Struct Box

pub struct BoxGlobal>(/* private fields */)
where
    A: Allocator,
    T: ?Sized;

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

See the module-level documentation for more.

Implementations

impl BoxAny, A>

where A: Allocator,

pub fn downcast(self) -> Result<Box, BoxAny, A>>

where T: Any,

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::() {
        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));

pub unsafe fn downcast_unchecked(self) -> Box

where T: Any,

🔬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::(), 1);
}

Safety

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

impl BoxAny + Send, A>

where A: Allocator,

pub fn downcast(self) -> Result<Box, BoxAny + Send, A>>

where T: Any,

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::() {
        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));

pub unsafe fn downcast_unchecked(self) -> Box

where T: Any,

🔬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::(), 1);
}

Safety

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

impl BoxAny + Sync + Send, A>

where A: Allocator,

pub fn downcast(self) -> Result<Box, BoxAny + Sync + Send, A>>

where T: Any,

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::() {
        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));

pub unsafe fn downcast_unchecked(self) -> Box

where T: Any,

🔬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::(), 1);
}

Safety

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

impl Box

pub fn new(x: T) -> Box

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);

pub fn new_uninit() -> Box<MaybeUninit>

Constructs a new box with uninitialized contents.

Examples

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

assert_eq!(*five, 5)

pub fn new_zeroed() -> Box<MaybeUninit>

🔬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::::new_zeroed();
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0)

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

Constructs a new Pin>. 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, or if you want to construct a (pinned) Box in a different way than with Box::new.

pub fn try_new(x: T) -> Result<Box, 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)?;

pub fn try_new_uninit() -> Result<Box<MaybeUninit>, 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::::try_new_uninit()?;
// Deferred initialization:
five.write(5);
let five = unsafe { five.assume_init() };

assert_eq!(*five, 5);

pub fn try_new_zeroed() -> Result<Box<MaybeUninit>, 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::::try_new_zeroed()?;
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0);

impl Box

where A: Allocator,

pub fn new_in(x: T, alloc: A) -> Box

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);

pub fn try_new_in(x: T, alloc: A) -> Result<Box, 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)?;

pub fn new_uninit_in(alloc: A) -> Box<MaybeUninit, 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::_>::new_uninit_in(System);
// Deferred initialization:
five.write(5);
let five = unsafe { five.assume_init() };

assert_eq!(*five, 5)

pub fn try_new_uninit_in(alloc: A) -> Result<Box<MaybeUninit, 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::_>::try_new_uninit_in(System)?;
// Deferred initialization:
five.write(5);
let five = unsafe { five.assume_init() };

assert_eq!(*five, 5);

pub fn new_zeroed_in(alloc: A) -> Box<MaybeUninit, 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::_>::new_zeroed_in(System);
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0)

pub fn try_new_zeroed_in(alloc: A) -> Result<Box<MaybeUninit, 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::_>::try_new_zeroed_in(System)?;
let zero = unsafe { zero.assume_init() };

assert_eq!(*zero, 0);

pub fn pin_in(x: T, alloc: A) -> Pin<Box>

where A: 'static + Allocator,

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

Constructs a new Pin>. 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, or if you want to construct a (pinned) Box in a different way than with Box::new_in.

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

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

Converts a Box into a Box<[T]>

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

pub fn into_inner(boxed: Box) -> 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);

impl Box<[T]>

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

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])

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

🔬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])

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

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

pub fn into_arrayusize>(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.

impl Box<[T], A>

where A: Allocator,

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

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

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

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

impl Box<MaybeUninit, A>

where A: Allocator,

pub unsafe fn assume_init(self) -> Box

Converts to Box.

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

assert_eq!(*five, 5)

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

Writes the value and converts to Box.

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);
}

impl Box<[MaybeUninit], A>

where A: Allocator,

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])

impl Box

where T: ?Sized,

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

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::()) 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);
}

pub unsafe fn from_non_null(ptr: NonNull) -> Box

🔬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::()).cast::())
        .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);
}

impl Box

where A: Allocator, T: ?Sized,

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

🔬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::())?.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);
}

pub unsafe fn from_non_null_in(raw: NonNull, alloc: A) -> Box

🔬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::())?.cast::();
    // 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);
}

pub fn into_raw(b: Box) -> *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::());
}

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));
}

pub fn into_non_null(b: Box) -> NonNull

🔬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::(), Layout::new::());
}

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));
}

pub fn into_raw_with_allocator(b: Box) -> (*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::());
}

pub fn into_non_null_with_allocator(b: Box) -> (NonNull, 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::(), Layout::new::());
}

pub fn as_mut_ptr(b: &mut Box) -> *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);
}

pub fn as_ptr(b: &Box) -> *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();
}

pub fn allocator(b: &Box) -> &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.

pub fn leak<'a>(b: Box) -> &'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]);

pub fn into_pin(boxed: Box) -> Pin<Box>

where A: 'static,

Converts a Box into a Pin>. 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, 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> for Pin, 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> for Pin {
    fn from(_: Box<()>) -> Pin {
        Pin::new(Foo)
    }
}

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

Trait Implementations

implAsFd + ?Sized> AsFd for Box

fn as_fd(&self) -> BorrowedFd<'_>

Borrows the file descriptor.

implAsHandle + ?Sized> AsHandle for Box

Available on Windows only.

fn as_handle(&self) -> BorrowedHandle<'_>

Borrows the handle.

impl AsMut for Box

where A: Allocator, T: ?Sized,

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

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

implAsRawFd> AsRawFd for Box

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl AsRef for Box

where A: Allocator, T: ?Sized,

fn as_ref(&self) -> &T

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

implAsSocket> AsSocket for Box

Available on Windows only.

fn as_socket(&self) -> BorrowedSocket<'_>

Borrows the socket.

impl AsyncFn for Box

where Args: Tuple, F: AsyncFn + ?Sized, A: Allocator,

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

🔬This is a nightly-only experimental API. (async_fn_traits)

Call the AsyncFn, returning a future which may borrow from the called closure.

impl AsyncFnMut for Box

where Args: Tuple, F: AsyncFnMut + ?Sized, A: Allocator,

type CallRefFuture<'a> = AsyncFnMut>::CallRefFuture<'a> where Box: 'a

🔬This is a nightly-only experimental API. (async_fn_traits)

Future returned by AsyncFnMut::async_call_mut and AsyncFn::async_call.

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

🔬This is a nightly-only experimental API. (async_fn_traits)

Call the AsyncFnMut, returning a future which may borrow from the called closure.

impl AsyncFnOnce for Box

where Args: Tuple, F: AsyncFnOnce + ?Sized, A: Allocator,

type Output = AsyncFnOnce>::Output

🔬This is a nightly-only experimental API. (async_fn_traits)

Output type of the called closure’s future.

type CallOnceFuture = AsyncFnOnce>::CallOnceFuture

🔬This is a nightly-only experimental API. (async_fn_traits)

Future returned by AsyncFnOnce::async_call_once.

extern "rust-call" fn async_call_once( self, args: Args, ) -> <Box as AsyncFnOnce>::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.

impl AsyncIterator for Box

where S: AsyncIterator + Unpin + ?Sized,

type Item = AsyncIterator>::Item

🔬This is a nightly-only experimental API. (async_iterator #79024)

The type of items yielded by the async iterator.

fn poll_next( self: Pin<&mut Box>, cx: &mut Context<'_>, ) -> Poll<Option<<Box as AsyncIterator>::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.

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.

impl Borrow for Box

where A: Allocator, T: ?Sized,

fn borrow(&self) -> &T

Immutably borrows from an owned value.

impl BorrowMut for Box

where A: Allocator, T: ?Sized,

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

Mutably borrows from an owned value.

implBufRead + ?Sized> BufRead for Box

fn fill_buf(&mut self) -> Result<&[u8]>

Returns the contents of the internal buffer, filling it with more data, via Read methods, if empty.

fn consume(&mut self, amt: usize)

Marks the given amount of additional bytes from the internal buffer as having been read. Subsequent calls to read only return bytes that have not been marked as read.

fn has_data_left(&mut self) -> Result<bool>

🔬This is a nightly-only experimental API. (buf_read_has_data_left #86423)

Checks if there is any data left to be read.

fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> Result<usize>

Reads all bytes into buf until the delimiter byte or EOF is reached.

fn skip_until(&mut self, byte: u8) -> Result<usize>

Skips all bytes until the delimiter byte or EOF is reached.

fn read_line(&mut self, buf: &mut String) -> Result<usize>

Reads all bytes until a newline (the 0xA byte) is reached, and append them to the provided String buffer.

fn split(self, byte: u8) -> Split

where Self: Sized,

Returns an iterator over the contents of this reader split on the byte byte.

fn lines(self) -> Lines

where Self: Sized,

Returns an iterator over the lines of this reader.

impl Clone for Box<[T], A>

where T: Clone, A: Allocator + Clone,

fn clone_from(&mut self, source: &Box<[T], A>)

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);

fn clone(&self) -> Box<[T], A>

Returns a copy of the value.

impl Clone for Box<ByteStr>

fn clone(&self) -> Box<ByteStr>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Clone for Box<CStr>

fn clone(&self) -> Box<CStr>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Clone for Box<OsStr>

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Clone for Box<Path>

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Clone for Box

where T: Clone, A: Allocator + Clone,

fn clone(&self) -> Box

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);

fn clone_from(&mut self, source: &Box)

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);

impl Clone for Box<str>

fn clone(&self) -> Box<str>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Coroutine for Box

where G: Coroutine + Unpin + ?Sized, A: Allocator,

type Yield = Coroutine>::Yield

🔬This is a nightly-only experimental API. (coroutine_trait #43122)

The type of value this coroutine yields.

type Return = Coroutine>::Return

🔬This is a nightly-only experimental API. (coroutine_trait #43122)

The type of value this coroutine returns.

fn resume( self: Pin<&mut Box>, arg: R, ) -> CoroutineState<<Box as Coroutine>::Yield, <Box as Coroutine>::Return>

🔬This is a nightly-only experimental API. (coroutine_trait #43122)

Resumes the execution of this coroutine.

impl Coroutine for Pin<Box>

where G: Coroutine + ?Sized, A: Allocator + 'static,

type Yield = Coroutine>::Yield

🔬This is a nightly-only experimental API. (coroutine_trait #43122)

The type of value this coroutine yields.

type Return = Coroutine>::Return

🔬This is a nightly-only experimental API. (coroutine_trait #43122)

The type of value this coroutine returns.

fn resume( self: Pin<&mut Pin<Box>>, arg: R, ) -> CoroutineState<<Pin<Box> as Coroutine>::Yield, <Pin<Box> as Coroutine>::Return>

🔬This is a nightly-only experimental API. (coroutine_trait #43122)

Resumes the execution of this coroutine.

impl Debug for Box

where T: Debug + ?Sized, A: Allocator,

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

Formats the value using the given formatter.

impl Default for Box<[T]>

fn default() -> Box<[T]>

Returns the “default value” for a type.

impl Default for Box<CStr>

fn default() -> Box<CStr>

Returns the “default value” for a type.

impl Default for Box<OsStr>

fn default() -> Box<OsStr>

Returns the “default value” for a type.

impl Default for Box

where T: Default,

fn default() -> Box

Creates a Box, with the Default value for T.

impl Default for Box<str>

fn default() -> Box<str>

Returns the “default value” for a type.

impl Deref for Box

where A: Allocator, T: ?Sized,

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl DerefMut for Box

where A: Allocator, T: ?Sized,

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

Mutably dereferences the value.

impl Display for Box

where T: Display + ?Sized, A: Allocator,

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

Formats the value using the given formatter.

impl DoubleEndedIterator for Box

where I: DoubleEndedIterator + ?Sized, A: Allocator,

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

Removes and returns an element from the end of the iterator.

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

Returns the nth element from the end of the iterator.

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.

fn try_rfold(&mut self, init: B, f: F) -> R

where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try

,

This is the reverse version of Iterator::try_fold(): it takes elements starting from the back of the iterator.

fn rfold(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.

fn rfind

(&mut self, predicate: P) -> OptionItem>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator from the back that satisfies a predicate.

impl Drop for Box

where A: Allocator, T: ?Sized,

fn drop(&mut self)

Executes the destructor for this type.

impl Error for Box

where E: Error,

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

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

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

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

Returns the lower-level source of this error, if any.

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.

impl ExactSizeIterator for Box

where I: ExactSizeIterator + ?Sized, A: Allocator,

fn len(&self) -> usize

Returns the exact remaining length of the iterator.

fn is_empty(&self) -> bool

🔬This is a nightly-only experimental API. (exact_size_is_empty #35428)

Returns true if the iterator is empty.

impl Extend<Box<str, A>> for String

where A: Allocator,

fn extend(&mut self, iter: I)

where I: IntoIteratorBox<str, A>>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

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.

impl Fn for Box

where Args: Tuple, F: Fn + ?Sized, A: Allocator,

extern "rust-call" fn call( &self, args: Args, ) -> <Box as FnOnce>::Output

🔬This is a nightly-only experimental API. (fn_traits #29625)

Performs the call operation.

impl FnMut for Box

where Args: Tuple, F: FnMut + ?Sized, A: Allocator,

extern "rust-call" fn call_mut( &mut self, args: Args, ) -> <Box as FnOnce>::Output

🔬This is a nightly-only experimental API. (fn_traits #29625)

Performs the call operation.

impl FnOnce for Box

where Args: Tuple, F: FnOnce + ?Sized, A: Allocator,

type Output = FnOnce>::Output

The returned type after the call operator is used.

extern "rust-call" fn call_once( self, args: Args, ) -> <Box as FnOnce>::Output

🔬This is a nightly-only experimental API. (fn_traits #29625)

Performs the call operation.

impl From<&[T]> for Box<[T]>

where T: Clone,

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:?}");

impl From<&CStr> for Box<CStr>

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

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

impl From<&OsStr> for Box<OsStr>

fn from(s: &OsStr) -> Box<OsStr>

Copies the string into a newly allocated Box<OsStr>.

impl From<&Path> for Box<Path>

fn from(path: &Path) -> Box<Path>

Creates a boxed Path from a reference.

This will allocate and clone path to it.

impl From<&mut [T]> for Box<[T]>

where T: Clone,

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:?}");

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

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

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

impl From<&mut OsStr> for Box<OsStr>

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

Copies the string into a newly allocated Box<OsStr>.

impl From<&mut Path> for Box<Path>

fn from(path: &mut Path) -> Box<Path>

Creates a boxed Path from a reference.

This will allocate and clone path to it.

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

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

Converts a &mut str into a Box

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 = Box::from(original);
println!("{boxed}");

impl<'a> From<&str> for BoxError + 'a>

fn from(err: &str) -> BoxError + '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::dyn Error>>() == size_of_val(&a_boxed_error))

impl<'a> From<&str> for BoxError + Sync + Send + 'a>

fn from(err: &str) -> BoxError + Sync + Send + '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::dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

impl From<&str> for Box<str>

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

Converts a &str into a Box

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

Examples

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

implusize> From<[T; N]> for Box<[T]>

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:?}");

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

where A: Allocator,

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

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]);

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

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

Converts to this type from the input type.

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

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

Converts to this type from the input type.

impl From<Box<CStr>> for CString

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

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

impl From<Box<OsStr>> for OsString

fn from(boxed: Box<OsStr>) -> OsString

Converts a Box<OsStr> into an OsString without copying or allocating.

impl From<Box<Path>> for PathBuf

fn from(boxed: Box<Path>) -> PathBuf

Converts a Box<Path> into a PathBuf.

This conversion does not allocate or copy memory.

impl From<Box> for Arc

where A: Allocator, T: ?Sized,

fn from(v: Box) -> Arc

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

Example

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

impl From<Box> for Pin<Box>

where A: Allocator + 'static, T: ?Sized,

fn from(boxed: Box) -> Pin<Box>

Converts a Box into a Pin>. 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 >>::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, or you are constructing a (pinned) Box in a different way than with Box::new.

impl From<Box> for Rc

where A: Allocator, T: ?Sized,

fn from(v: Box) -> Rc

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

Example

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

impl From<Box<str>> for String

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 = s1.into_boxed_str();
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

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

where A: Allocator,

fn from(s: Box<str, A>) -> Box<[u8], A>

Converts a Box into a Box<[u8]>

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

Examples

// create a Box which will be used to create a Box<[u8]>
let boxed: Box = 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);

impl From<CString> for Box<CStr>

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

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

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

where T: Clone,

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.

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

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

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

impl From<Cow<'_, OsStr>> for Box<OsStr>

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

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

impl From<Cow<'_, Path>> for Box<Path>

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

Creates a boxed Path from a clone-on-write pointer.

Converting from a Cow::Owned does not clone or allocate.

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

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

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

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 = Box::from(unboxed);
println!("{boxed}");

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

impl<'a, 'b> From<Cow<'b, str>> for BoxError + 'a>

fn from(err: Cow<'b, str>) -> BoxError + '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::dyn Error>>() == size_of_val(&a_boxed_error))

impl<'a, 'b> From<Cow<'b, str>> for BoxError + Sync + Send + 'a>

fn from(err: Cow<'b, str>) -> BoxError + Sync + Send + '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::dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

impl<'a, E> From for BoxError + 'a>

where E: Error + 'a,

fn from(err: E) -> BoxError + '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::dyn Error>>() == size_of_val(&a_boxed_error))

impl<'a, E> From for BoxError + Sync + Send + 'a>

where E: Error + Send + Sync + 'a,

fn from(err: E) -> BoxError + Sync + Send + '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::dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

impl From<OsString> for Box<OsStr>

fn from(s: OsString) -> Box<OsStr>

Converts an OsString into a Box<OsStr> without copying or allocating.

impl From<PathBuf> for Box<Path>

fn from(p: PathBuf) -> Box<Path>

Converts a PathBuf into a Box<Path>.

This conversion currently should not allocate memory, but this behavior is not guaranteed on all platforms or in all future versions.

impl<'a> From<String> for BoxError + 'a>

fn from(str_err: String) -> BoxError + '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::dyn Error>>() == size_of_val(&a_boxed_error))

impl<'a> From<String> for BoxError + Sync + Send + 'a>

fn from(err: String) -> BoxError + Sync + Send + '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::dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

impl From<String> for Box<str>

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 = Box::from(s1);
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

impl From for Box

fn from(t: T) -> Box

Converts a T into a Box

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);

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

where A: Allocator,

fn from(v: Vec) -> Box<[T], A>

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());

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

fn from_iter(iter: T) -> Box<str>

where T: IntoIteratorchar>,

Creates a value from an iterator.

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

fn from_iter(iter: T) -> Box<str>

where T: IntoIteratorstr>,

Creates a value from an iterator.

impl FromIterator<Box<str, A>> for Box<str>

where A: Allocator,

fn from_iter(iter: T) -> Box<str>

where T: IntoIteratorBox<str, A>>,

Creates a value from an iterator.

impl FromIterator<Box<str, A>> for String

where A: Allocator,

fn from_iter(iter: I) -> String

where I: IntoIteratorBox<str, A>>,

Creates a value from an iterator.

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

fn from_iter(iter: T) -> Box<str>

where T: IntoIteratorCow<'a, str>>,

Creates a value from an iterator.

impl FromIterator for Box<[I]>

fn from_iter(iter: T) -> Box<[I]>

where T: IntoIterator,

Creates a value from an iterator.

impl FromIterator<String> for Box<str>

fn from_iter(iter: T) -> Box<str>

where T: IntoIteratorString>,

Creates a value from an iterator.

impl FromIterator<char> for Box<str>

fn from_iter(iter: T) -> Box<str>

where T: IntoIteratorchar>,

Creates a value from an iterator.

impl Future for Box

where F: Future + Unpin + ?Sized, A: Allocator,

type Output = Future>::Output

The type of value produced on completion.

fn poll( self: Pin<&mut Box>, cx: &mut Context<'_>, ) -> Poll<<Box as Future>::Output>

Attempts to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.

impl Hash for Box

where T: Hash + ?Sized, A: Allocator,

fn hash(&self, state: &mut H)

where H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Hasher for Box

where T: Hasher + ?Sized, A: Allocator,

fn finish(&self) -> u64

Returns the hash value for the values written so far.

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

Writes some data into this Hasher.

fn write_u8(&mut self, i: u8)

Writes a single u8 into this hasher.

fn write_u16(&mut self, i: u16)

Writes a single u16 into this hasher.

fn write_u32(&mut self, i: u32)

Writes a single u32 into this hasher.

fn write_u64(&mut self, i: u64)

Writes a single u64 into this hasher.

fn write_u128(&mut self, i: u128)

Writes a single u128 into this hasher.

fn write_usize(&mut self, i: usize)

Writes a single usize into this hasher.

fn write_i8(&mut self, i: i8)

Writes a single i8 into this hasher.

fn write_i16(&mut self, i: i16)

Writes a single i16 into this hasher.

fn write_i32(&mut self, i: i32)

Writes a single i32 into this hasher.

fn write_i64(&mut self, i: i64)

Writes a single i64 into this hasher.

fn write_i128(&mut self, i: i128)

Writes a single i128 into this hasher.

fn write_isize(&mut self, i: isize)

Writes a single isize into this hasher.

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.

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.

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

where A: Allocator,

type IntoIter = Iter<'a, I>

Which kind of iterator are we turning this into?

type Item = &'a I

The type of the elements being iterated over.

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

Creates an iterator from a value.

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

where A: Allocator,

type IntoIter = IterMut<'a, I>

Which kind of iterator are we turning this into?

type Item = &'a mut I

The type of the elements being iterated over.

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

Creates an iterator from a value.

impl IntoIterator for Box<[I], A>

where A: Allocator,

type IntoIter = IntoIter

Which kind of iterator are we turning this into?

type Item = I

The type of the elements being iterated over.

fn into_iter(self) -> IntoIter

Creates an iterator from a value.

impl Iterator for Box

where I: Iterator + ?Sized, A: Allocator,

type Item = Iterator>::Item

The type of the elements being iterated over.

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

Advances the iterator and returns the next value.

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

Returns the bounds on the remaining length of the iterator.

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

Returns the nth element of the iterator.

fn last(self) -> Option<Iterator>::Item>

Consumes the iterator, returning the last element.

fn next_chunkusize>( &mut self, ) -> Result<[Self::Item; N], IntoIterItem, 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.

fn count(self) -> usize

where Self: Sized,

Consumes the iterator, counting the number of iterations and returning it.

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.

fn step_by(self, step: usize) -> StepBy

where Self: Sized,

Creates an iterator starting at the same point, but stepping by the given amount at each iteration.

fn chain(self, other: U) -> ChainIntoIterator>::IntoIter>

where Self: Sized, U: IntoIteratorItem>,

Takes two iterators and creates a new iterator over both in sequence.

fn zip(self, other: U) -> ZipIntoIterator>::IntoIter>

where Self: Sized, U: IntoIterator,

‘Zips up’ two iterators into a single iterator of pairs.

fn intersperse(self, separator: Self::Item) -> Intersperse

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.

fn intersperse_with(self, separator: G) -> IntersperseWith

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.

fn map(self, f: F) -> Map

where Self: Sized, F: FnMut(Self::Item) -> B,

Takes a closure and creates an iterator which calls that closure on each element.

fn for_each(self, f: F)

where Self: Sized, F: FnMut(Self::Item),

Calls a closure on each element of an iterator.

fn filter

(self, predicate: P) -> Filter

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator which uses a closure to determine if an element should be yielded.

fn filter_map(self, f: F) -> FilterMap

where Self: Sized, F: FnMut(Self::Item) -> Option,

Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate

where Self: Sized,

Creates an iterator which gives the current iteration count as well as the next value.

fn peekable(self) -> Peekable

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.

fn skip_while

(self, predicate: P) -> SkipWhile

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that skips elements based on a predicate.

fn take_while

(self, predicate: P) -> TakeWhile

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate.

fn map_while(self, predicate: P) -> MapWhile

where Self: Sized, P: FnMut(Self::Item) -> Option,

Creates an iterator that both yields elements based on a predicate and maps.

fn skip(self, n: usize) -> Skip

where Self: Sized,

Creates an iterator that skips the first n elements.

fn take(self, n: usize) -> Take

where Self: Sized,

Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner.

fn scan(self, initial_state: St, f: F) -> Scan

where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option,

An iterator adapter which, like fold, holds internal state, but unlike fold, produces a new iterator.

fn flat_map(self, f: F) -> FlatMap

where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,

Creates an iterator that works like map, but flattens nested structure.

fn flatten(self) -> Flatten

where Self: Sized, Self::Item: IntoIterator,

Creates an iterator that flattens nested structure.

fn map_windowsusize>(self, f: F) -> MapWindows

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.

fn fuse(self) -> Fuse

where Self: Sized,

Creates an iterator which ends after the first None.

fn inspect(self, f: F) -> Inspect

where Self: Sized, F: FnMut(&Self::Item),

Does something with each element of an iterator, passing the value on.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Iterator.

fn collect(self) -> B

where B: FromIteratorItem>, Self: Sized,

Transforms an iterator into a collection.

fn try_collect( &mut self, ) -> <Item as Try>::Residual as Residual>::TryType

where Self: Sized, Self::Item: Try, Item as Try>::Residual: Residual, B: FromIterator<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.

fn collect_into(self, collection: &mut E) -> &mut E

where E: ExtendItem>, Self: Sized,

🔬This is a nightly-only experimental API. (iter_collect_into #94780)

Collects all the items from an iterator into a collection.

fn partition(self, f: F) -> (B, B)

where Self: Sized, B: Default + ExtendItem>, F: FnMut(&Self::Item) -> bool,

Consumes an iterator, creating two collections from it.

fn partition_in_place<'a, T, P>(self, predicate: P) -> usize

where T: 'a, Self: Sized + DoubleEndedIterator&'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.

fn is_partitioned

(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.

fn try_fold(&mut self, init: B, f: F) -> R

where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try

,

An iterator method that applies a function as long as it returns successfully, producing a single, final value.

fn try_for_each(&mut self, f: F) -> R

where Self: Sized, F: FnMut(Self::Item) -> R, R: Try

()>,

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error.

fn fold(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.

fn reduce(self, f: F) -> OptionItem>

where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item,

Reduces the elements to a single one, by repeatedly applying a reducing operation.

fn try_reduce( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <Try>::Residual as Residual<Option<Try>::Output>>>::TryType

where Self: Sized, R: Try

Item>, Try>::Residual: Residual<OptionItem>>,

🔬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.

fn all(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if every element of the iterator matches a predicate.

fn any(&mut self, f: F) -> bool

where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if any element of the iterator matches a predicate.

fn find

(&mut self, predicate: P) -> OptionItem>

where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator that satisfies a predicate.

fn find_map(&mut self, f: F) -> Option

where Self: Sized, F: FnMut(Self::Item) -> Option,

Applies function to the elements of iterator and returns the first non-none result.

fn try_find( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <Try>::Residual as Residual<OptionItem>>>::TryType

where Self: Sized, R: Try

bool>, Try>::Residual: Residual<OptionItem>>,

🔬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.

fn position

(&mut self, predicate: P) -> Option<usize>

where Self: Sized, P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator, returning its index.

fn rposition

(&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.

fn max(self) -> OptionItem>

where Self: Sized, Self::Item: Ord,

Returns the maximum element of an iterator.

fn min(self) -> OptionItem>

where Self: Sized, Self::Item: Ord,

Returns the minimum element of an iterator.

fn max_by_key(self, f: F) -> OptionItem>

where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the maximum value from the specified function.

fn max_by(self, compare: F) -> OptionItem>

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.

fn min_by_key(self, f: F) -> OptionItem>

where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the minimum value from the specified function.

fn min_by(self, compare: F) -> OptionItem>

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.

fn rev(self) -> Rev

where Self: Sized + DoubleEndedIterator,

Reverses an iterator’s direction.

fn unzip(self) -> (FromA, FromB)

where FromA: Default + Extend, FromB: Default + Extend, Self: Sized + Iterator(A, B)>,

Converts an iterator of pairs into a pair of containers.

fn copied<'a, T>(self) -> Copied

where T: 'a + Copy, Self: Sized + Iterator&'a T>,

Creates an iterator which copies all of its elements.

fn cloned<'a, T>(self) -> Cloned

where T: 'a + Clone, Self: Sized + Iterator&'a T>,

Creates an iterator which clones all of its elements.

fn cycle(self) -> Cycle

where Self: Sized + Clone,

Repeats an iterator endlessly.

fn array_chunksusize>(self) -> ArrayChunks

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.

fn sum(self) -> S

where Self: Sized, S: SumItem>,

Sums the elements of an iterator.

fn product

(self) -> P

where Self: Sized, P: ProductItem>,

Iterates over the entire iterator, multiplying all the elements

fn cmp(self, other: I) -> Ordering

where I: IntoIteratorItem>, Self::Item: Ord, Self: Sized,

Lexicographically compares the elements of this Iterator with those of another.

fn cmp_by(self, other: I, cmp: F) -> Ordering

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, 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.

fn partial_cmp(self, other: I) -> Option<Ordering>

where I: IntoIterator, Self::Item: PartialOrd<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.

fn partial_cmp_by(self, other: I, partial_cmp: F) -> Option<Ordering>

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, 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.

fn eq(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialEq<IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are equal to those of another.

fn eq_by(self, other: I, eq: F) -> bool

where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, 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.

fn ne(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialEq<IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are not equal to those of another.

fn lt(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically less than those of another.

fn le(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically less or equal to those of another.

fn gt(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically greater than those of another.

fn ge(self, other: I) -> bool

where I: IntoIterator, Self::Item: PartialOrd<IntoIterator>::Item>, Self: Sized,

Determines if the elements of this Iterator are lexicographically greater than or equal to those of another.

fn is_sorted(self) -> bool

where Self: Sized, Self::Item: PartialOrd,

Checks if the elements of this iterator are sorted.

fn is_sorted_by(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.

fn is_sorted_by_key(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.

impl Ord for Box

where T: Ord + ?Sized, A: Allocator,

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

This method returns an Ordering between self and other.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

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

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Box

where T: PartialEq + ?Sized, A: Allocator,

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

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Box) -> bool

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

impl PartialOrd for Box

where T: PartialOrd + ?Sized, A: Allocator,

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

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Box) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Box) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn ge(&self, other: &Box) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

fn gt(&self, other: &Box) -> bool

Tests greater than (for self and other) and is used by the > operator.

impl Pointer for Box

where A: Allocator, T: ?Sized,

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

Formats the value using the given formatter.

implRead + ?Sized> Read for Box

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>

🔬This is a nightly-only experimental API. (read_buf #78485)

Pull some bytes from this source into the specified buffer.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector #69941)

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>

Reads all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize>

Reads all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>

Reads the exact number of bytes required to fill buf.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>

🔬This is a nightly-only experimental API. (read_buf #78485)

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adaptor for this instance of Read.

fn bytes(self) -> Bytes

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chainRead>(self, next: R) -> Chain

where Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.

implSeek + ?Sized> Seek for Box

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Seek to an offset, in bytes, in a stream.

fn rewind(&mut self) -> Result<()>

Rewind to the beginning of a stream.

fn stream_len(&mut self) -> Result<u64>

🔬This is a nightly-only experimental API. (seek_stream_len #59359)

Returns the length of this stream (in bytes).

fn stream_position(&mut self) -> Result<u64>

Returns the current seek position from the start of the stream.

fn seek_relative(&mut self, offset: i64) -> Result<()>

Seeks relative to the current position.

implusize> TryFrom<Box<[T]>> for Box<[T; N]>

fn try_from( boxed_slice: Box<[T]>, ) -> Result<Box<[T; N]>, <Box<[T; N]> as TryFrom<Box<[T]>>>::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.

type Error = Box<[T]>

The type returned in the event of a conversion error.

implusize> TryFrom<Vec> for Box<[T; N]>

fn try_from( vec: Vec, ) -> Result<Box<[T; N]>, <Box<[T; N]> as TryFrom<Vec>>::Error>

Attempts to convert a Vec 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 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);

type Error = Vec

The type returned in the event of a conversion error.

implWrite + ?Sized> Write for Box

fn write(&mut self, buf: &[u8]) -> Result<usize>

Writes a buffer into this writer, returning how many bytes were written.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector #69941)

Determines if this Writer has an efficient write_vectored implementation.

fn flush(&mut self) -> Result<()>

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_all(&mut self, buf: &[u8]) -> Result<()>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>

🔬This is a nightly-only experimental API. (write_all_vectored #70436)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Write.

impl CoerceUnsized<Box> for Box

where T: Unsize + ?Sized, A: Allocator, U: ?Sized,

impl DerefPure for Box

where A: Allocator, T: ?Sized,

impl DispatchFromDyn<Box> for Box

where T: Unsize + ?Sized, U: ?Sized,

impl Eq for Box

where T: Eq + ?Sized, A: Allocator,

impl FusedIterator for Box

where I: FusedIterator + ?Sized, A: Allocator,

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

where A: Allocator,

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

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

where A: Allocator,

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.

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

where A: Allocator,

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

impl PinCoerceUnsized for Box

where A: Allocator, T: ?Sized,

impl PointerLike for Box

impl Unpin for Box

where A: Allocator, T: ?Sized,