)>,

Converts an iterator of pairs into a pair of containers. Read more
1.36.0 · source§

#### fn copied<'a, T>(self) -> Copied<Self>where T: 'a + Copy, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which copies all of its elements. Read more
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#### fn cloned<'a, T>(self) -> Cloned<Self>where T: 'a + Clone, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which `clone`s all of its elements. Read more
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#### fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>where Self: Sized,

🔬This is a nightly-only experimental API. (`iter_array_chunks` #100450)
Returns an iterator over `N` elements of the iterator at a time. Read more
1.11.0 · source§

#### fn sum<S>(self) -> Swhere Self: Sized, S: Sum<Self::Item>,

Sums the elements of an iterator. Read more
1.11.0 · source§

#### fn product<P>(self) -> Pwhere Self: Sized, P: Product<Self::Item>,

Iterates over the entire iterator, multiplying all the elements Read more
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#### fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,

🔬This is a nightly-only experimental API. (`iter_order_by` #64295)
Lexicographically compares the elements of this `Iterator` with those of another with respect to the specified comparison function. Read more
1.5.0 · source§

#### fn partial_cmp<I>(self, other: I) -> Option<Ordering>where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Lexicographically compares the `PartialOrd` elements of this `Iterator` with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned. Read more
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#### fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (`iter_order_by` #64295)
Lexicographically compares the elements of this `Iterator` with those of another with respect to the specified comparison function. Read more
1.5.0 · source§

#### fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are equal to those of another. Read more
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#### fn eq_by<I, F>(self, other: I, eq: F) -> bool where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,

🔬This is a nightly-only experimental API. (`iter_order_by` #64295)
Determines if the elements of this `Iterator` are equal to those of another with respect to the specified equality function. Read more
1.5.0 · source§

#### fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are not equal to those of another. Read more
1.5.0 · source§

#### fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically less than those of another. Read more
1.5.0 · source§

#### fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically less or equal to those of another. Read more
1.5.0 · source§

#### fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically greater than those of another. Read more
1.5.0 · source§

#### fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically greater than or equal to those of another. Read more
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#### fn is_sorted_by<F>(self, compare: F) -> bool where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (`is_sorted` #53485)
Checks if the elements of this iterator are sorted using the given comparator function. Read more
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#### fn is_sorted_by_key<F, K>(self, f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> K, K: PartialOrd<K>,

🔬This is a nightly-only experimental API. (`is_sorted` #53485)
Checks if the elements of this iterator are sorted using the given key extraction function. Read more
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### impl<T: ?Sized + Ord, A: Allocator> Ord for Box<T, A>

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#### fn cmp(&self, other: &Self) -> Ordering

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · source§

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

Compares and returns the maximum of two values. Read more
1.21.0 · source§

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

Compares and returns the minimum of two values. Read more
1.50.0 · source§

#### fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval. Read more
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### impl<T: ?Sized + PartialEq, A: Allocator> PartialEq<Box<T, A>> for Box<T, A>

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#### fn eq(&self, other: &Self) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Self) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl<T: ?Sized + PartialOrd, A: Allocator> PartialOrd<Box<T, A>> for Box<T, A>

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

This method returns an ordering between `self` and `other` values if one exists. Read more
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#### fn lt(&self, other: &Self) -> bool

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more
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#### fn le(&self, other: &Self) -> bool

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
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#### fn ge(&self, other: &Self) -> bool

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
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#### fn gt(&self, other: &Self) -> bool

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
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### impl<T: ?Sized, A: Allocator> Pointer for Box<T, A>

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

Formats the value using the given formatter.
1.43.0 · source§

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

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

Attempts to convert a `Box<[T]>` into a `Box<[T; N]>`.

The conversion occurs in-place and does not require a new memory allocation.

##### Errors

Returns the old `Box<[T]>` in the `Err` variant if `boxed_slice.len()` does not equal `N`.

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#### type Error = Box<[T], Global>

The type returned in the event of a conversion error.
1.66.0 · source§

### impl<T, const N: usize> TryFrom<Vec<T, Global>> for Box<[T; N]>

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#### fn try_from(vec: Vec<T>) -> Result<Self, Self::Error>

Attempts to convert a `Vec<T>` into a `Box<[T; N]>`.

Like `Vec::into_boxed_slice`, this is in-place if `vec.capacity() == N`, but will require a reallocation otherwise.

##### Errors

Returns the original `Vec<T>` in the `Err` variant if `boxed_slice.len()` does not equal `N`.

##### Examples

This can be used with `vec!` to create an array on the heap:

    let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap();
    assert_eq!(state.len(), 100);

Run
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#### type Error = Vec<T, Global>

The type returned in the event of a conversion error.
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### impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<Box<U, A>> for Box<T, A>

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

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### impl<T: ?Sized + Eq, A: Allocator> Eq for Box<T, A>

1.26.0 · source§

### impl<I: FusedIterator + ?Sized, A: Allocator> FusedIterator for Box<I, A>

1.33.0 · source§

### impl<T: ?Sized, A> Unpin for Box<T, A>where A: 'static + Allocator,

## Auto Trait Implementations§

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

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### impl<T: ?Sized, A> Send for Box<T, A>where A: Send, T: Send,

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### impl<T: ?Sized, A> Sync for Box<T, A>where A: Sync, T: Sync,

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### impl<T: ?Sized, A> UnwindSafe for Box<T, A>where A: UnwindSafe, T: UnwindSafe,

## Blanket Implementations§

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

source§

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

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

const: unstable · source§

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

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

const: unstable · source§

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

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

const: unstable · source§

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

Converts to this type from the input type.
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### impl<T> From<T> for T

const: unstable · source§

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

Returns the argument unchanged.

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

const: unstable · source§

#### 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<F> IntoFuture for Fwhere F: Future,

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#### type Output = <F as Future>::Output

The output that the future will produce on completion.
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#### type IntoFuture = F

Which kind of future are we turning this into?
source§

#### fn into_future(self) -> <F as IntoFuture>::IntoFuture

Creates a future from a value. Read more
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### impl<I> IntoIterator for Iwhere I: Iterator,

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#### type Item = <I as Iterator>::Item

The type of the elements being iterated over.
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#### type IntoIter = I

Which kind of iterator are we turning this into?
const: unstable · source§

#### fn into_iter(self) -> I

Creates an iterator from a value. Read more
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### impl<'a, F> Pattern<'a> for Fwhere F: FnMut(char) -> bool,

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#### type Searcher = CharPredicateSearcher<'a, F>

🔬This is a nightly-only experimental API. (`pattern` #27721)
Associated searcher for this pattern
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#### fn into_searcher(self, haystack: &'a str) -> CharPredicateSearcher<'a, F>

🔬This is a nightly-only experimental API. (`pattern` #27721)
Constructs the associated searcher from `self` and the `haystack` to search in.
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#### fn is_contained_in(self, haystack: &'a str) -> bool

🔬This is a nightly-only experimental API. (`pattern` #27721)
Checks whether the pattern matches anywhere in the haystack
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#### fn is_prefix_of(self, haystack: &'a str) -> bool

🔬This is a nightly-only experimental API. (`pattern` #27721)
Checks whether the pattern matches at the front of the haystack
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#### fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str>

🔬This is a nightly-only experimental API. (`pattern` #27721)
Removes the pattern from the front of haystack, if it matches.
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#### fn is_suffix_of(self, haystack: &'a str) -> bool where CharPredicateSearcher<'a, F>: ReverseSearcher<'a>,

🔬This is a nightly-only experimental API. (`pattern` #27721)
Checks whether the pattern matches at the back of the haystack
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#### fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>where CharPredicateSearcher<'a, F>: ReverseSearcher<'a>,

🔬This is a nightly-only experimental API. (`pattern` #27721)
Removes the pattern from the back of haystack, if it matches.
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### impl<E> Provider for Ewhere E: Error + ?Sized,

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#### fn provide<'a>(&'a self, demand: &mut Demand<'a>)

🔬This is a nightly-only experimental API. (`provide_any` #96024)
Data providers should implement this method to provide all values they are able to provide by using `demand`. Read more
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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T> ToString for Twhere T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

#### 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 Twhere U: TryFrom<T>,

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

The type returned in the event of a conversion error.
const: unstable · source§

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

Performs the conversion.