bones_asset::bones_utils::prelude::alloc::boxed

Struct Box

1.36.0

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§

§

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

1.0.0

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));

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.

§

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

1.0.0

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));

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.

§

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

1.51.0

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

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.

§

impl<T> Box<T>

1.0.0

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

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

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

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.

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)?;

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);

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);

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);

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);

§

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

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);

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)?;

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)

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);

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)

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);

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.

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.

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);

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);

§

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

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");

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")?;

§

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

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);

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)?;

§

impl<T> Box<[T]>

1.82.0

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

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])

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]);

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]);

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.

§

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

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])

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])

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]);

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]);

§

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

1.82.0

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

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);
}

§

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

1.82.0

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<T> Box<T>
where T: ?Sized,

1.4.0

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);
}

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

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));
}

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));
}

§

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

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);
}

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);
}

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>());
}

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>());
}

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);
}

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();
}

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

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

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);

Trait Implementations§

§

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

§

fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>

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

Attempts to allocate a block of memory. Read more

§

fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>

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

Behaves like allocate, but also ensures that the returned memory is zero-initialized. Read more

§

unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout)

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

Deallocates the memory referenced by ptr. Read more

§

unsafe fn grow( &self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout, ) -> Result<NonNull<[u8]>, AllocError>

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

Attempts to extend the memory block. Read more

§

unsafe fn grow_zeroed( &self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout, ) -> Result<NonNull<[u8]>, AllocError>

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

Behaves like grow, but also ensures that the new contents are set to zero before being returned. Read more

§

unsafe fn shrink( &self, ptr: NonNull<u8>, old_layout: Layout, new_layout: Layout, ) -> Result<NonNull<[u8]>, AllocError>

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

Attempts to shrink the memory block. Read more

§

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

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

Creates a “by reference” adapter for this instance of Allocator. Read more

1.64.0§

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

§

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

Borrows the file descriptor. Read more

1.5.0§

impl<T, A> AsMut<T> for Box<T, A>
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.

1.63.0§

impl<T> AsRawFd for Box<T>
where T: AsRawFd,

§

fn as_raw_fd(&self) -> i32

Extracts the raw file descriptor. Read more

1.5.0§

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

§

fn as_ref(&self) -> &T

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

Box

Struct Box Copy item path

Implementations§

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

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

§Examples

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

§Examples

§Safety

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

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

§Examples

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

§Examples

§Safety

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

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

§Examples

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

§Examples

§Safety

impl<T> Box<T>

pub fn new(x: T) -> Box<T>

§Examples

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

§Examples

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

§Examples

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

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

§Examples

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

§Examples

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

§Examples

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

§Examples

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

§Examples

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

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

§Examples

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

§Examples

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

§Examples

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

§Examples

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

§Examples

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

§Examples

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

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

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

§Examples

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

§Examples

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

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

§Examples

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

§Examples

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

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

§Examples

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

§Examples

impl<T> Box<[T]>

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

§Examples

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

§Examples

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

§Examples

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

§Examples

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

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

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

Struct Box

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

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

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

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

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

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

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

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

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

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>>,

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

pub fn into_pin(boxed: Box<T, A>) -> Pin<Box<T, A>>
where A: 'static,

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

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

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

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

impl<T> AsRawFd for Box<T>
where T: AsRawFd,