# Struct Box

1.36.0 · Source

    pub struct Box<T: ?Sized, A: Allocator = Global>(/* private fields */);

Expand description

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

See the module-level documentation for more.

## Implementations§

Source§

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

1.0.0 · Source

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

Attempts 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));

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);
    }

##### §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>

1.0.0 · Source

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

Attempts 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));

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);
    }

##### §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>

Attempts 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));

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);
    }

##### §Safety

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

Source§

### impl<T> Box<T>

1.0.0 · 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);

1.82.0 · Source

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

Constructs a new box with uninitialized contents.

##### §Examples

    let mut five = Box::<u32>::new_uninit();
    // Deferred initialization:
    five.write(5);
    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5)

Source

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

🔬This is a nightly-only experimental API. (`new_zeroed_alloc` #129396)

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_zeroed_alloc)]

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

    assert_eq!(*zero, 0)

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)?;

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)]

    let mut five = Box::<u32>::try_new_uninit()?;
    // Deferred initialization:
    five.write(5);
    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5);

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)]

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

    assert_eq!(*zero, 0);

Source§

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

Source

#### pub fn new_in(x: T, alloc: A) -> Self
where 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);

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)?;

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)]

    use std::alloc::System;

    let mut five = Box::<u32, _>::new_uninit_in(System);
    // Deferred initialization:
    five.write(5);
    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5)

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)]

    use std::alloc::System;

    let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
    // Deferred initialization:
    five.write(5);
    let five = unsafe { five.assume_init() };

    assert_eq!(*five, 5);

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)]

    use std::alloc::System;

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

    assert_eq!(*zero, 0)

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)]

    use std::alloc::System;

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

    assert_eq!(*zero, 0);

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`.

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);

Source§

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

1.82.0 · Source

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

Constructs a new boxed slice with uninitialized contents.

##### §Examples

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

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

Source

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

🔬This is a nightly-only experimental API. (`new_zeroed_alloc` #129396)

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_zeroed_alloc)]

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

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

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)]

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

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

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)]

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

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

Source

#### pub fn into_array<const N: usize>(self) -> Option<Box<[T; N]>>

🔬This is a nightly-only experimental API. (`slice_as_array` #133508)

Converts the boxed slice into a boxed array.

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

If `N` is not exactly equal to the length of `self`, then this method returns `None`.

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)]

    use std::alloc::System;

    let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
    // Deferred initialization:
    values[0].write(1);
    values[1].write(2);
    values[2].write(3);
    let values = unsafe { values.assume_init() };

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

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)]

    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])

Source

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

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

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

##### §Examples

    #![feature(allocator_api)]

    use std::alloc::System;

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

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

Source

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

🔬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. Returns an error if the allocation fails.

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

##### §Examples

    #![feature(allocator_api)]

    use std::alloc::System;

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

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

Source§

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

1.82.0 · Source

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

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

    let mut five = Box::<u32>::new_uninit();
    // Deferred initialization:
    five.write(5);
    let five: Box<u32> = unsafe { five.assume_init() };

    assert_eq!(*five, 5)

1.87.0 · Source

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

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

    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);
    }

Source§

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

1.82.0 · Source

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

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

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

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

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 raw pointer must point to a block of memory allocated by the global allocator.

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) };

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);
    }

Source

#### pub unsafe fn from_non_null(ptr: NonNull<T>) -> Self

🔬This is a nightly-only experimental API. (`box_vec_non_null` #130364)

Constructs a box from a `NonNull` pointer.

After calling this function, the `NonNull` 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 `NonNull` pointer.

The non-null pointer must point to a block of memory allocated by the global allocator.

The safety conditions are described in the memory layout section.

##### §Examples

Recreate a `Box` which was previously converted to a `NonNull` pointer using `Box::into_non_null`:

    #![feature(box_vec_non_null)]

    let x = Box::new(5);
    let non_null = Box::into_non_null(x);
    let x = unsafe { Box::from_non_null(non_null) };

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

    #![feature(box_vec_non_null)]

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

    unsafe {
        let non_null = NonNull::new(alloc(Layout::new::<i32>()).cast::<i32>())
            .expect("allocation failed");
        // In general .write is required to avoid attempting to destruct
        // the (uninitialized) previous contents of `non_null`.
        non_null.write(5);
        let x = Box::from_non_null(non_null);
    }

Source§

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

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.

The raw pointer must point to a block of memory allocated by `alloc`.

##### §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) };

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);
    }

Source

#### pub unsafe fn from_non_null_in(raw: NonNull<T>, alloc: A) -> Self

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

Constructs a box from a `NonNull` pointer in the given allocator.

After calling this function, the `NonNull` 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 non-null pointer must point to a block of memory allocated by `alloc`.

##### §Examples

Recreate a `Box` which was previously converted to a `NonNull` pointer using `Box::into_non_null_with_allocator`:

    #![feature(allocator_api, box_vec_non_null)]

    use std::alloc::System;

    let x = Box::new_in(5, System);
    let (non_null, alloc) = Box::into_non_null_with_allocator(x);
    let x = unsafe { Box::from_non_null_in(non_null, alloc) };

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

    #![feature(allocator_api, box_vec_non_null, slice_ptr_get)]

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

    unsafe {
        let non_null = System.allocate(Layout::new::<i32>())?.cast::<i32>();
        // In general .write is required to avoid attempting to destruct
        // the (uninitialized) previous contents of `non_null`.
        non_null.write(5);
        let x = Box::from_non_null_in(non_null, System);
    }

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) };

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

Note: This is equivalent to the following:

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

Source

#### pub fn into_non_null(b: Self) -> NonNull<T>

🔬This is a nightly-only experimental API. (`box_vec_non_null` #130364)

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

The pointer will be properly aligned.

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 `NonNull` pointer back into a `Box` with the `Box::from_non_null` 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_non_null(b)` instead of `b.into_non_null()`. This is so that there is no conflict with a method on the inner type.

##### §Examples

Converting the `NonNull` pointer back into a `Box` with `Box::from_non_null` for automatic cleanup:

    #![feature(box_vec_non_null)]

    let x = Box::new(String::from("Hello"));
    let non_null = Box::into_non_null(x);
    let x = unsafe { Box::from_non_null(non_null) };

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

    #![feature(box_vec_non_null)]

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

    let x = Box::new(String::from("Hello"));
    let non_null = Box::into_non_null(x);
    unsafe {
        non_null.drop_in_place();
        dealloc(non_null.as_ptr().cast::<u8>(), Layout::new::<String>());
    }

Note: This is equivalent to the following:

    #![feature(box_vec_non_null)]

    let x = Box::new(String::from("Hello"));
    let non_null = Box::into_non_null(x);
    unsafe {
        drop(Box::from_non_null(non_null));
    }

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) };

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>());
    }

Source

#### pub fn into_non_null_with_allocator(b: Self) -> (NonNull<T>, A)

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

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

The pointer will be properly aligned.

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 `NonNull` pointer back into a `Box` with the `Box::from_non_null_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_non_null_with_allocator(b)` instead of `b.into_non_null_with_allocator()`. This is so that there is no conflict with a method on the inner type.

##### §Examples

Converting the `NonNull` pointer back into a `Box` with `Box::from_non_null_in` for automatic cleanup:

    #![feature(allocator_api, box_vec_non_null)]

    use std::alloc::System;

    let x = Box::new_in(String::from("Hello"), System);
    let (non_null, alloc) = Box::into_non_null_with_allocator(x);
    let x = unsafe { Box::from_non_null_in(non_null, alloc) };

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

    #![feature(allocator_api, box_vec_non_null)]

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

    let x = Box::new_in(String::from("Hello"), System);
    let (non_null, alloc) = Box::into_non_null_with_allocator(x);
    unsafe {
        non_null.drop_in_place();
        alloc.deallocate(non_null.cast::<u8>(), Layout::new::<String>());
    }

Source

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

🔬This is a nightly-only experimental API. (`box_as_ptr` #129090)

Returns a raw mutable pointer to the `Box`’s contents.

The caller must ensure that the `Box` outlives the pointer this function returns, or else it will end up dangling.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying memory, and thus the returned pointer will remain valid when mixed with other calls to `as_ptr` and `as_mut_ptr`. Note that calling other methods that materialize references to the memory may still invalidate this pointer. See the example below for how this guarantee can be used.

##### §Examples

Due to the aliasing guarantee, the following code is legal:

    #![feature(box_as_ptr)]

    unsafe {
        let mut b = Box::new(0);
        let ptr1 = Box::as_mut_ptr(&mut b);
        ptr1.write(1);
        let ptr2 = Box::as_mut_ptr(&mut b);
        ptr2.write(2);
        // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
        ptr1.write(3);
    }

Source

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

🔬This is a nightly-only experimental API. (`box_as_ptr` #129090)

Returns a raw pointer to the `Box`’s contents.

The caller must ensure that the `Box` outlives the pointer this function returns, or else it will end up dangling.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an `UnsafeCell`) using this pointer or any pointer derived from it. If you need to mutate the contents of the `Box`, use `as_mut_ptr`.

This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying memory, and thus the returned pointer will remain valid when mixed with other calls to `as_ptr` and `as_mut_ptr`. Note that calling other methods that materialize mutable references to the memory, as well as writing to this memory, may still invalidate this pointer. See the example below for how this guarantee can be used.

##### §Examples

Due to the aliasing guarantee, the following code is legal:

    #![feature(box_as_ptr)]

    unsafe {
        let mut v = Box::new(0);
        let ptr1 = Box::as_ptr(&v);
        let ptr2 = Box::as_mut_ptr(&mut v);
        let _val = ptr2.read();
        // No write to this memory has happened yet, so `ptr1` is still valid.
        let _val = ptr1.read();
        // However, once we do a write...
        ptr2.write(1);
        // ... `ptr1` is no longer valid.
        // This would be UB: let _val = ptr1.read();
    }

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 · 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);

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]);

1.63.0 · 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);

## 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.
1.85.0 · Source§

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

Source§

#### extern "rust-call" fn async_call( &self, args: Args, ) -> Self::CallRefFuture<'_>

🔬This is a nightly-only experimental API. (`async_fn_traits`)
Call the `AsyncFn`, returning a future which may borrow from the called closure.
1.85.0 · Source§

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

Source§

#### type CallRefFuture<'a> = <F as AsyncFnMut<Args>>::CallRefFuture<'a> where Self: 'a

🔬This is a nightly-only experimental API. (`async_fn_traits`)
Future returned by `AsyncFnMut::async_call_mut` and `AsyncFn::async_call`.
Source§

#### extern "rust-call" fn async_call_mut( &mut self, args: Args, ) -> Self::CallRefFuture<'_>

🔬This is a nightly-only experimental API. (`async_fn_traits`)
Call the `AsyncFnMut`, returning a future which may borrow from the called closure.
1.85.0 · Source§

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

Source§

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

🔬This is a nightly-only experimental API. (`async_fn_traits`)
Output type of the called closure’s future.
Source§

#### type CallOnceFuture = <F as AsyncFnOnce<Args>>::CallOnceFuture

🔬This is a nightly-only experimental API. (`async_fn_traits`)
Future returned by `AsyncFnOnce::async_call_once`.
Source§

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

🔬This is a nightly-only experimental API. (`async_fn_traits`)
Call the `AsyncFnOnce`, returning a future which may move out of the called closure.
Source§

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

Source§

#### 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)
Attempts 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_from(&mut self, source: &Self)

Copies `source`’s contents into `self` without creating a new allocation, so long as the two are of the same length.

##### §Examples

    let x = Box::new([5, 6, 7]);
    let mut y = Box::new([8, 9, 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);

Source§

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

Returns a duplicate of the value. Read more
Source§

### impl Clone for Box<ByteStr>

Source§

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

Returns a duplicate of the value. Read more
1.0.0 · Source§

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

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

### impl Clone for Box<CStr>

Source§

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

Returns a duplicate of the value. Read more
1.0.0 · Source§

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

Performs copy-assignment from `source`. Read more
1.0.0 · 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);

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);

1.3.0 · Source§

### impl Clone for Box<str>

Source§

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

Returns a duplicate of the value. Read more
1.0.0 · Source§

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

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

### impl<G: ?Sized + Coroutine<R> + Unpin, R, A: Allocator> Coroutine<R> for Box<G, A>

Source§

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

🔬This is a nightly-only experimental API. (`coroutine_trait` #43122)
The type of value this coroutine yields. Read more
Source§

#### type Return = <G as Coroutine<R>>::Return

🔬This is a nightly-only experimental API. (`coroutine_trait` #43122)
The type of value this coroutine returns. Read more
Source§

#### fn resume( self: Pin<&mut Self>, arg: R, ) -> CoroutineState<Self::Yield, Self::Return>

🔬This is a nightly-only experimental API. (`coroutine_trait` #43122)
Resumes the execution of this coroutine. Read more
Source§

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

Source§

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

🔬This is a nightly-only experimental API. (`coroutine_trait` #43122)
The type of value this coroutine yields. Read more
Source§

#### type Return = <G as Coroutine<R>>::Return

🔬This is a nightly-only experimental API. (`coroutine_trait` #43122)
The type of value this coroutine returns. Read more
Source§

#### fn resume( self: Pin<&mut Self>, arg: R, ) -> CoroutineState<Self::Yield, Self::Return>

🔬This is a nightly-only experimental API. (`coroutine_trait` #43122)
Resumes the execution of this coroutine. Read more
1.0.0 · 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
1.0.0 · Source§

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

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
1.0.0 · 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 · Source§

### impl Default for Box<str>

Source§

#### fn default() -> Self

Returns the “default value” for a type. Read more
1.0.0 · Source§

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

Source§

#### type Target = T

The resulting type after dereferencing.
Source§

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

Dereferences the value.
1.0.0 · Source§

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

Source§

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

Mutably dereferences the value.
1.0.0 · 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
1.0.0 · 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<(), NonZero<usize>>

🔬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) -> R
where 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) -> B
where 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
1.0.0 · 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<E: Error> Error for Box<E>

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)>

Returns the lower-level source of this error, if any. Read more
Source§

#### fn provide<'b>(&'b self, request: &mut Request<'b>)

🔬This is a nightly-only experimental API. (`error_generic_member_access` #99301)
Provides type-based access to context intended for error reports. Read more
1.0.0 · 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<A: Allocator> Extend<Box<str, A>> for String

Source§

#### fn extend<I: IntoIterator<Item = Box<str, A>>>(&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>

Source§

#### 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: Clone> 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:?}");

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`.

1.84.0 · Source§

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

Source§

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

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

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

##### §Examples

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

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

1.84.0 · Source§

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

Source§

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

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

1.84.0 · Source§

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

Source§

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

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

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

##### §Examples

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

1.6.0 · Source§

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

Source§

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

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

##### §Examples

    use std::error::Error;

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

1.0.0 · 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;

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

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}");

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:?}");

1.18.0 · Source§

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

Source§

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

Converts 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]);

Source§

### impl From<Box<[u8]>> for Box<ByteStr>

Source§

#### fn from(s: Box<[u8]>) -> Box<ByteStr>

Converts to this type from the input type.
Source§

### impl From<Box<ByteStr>> for Box<[u8]>

Source§

#### fn from(s: Box<ByteStr>) -> Box<[u8]>

Converts to this type from the input type.
1.18.0 · Source§

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

Source§

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

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

1.21.0 · Source§

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

Source§

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

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[..]);

1.33.0 · Source§

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

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, A: Allocator> From<Box<T, A>> for Rc<T, A>

Source§

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

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);

1.18.0 · Source§

### impl From<Box<str>> 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

    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)

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);

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: Clone> 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}");

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

1.22.0 · Source§

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

Source§

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

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

##### §Examples

    use std::error::Error;
    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!(size_of::<Box<dyn Error>>() == size_of_val(&a_boxed_error))

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::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!(
        size_of::<Box<dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

1.0.0 · 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;

    #[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 == size_of_val(&an_error));
    let a_boxed_error = Box::<dyn Error>::from(an_error);
    assert!(size_of::<Box<dyn Error>>() == size_of_val(&a_boxed_error))

1.0.0 · 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;

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

1.6.0 · Source§

### impl<'a> From<String> for Box<dyn Error + 'a>

Source§

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

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

##### §Examples

    use std::error::Error;

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

1.0.0 · Source§

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

Source§

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

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

##### §Examples

    use std::error::Error;

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

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

    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)

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);

1.20.0 · Source§

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

Source§

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

Converts a vector into a boxed slice.

Before doing the conversion, this method discards excess capacity like `Vec::shrink_to_fit`.

##### §Examples

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

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());

1.80.0 · Source§

### impl<'a> FromIterator<&'a char> for Box<str>

Source§

#### fn from_iter<T: IntoIterator<Item = &'a char>>(iter: T) -> Self

Creates a value from an iterator. Read more
1.80.0 · Source§

### impl<'a> FromIterator<&'a str> for Box<str>

Source§

#### fn from_iter<T: IntoIterator<Item = &'a str>>(iter: T) -> Self

Creates a value from an iterator. Read more
1.80.0 · Source§

### impl<A: Allocator> FromIterator<Box<str, A>> for Box<str>

Source§

#### fn from_iter<T: IntoIterator<Item = Box<str, A>>>(iter: T) -> Self

Creates a value from an iterator. Read more
1.45.0 · Source§

### impl<A: Allocator> FromIterator<Box<str, A>> for String

Source§

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

Creates a value from an iterator. Read more
1.80.0 · Source§

### impl<'a> FromIterator<Cow<'a, str>> for Box<str>

Source§

#### fn from_iter<T: IntoIterator<Item = Cow<'a, str>>>(iter: T) -> Self

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
1.80.0 · Source§

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

Source§

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

Creates a value from an iterator. Read more
1.80.0 · Source§

### impl FromIterator<char> for Box<str>

Source§

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

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

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

Source§

#### 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>

Attempts to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more
1.0.0 · Source§

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

Source§

#### 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>

Source§

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

Returns the hash value for the values written so far. Read more
Source§

#### fn write(&mut self, bytes: &[u8])

Writes some data into this `Hasher`. Read more
Source§

#### fn write_u8(&mut self, i: u8)

Writes a single `u8` into this hasher.
Source§

#### fn write_u16(&mut self, i: u16)

Writes a single `u16` into this hasher.
Source§

#### fn write_u32(&mut self, i: u32)

Writes a single `u32` into this hasher.
Source§

#### fn write_u64(&mut self, i: u64)

Writes a single `u64` into this hasher.
Source§

#### fn write_u128(&mut self, i: u128)

Writes a single `u128` into this hasher.
Source§

#### fn write_usize(&mut self, i: usize)

Writes a single `usize` into this hasher.
Source§

#### fn write_i8(&mut self, i: i8)

Writes a single `i8` into this hasher.
Source§

#### fn write_i16(&mut self, i: i16)

Writes a single `i16` into this hasher.
Source§

#### fn write_i32(&mut self, i: i32)

Writes a single `i32` into this hasher.
Source§

#### fn write_i64(&mut self, i: i64)

Writes a single `i64` into this hasher.
Source§

#### fn write_i128(&mut self, i: i128)

Writes a single `i128` into this hasher.
Source§

#### fn write_isize(&mut self, i: isize)

Writes a single `isize` into this hasher.
Source§

#### 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
Source§

#### 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
1.80.0 · Source§

### impl<'a, I, A: Allocator> IntoIterator for &'a Box<[I], A>

Source§

#### type IntoIter = Iter<'a, I>

Which kind of iterator are we turning this into?
Source§

#### type Item = &'a I

The type of the elements being iterated over.
Source§

#### fn into_iter(self) -> Iter<'a, I> ⓘ

Creates an iterator from a value. Read more
1.80.0 · Source§

### impl<'a, I, A: Allocator> IntoIterator for &'a mut Box<[I], A>

Source§

#### type IntoIter = IterMut<'a, I>

Which kind of iterator are we turning this into?
Source§

#### type Item = &'a mut I

The type of the elements being iterated over.
Source§

#### fn into_iter(self) -> IterMut<'a, I> ⓘ

Creates an iterator from a value. Read more
1.80.0 · Source§

### impl<I, A: Allocator> IntoIterator for Box<[I], A>

Source§

#### type IntoIter = IntoIter<I, A>

Which kind of iterator are we turning this into?
Source§

#### type Item = I

The type of the elements being iterated over.
Source§

#### fn into_iter(self) -> IntoIter<I, A> ⓘ

Creates an iterator from a value. Read more
1.0.0 · Source§

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

Source§

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

The type of the elements being iterated over.
Source§

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

Advances the iterator and returns the next value. Read more
Source§

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

Returns the bounds on the remaining length of the iterator. Read more
Source§

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

Returns the `n`th element of the iterator. Read more
Source§

#### fn last(self) -> Option<I::Item>

Consumes the iterator, returning the last element. Read more
Source§

#### 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
1.0.0 · Source§

#### fn count(self) -> usize
where Self: Sized,

Consumes the iterator, counting the number of iterations and returning it. Read more
Source§

#### fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>

🔬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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
Source§

#### fn intersperse(self, separator: Self::Item) -> Intersperse<Self>
where Self: Sized, Self::Item: Clone,

🔬This is a nightly-only experimental API. (`iter_intersperse` #79524)
Creates a new iterator which places a copy of `separator` between adjacent items of the original iterator. Read more
Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### fn skip(self, n: usize) -> Skip<Self>
where Self: Sized,

Creates an iterator that skips the first `n` elements. Read more
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.29.0 · Source§

#### fn flatten(self) -> Flatten<Self>
where Self: Sized, Self::Item: IntoIterator,

Creates an iterator that flattens nested structure. Read more
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#### fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N>
where Self: Sized, F: FnMut(&[Self::Item; N]) -> R,

🔬This is a nightly-only experimental API. (`iter_map_windows` #87155)
Calls the given function `f` for each contiguous window of size `N` over `self` and returns an iterator over the outputs of `f`. Like `slice::windows()`, the windows during mapping overlap as well. Read more
1.0.0 · Source§

#### fn fuse(self) -> Fuse<Self>
where Self: Sized,

Creates an iterator which ends after the first `None`. Read more
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### fn by_ref(&mut self) -> &mut Self
where Self: Sized,

Creates a “by reference” adapter for this instance of `Iterator`. Read more
1.0.0 · Source§

#### fn collect<B>(self) -> B
where B: FromIterator<Self::Item>, Self: Sized,

Transforms an iterator into a collection. Read more
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#### fn try_collect<B>( &mut self, ) -> <<Self::Item as Try>::Residual as Residual<B>>::TryType
where Self: Sized, Self::Item: Try, <Self::Item as Try>::Residual: Residual<B>, B: FromIterator<<Self::Item as Try>::Output>,

🔬This is a nightly-only experimental API. (`iterator_try_collect` #94047)
Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered. 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
1.0.0 · Source§

#### 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 partition_in_place<'a, T, P>(self, predicate: P) -> usize
where T: 'a, Self: Sized + DoubleEndedIterator<Item = &'a mut T>, P: FnMut(&T) -> bool,

🔬This is a nightly-only experimental API. (`iter_partition_in_place` #62543)
Reorders the elements of this iterator in-place according to the given predicate, such that all those that return `true` precede all those that return `false`. Returns the number of `true` elements found. 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) -> R
where 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) -> R
where 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
1.0.0 · Source§

#### fn fold<B, F>(self, init: B, f: F) -> B
where 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<R>( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
where Self: Sized, 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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<R>( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
where Self: Sized, 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### fn rposition<P>(&mut self, predicate: P) -> Option<usize>
where P: FnMut(Self::Item) -> bool, Self: Sized + ExactSizeIterator + DoubleEndedIterator,

Searches for an element in an iterator from the right, returning its index. Read more
1.0.0 · Source§

#### fn max(self) -> Option<Self::Item>
where Self: Sized, Self::Item: Ord,

Returns the maximum element of an iterator. Read more
1.0.0 · Source§

#### fn min(self) -> Option<Self::Item>
where Self: Sized, Self::Item: Ord,

Returns the minimum element of an iterator. 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
1.0.0 · Source§

#### fn rev(self) -> Rev<Self>
where Self: Sized + DoubleEndedIterator,

Reverses an iterator’s direction. Read more
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### 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
1.0.0 · Source§

#### fn cycle(self) -> Cycle<Self>
where Self: Sized + Clone,

Repeats an iterator endlessly. 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) -> S
where Self: Sized, S: Sum<Self::Item>,

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

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

Iterates over the entire iterator, multiplying all the elements Read more
1.5.0 · Source§

#### fn cmp<I>(self, other: I) -> Ordering
where I: IntoIterator<Item = Self::Item>, Self::Item: Ord, Self: Sized,

Lexicographically compares the elements of this `Iterator` with those of another. 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
1.82.0 · Source§

#### fn is_sorted(self) -> bool
where Self: Sized, Self::Item: PartialOrd,

Checks if the elements of this iterator are sorted. Read more
1.82.0 · Source§

#### fn is_sorted_by<F>(self, compare: F) -> bool
where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> bool,

Checks if the elements of this iterator are sorted using the given comparator function. Read more
1.82.0 · Source§

#### fn is_sorted_by_key<F, K>(self, f: F) -> bool
where Self: Sized, F: FnMut(Self::Item) -> K, K: PartialOrd,

Checks if the elements of this iterator are sorted using the given key extraction function. Read more
1.0.0 · Source§

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

Source§

#### 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) -> Self
where Self: Sized,

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

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

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

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

Restrict a value to a certain interval. Read more
1.0.0 · Source§

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

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

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

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

Source§

#### 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

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

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

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

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 · Source§

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

Source§

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

Formats the value using the given formatter. Read more
1.43.0 · Source§

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

Source§

#### 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]>

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

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

Source§

#### 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);

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#### type Error = Vec<T>

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, A: Allocator> DerefPure for Box<T, A>

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

1.0.0 · Source§

### 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>

1.80.0 · Source§

### impl<'a, I, A: Allocator> !Iterator for &'a Box<[I], A>

This implementation is required to make sure that the `&Box<[I]>: IntoIterator` implementation doesn’t overlap with `IntoIterator for T where T: Iterator` blanket.

1.80.0 · Source§

### impl<'a, I, A: Allocator> !Iterator for &'a mut Box<[I], A>

This implementation is required to make sure that the `&mut Box<[I]>: IntoIterator` implementation doesn’t overlap with `IntoIterator for T where T: Iterator` blanket.

1.80.0 · Source§

### impl<I, A: Allocator> !Iterator for Box<[I], A>

This implementation is required to make sure that the `Box<[I]>: IntoIterator` implementation doesn’t overlap with `IntoIterator for T where T: Iterator` blanket.

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

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### impl<T> PointerLike for Box<T>

1.33.0 · Source§

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

## Auto Trait Implementations§

§

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

§

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

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

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

§

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

## Blanket Implementations§

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

Source§

#### 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> CloneToUninit for T
where T: Clone,

Source§

#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<!> for T

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

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

Source§

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

Returns the argument unchanged.

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

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<I> IntoAsyncIterator for I
where I: AsyncIterator,

Source§

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

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
The type of the item yielded by the iterator
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#### type IntoAsyncIter = I

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
The type of the resulting iterator
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#### fn into_async_iter(self) -> <I as IntoAsyncIterator>::IntoAsyncIter

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
Converts `self` into an async iterator
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### impl<F> IntoFuture for F
where F: Future,

Source§

#### 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 I
where I: Iterator,

Source§

#### 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?
Source§

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

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

Source§

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

🔬This is a nightly-only experimental API. (`pattern` #27721)
Associated searcher for this pattern
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#### fn into_searcher<'a>(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<'a>(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<'a>(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
Source§

#### fn strip_prefix_of<'a>(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.
Source§

#### fn is_suffix_of<'a>(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<'a>(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.
Source§

#### fn as_utf8_pattern(&self) -> Option<Utf8Pattern<'_>>

🔬This is a nightly-only experimental API. (`pattern` #27721)
Returns the pattern as utf-8 bytes if possible.
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### impl<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,

Source§

#### type Target = T

🔬This is a nightly-only experimental API. (`arbitrary_self_types` #44874)
The target type on which the method may be called.
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### impl<T> ToOwned for T
where 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 T
where T: Display + ?Sized,

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

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

Source§

#### 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.