Struct Box

1.55.0 · Source

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

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> Box<dyn Any, A>
where A: Allocator,

1.0.0 · Source

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

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

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> Box<dyn Any + Send, A>
where A: Allocator,

1.0.0 · Source

pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + 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::<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>(self) -> Box<T, A>
where T: Any,

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

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

1.51.0 · Source

pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send + Sync, 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::<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>(self) -> Box<T, A>
where T: Any,

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

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) -> Box<T>

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)

1.92.0 · Source

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

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

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<Box<T>, AllocError>

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

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)

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)

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

pub fn map(this: Box<T>, f: impl FnOnce(T) -> U) -> Box

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

Maps the value in a box, reusing the allocation if possible.

f is called on the value in the box, and the result is returned, also boxed.

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

§Examples

#![feature(smart_pointer_try_map)]

let b = Box::new(7);
let new = Box::map(b, |i| i + 7);
assert_eq!(*new, 14);

Source

pub fn try_map<R>( this: Box<T>, f: impl FnOnce(T) -> R, ) -> <<R as Try>::Residual as Residual<Box<<R as Try>::Output>>>::TryType
where R: Try, <R as Try>::Residual: Residual<Box<<R as Try>::Output>>,

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

Attempts to map the value in a box, reusing the allocation if possible.

f is called on the value in the box, and if the operation succeeds, the result is returned, also boxed.

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

§Examples

#![feature(smart_pointer_try_map)]

let b = Box::new(7);
let new = Box::try_map(b, u32::try_from).unwrap();
assert_eq!(*new, 7);

Source §

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

Source

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

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

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<Box<T, A>, AllocError>
where A: Allocator,

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

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)

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)

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)

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)

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<Box<T, A>>
where A: 'static + Allocator,

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

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: Box<T, A>) -> Box<[T], A>

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

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: Box<T, A>) -> T

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

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

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

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

Consumes the Box without consuming its allocation, returning the wrapped value and a Box to the uninitialized memory where the wrapped value used to live.

This can be used together with write to reuse the allocation for multiple boxed values.

§Examples

#![feature(box_take)]

let c = Box::new(5);

// take the value out of the box
let (value, uninit) = Box::take(c);
assert_eq!(value, 5);

// reuse the box for a second value
let c = Box::write(uninit, 6);
assert_eq!(*c, 6);

Source §

impl<T> Box<T>
where T: CloneToUninit + ?Sized,

Source

pub fn clone_from_ref(src: &T) -> Box<T>

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

Allocates memory on the heap then clones src into it.

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

§Examples

#![feature(clone_from_ref)]

let hello: Box<str> = Box::clone_from_ref("hello");

Source

pub fn try_clone_from_ref(src: &T) -> Result<Box<T>, AllocError>

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

Allocates memory on the heap then clones src into it, returning an error if allocation fails.

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

§Examples

#![feature(clone_from_ref)]
#![feature(allocator_api)]

let hello: Box<str> = Box::try_clone_from_ref("hello")?;

Source §

impl<T, A> Box<T, A>
where T: CloneToUninit + ?Sized, A: Allocator,

Source

pub fn clone_from_ref_in(src: &T, alloc: A) -> Box<T, A>

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

Allocates memory in the given allocator then clones src into it.

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

§Examples

#![feature(clone_from_ref)]
#![feature(allocator_api)]

use std::alloc::System;

let hello: Box<str, System> = Box::clone_from_ref_in("hello", System);

Source

pub fn try_clone_from_ref_in(src: &T, alloc: A) -> Result<Box<T, A>, AllocError>

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

Allocates memory in the given allocator then clones src into it, returning an error if allocation fails.

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

§Examples

#![feature(clone_from_ref)]
#![feature(allocator_api)]

use std::alloc::System;

let hello: Box<str, System> = Box::try_clone_from_ref_in("hello", System)?;

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])

1.92.0 · Source

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

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

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)

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)

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. (alloc_slice_into_array)

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> Box<[T], A>
where A: Allocator,

Source

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

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

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)

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)

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)

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> Box<MaybeUninit<T>, A>
where A: Allocator,

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: Box<MaybeUninit<T>, A>, 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> Box<[MaybeUninit<T>], A>
where A: Allocator,

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> Box<T>
where T: ?Sized,

1.4.0 · Source

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

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>) -> Box<T>

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

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);
}

1.4.0 · Source

pub fn into_raw(b: Box<T>) -> *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: Box<T>) -> NonNull<T>

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

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 §

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

Source

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

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

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) -> Box<T, A>

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

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);
}

Source

pub fn into_raw_with_allocator(b: Box<T, A>) -> (*mut T, A)

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

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: Box<T, A>) -> (NonNull<T>, A)

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

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 Box<T, A>) -> *mut T

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

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: &Box<T, A>) -> *const T

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

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: &Box<T, A>) -> &A

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

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: Box<T, A>) -> &'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: Box<T, A>) -> Pin<Box<T, A>>
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);

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

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

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

Available on non-no_global_oom_handling only.

Source §

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

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: &Box<T, A>)

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>

Available on non-no_global_oom_handling only.

Source §

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

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

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

Available on non-no_global_oom_handling only.

fn deserialize<D>( deserializer: D, ) -> Result<Box<RawValue>, <D as Deserializer<'de>>::Error>
where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more

Source §

impl<'de, T> Deserialize<'de> for Box<T>
where T: Deserialize<'de>,

Available on crate features std or alloc only.

Source §

fn deserialize<D>( deserializer: D, ) -> Result<Box<T>, <D as Deserializer<'de>>::Error>
where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more

Source §

impl<'de> Deserialize<'de> for Box<str>

Available on crate features std or alloc only.

Returns the nth 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)

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

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)

Provides type-based access to context intended for error reports. Read more

1.0.0 · Source§

fn description(&self) -> &str

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

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

Source §

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

Source §

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

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

Performs the call operation.

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

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

Performs the call operation.

1.17.0 · Source§

impl<T> From<&[T]> for Box<[T]>
where T: Clone,

Available on non-no_global_oom_handling only.

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.

1.17.0 · Source§

impl From<&OsStr> for Box<OsStr>

Source §

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

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

impl<T> From<&Slice<T>> for Box<Slice<T>>
where T: Copy,

Source §

fn from(slice: &Slice<T>) -> Box<Slice<T>>

Converts to this type from the input type.

1.84.0 · Source§

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

Available on non-no_global_oom_handling only.

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:?}");

This will allocate and clone path to it.

1.84.0 · Source§

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

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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]>

Available on non-no_global_oom_handling only.

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:?}");

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

Panics if the pointer (the Box) is not properly aligned.

§Examples

use crossbeam_epoch::Owned;

let o = unsafe { Owned::from_raw(Box::into_raw(Box::new(1234))) };

Source §

impl<T> From<Box<T>> for RBox<T>

Source §

fn from(this: Box<T>) -> RBox<T> ⓘ

Converts to this type from the input type.

1.21.0 · Source§

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

Available on non-no_global_oom_handling only.

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

Source §

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

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, A> From<Box<T, A>> for Rc<T, A>
where A: Allocator, T: ?Sized,

Available on non-no_global_oom_handling only.

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);

1.19.0 · Source§

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

Source §

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

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> From<Cow<'_, [T]>> for Box<[T]>
where T: Clone,

Available on non-no_global_oom_handling only.

Source §

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

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

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

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

1.45.0 · Source§

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

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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

Available on non-no_global_oom_handling only.

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

Available on non-no_global_oom_handling only.

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))

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

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

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>

Available on non-no_global_oom_handling only.

Source §

fn from(t: T) -> Box<T>

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

Available on non-no_global_oom_handling only.

Source §

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

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)

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. (iter_next_chunk)

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)

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(self, other: U) -> Chain<Self, ::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(self, other: U) -> Zip<Self, ::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)

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)

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

Transforms an iterator into a collection. Read more

Source §

fn try_collect( &mut self, ) -> <<Self::Item as Try>::Residual as Residual>::TryType
where Self: Sized, Self::Item: Try, <Self::Item as Try>::Residual: Residual, B: FromIterator<<Self::Item as Try>::Output>,

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

Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered. Read more

Source §

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)

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

Source §

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)

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

Source §

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)

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

Source §

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)

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

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

Source §

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)

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

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 collect_array<const N: usize>(self) -> Option<[Self::Item; N]>
where Self: Sized,

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

Checks if an iterator has exactly N elements. If so, returns those N elements in an array. Read more

1.0.0 · Source§

automatically converts the parser’s output and error values to another type, as long as they implement the From trait

1.0.0 · Source§

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

Source §

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

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

Source §

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

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

1.0.0 · Source§

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

Pull some bytes from this source into the specified buffer. Read more

Source §

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

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

Source §

fn is_read_vectored(&self) -> bool

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

Determines if this Reader has an efficient read_vectored implementation. Read more

Source §

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

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

Source §

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

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

Source §

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

Reads the exact number of bytes required to fill buf. Read more

Source §

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

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

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

Source §

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

Rewind to the beginning of a stream. Read more

Source §

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

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

Returns the length of this stream (in bytes). Read more

Source §

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

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

Source §

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

Seeks relative to the current position. Read more

Source §

impl<T> Serialize for Box<T>
where T: Serialize + ?Sized,

Available on crate features std or alloc only.

Source §

fn serialize<S>( &self, serializer: S, ) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>
where S: Serializer,

Serialize this value into the given Serde serializer. Read more

1.43.0 · Source§

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);

Source §

type Error = Vec<T>

The type returned in the event of a conversion error.

1.0.0 · Source§

impl<W> Write for Box<W>
where W: Write + ?Sized,

Source §

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

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

Source §

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

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

Source §

fn is_write_vectored(&self) -> bool

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

Determines if this Writer has an efficient write_vectored implementation. Read more

Source §

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

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

Source §

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

Attempts to write an entire buffer into this writer. Read more

Source §

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

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

1.0.0 · Source§

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

1.26.0 · Source§

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

1.80.0 · Source§

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.

1.80.0 · Source§

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.

1.80.0 · Source§

impl<I, A> !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.