Struct allocator_api2 :: stable :: boxed :: Box Copy item path

impl<T> Box<T>

pub fn new(x: T) -> Self

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

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

§Examples

let five = Box::new(5);

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

Constructs a new box with uninitialized contents.

§Examples

#![feature(new_uninit)]

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

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

    five.assume_init()
};

assert_eq!(*five, 5)

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

#![feature(new_uninit)]

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

assert_eq!(*zero, 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<Self, AllocError>

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>

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

§Examples

#![feature(allocator_api, new_uninit)]

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

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

    five.assume_init()
};

assert_eq!(*five, 5);

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

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

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

§Examples

#![feature(allocator_api, new_uninit)]

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

assert_eq!(*zero, 0);

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

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

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<Self, AllocError>
where A: Allocator,

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,

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

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

    five.assume_init()
};

assert_eq!(*five, 5)

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

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

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

    five.assume_init()
};

assert_eq!(*five, 5);

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

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

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

assert_eq!(*zero, 0)

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

Constructs a new Box with uninitialized contents, with the memory being filled with 0 bytes in the provided allocator, returning an error if the allocation fails,

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

assert_eq!(*zero, 0);

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

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: Self) -> Box<[T], A> ⓘ

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: Self) -> T

Consumes the Box, returning the wrapped value.

§Examples

#![feature(box_into_inner)]

let c = Box::new(5);

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

impl<T> Box<[T]>

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

Constructs a new boxed slice with uninitialized contents.

§Examples

#![feature(new_uninit)]

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

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

    values.assume_init()
};

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

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

#![feature(new_uninit)]

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>

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

§Examples

#![feature(allocator_api, new_uninit)]

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

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

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

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

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

§Examples

#![feature(allocator_api, new_uninit)]

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

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

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

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

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

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

    values.assume_init()
};

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

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

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

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

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

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

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

§Examples

#![feature(allocator_api, new_uninit)]

use std::alloc::System;

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

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

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

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, new_uninit)]

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]);

pub fn into_vec(self) -> Vec<T, A>
where A: Allocator,

Converts self into a vector without clones or allocation.

The resulting vector can be converted back into a box via Vec<T>’s into_boxed_slice method.

§Examples

let s: Box<[i32]> = Box::new([10, 40, 30]);
let x = s.into_vec();
// `s` cannot be used anymore because it has been converted into `x`.

assert_eq!(x, vec![10, 40, 30]);

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

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

#![feature(new_uninit)]

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

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

    five.assume_init()
};

assert_eq!(*five, 5)

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

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

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

§Examples

#![feature(new_uninit)]

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

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

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

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

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

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

#![feature(new_uninit)]

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

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

    values.assume_init()
};

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

impl<T: ?Sized> Box<T>

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

Constructs a box from a raw pointer.

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

§Safety

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

The safety conditions are described in the memory layout section.

§Examples

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

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

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);
}

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

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

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

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

§Safety

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

§Examples

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

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:

use allocator_api2::alloc::{Allocator, Layout, System};

unsafe {
    let ptr = System.allocate(Layout::new::<i32>())?.as_ptr().cast::<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 fn into_raw(b: Self) -> *mut T

Consumes the Box, returning a wrapped raw pointer.

The pointer will be properly aligned and non-null.

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

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

§Examples

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

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

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

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

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

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

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(b: Self) -> (NonNull<T>, A)

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

Returns a reference to the underlying allocator.

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

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

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

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

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

§Examples

Simple usage:

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

Unsized data:

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

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

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

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

This is also available via From.

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

§Notes

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

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

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

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

Attempt to downcast the box to a concrete type.

§Examples

use std::any::Any;

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

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

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

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

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

Attempt to downcast the box to a concrete type.

§Examples

use std::any::Any;

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

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

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

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

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

Attempt to downcast the box to a concrete type.

§Examples

use std::any::Any;

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

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

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

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.

Trait Implementations§

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

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

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

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

fn as_ref(&self) -> &T

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

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

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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

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

Mutably borrows from an owned value. Read more

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

type Item = ::Item

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

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

fn clone(&self) -> Self

Returns a copy of the value. Read more

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

Performs copy-assignment from source. Read more

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

fn clone(&self) -> Self

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

§Examples

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

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

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

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

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

§Examples

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

y.clone_from(&x);

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

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

impl Clone for Box<str>

fn clone(&self) -> Self

Returns a copy 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: Debug + ?Sized, A: Allocator> Debug for Box<T, A>

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

Formats the value using the given formatter. Read more

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

fn default() -> Self

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

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

fn default() -> Self

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

impl<A: Allocator + Default> Default for Box<str, A>

fn default() -> Self

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

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

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

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

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

Mutably dereferences the value.

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

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

Formats the value using the given formatter. Read more

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

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

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

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

Returns the nth element from the end of the iterator. Read more

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

1.27.0 · source§

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

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

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

fn drop(&mut self)

Executes the destructor for this type. Read more

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

fn len(&self) -> usize

Returns the exact remaining length of the iterator. Read more

fn is_empty(&self) -> bool

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

Returns true if the iterator is empty. Read more

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

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

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

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

Reserves capacity in a collection for the given number of additional elements. Read more

impl<T: Copy, A: Allocator + Default> From<&[T]> for Box<[T], A>

fn from(slice: &[T]) -> Box<[T], A> ⓘ

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

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

§Examples

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

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

impl<A: Allocator + Default> From<&str> for Box<str, A>

fn from(s: &str) -> Box<str, A> ⓘ

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}");

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

fn from(array: [T; N]) -> Box<[T]> ⓘ

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

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

§Examples

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

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

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

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

§Examples

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

impl<T, A: Allocator, const N: usize> From<Box<[T; N], A>> for Vec<T, A>

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

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

§Examples

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

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

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

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

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

This is also available via Box::into_pin.

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

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

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

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

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

§Examples

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

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

assert_eq!(boxed_slice, boxed_str);

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

fn from(t: T) -> Self

Converts a T into a Box<T>

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

§Examples

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

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

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

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

Convert a vector into a boxed slice.

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

§Examples

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

Any excess capacity is removed:

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

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

impl FromIterator for Box<[I]>

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

Creates a value from an iterator. Read more

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

type Output = <F as Future>::Output

The type of value produced on completion.

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

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

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

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

Feeds this value into the given Hasher. Read more

1.3.0 · source§

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

Feeds a slice of this type into the given Hasher. Read more

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

fn finish(&self) -> u64

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

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

Writes some data into this Hasher. Read more

fn write_u8(&mut self, i: u8)

Writes a single u8 into this hasher.

fn write_u16(&mut self, i: u16)

Writes a single u16 into this hasher.

fn write_u32(&mut self, i: u32)

Writes a single u32 into this hasher.

fn write_u64(&mut self, i: u64)

Writes a single u64 into this hasher.

fn write_u128(&mut self, i: u128)

Writes a single u128 into this hasher.

fn write_usize(&mut self, i: usize)

Writes a single usize into this hasher.

fn write_i8(&mut self, i: i8)

Writes a single i8 into this hasher.

fn write_i16(&mut self, i: i16)

Writes a single i16 into this hasher.

fn write_i32(&mut self, i: i32)

Writes a single i32 into this hasher.

fn write_i64(&mut self, i: i64)

Writes a single i64 into this hasher.

fn write_i128(&mut self, i: i128)

Writes a single i128 into this hasher.

fn write_isize(&mut self, i: isize)

Writes a single isize into this hasher.

fn write_length_prefix(&mut self, len: usize)

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

Writes a length prefix into this hasher, as part of being prefix-free. Read more

fn write_str(&mut self, s: &str)

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

Writes a single str into this hasher. Read more

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

type Item = ::Item

The type of the elements being iterated over.

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

Advances the iterator and returns the next value. Read more

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

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

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

Returns the nth element of the iterator. Read more

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

Consumes the iterator, returning the last element. Read more

fn next_chunk<const N: usize>( &mut self, ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>
where Self: Sized,

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

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

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

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)

Creates a new iterator which places an item generated by separator between adjacent items of the original iterator. Read more

1.0.0 · source§

fn map<B, F>(self, f: F) -> Map<Self, F>
where Self: Sized, F: FnMut(Self::Item) -> B,

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

1.21.0 · source§

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

Calls a closure on each element of an iterator. Read more

1.0.0 · source§

fn filter(self, predicate: P) -> Filter<Self, P>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

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

1.0.0 · source§

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
where Self: Sized, F: FnMut(Self::Item) -> Option,

Creates an iterator that both filters and maps. Read more

1.0.0 · source§

fn enumerate(self) -> Enumerate<Self>
where Self: Sized,

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

1.0.0 · source§

fn peekable(self) -> Peekable<Self>
where Self: Sized,

Creates an iterator which can use the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information. Read more

1.0.0 · source§

fn skip_while(self, predicate: P) -> SkipWhile<Self, P>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that skips elements based on a predicate. Read more

1.0.0 · source§

fn take_while(self, predicate: P) -> TakeWhile<Self, P>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate. Read more

1.57.0 · source§

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

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

1.0.0 · source§

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

Creates an iterator that skips the first n elements. Read more

1.0.0 · source§

fn take(self, n: usize) -> Take<Self>
where Self: Sized,

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

1.0.0 · source§

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option,

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

1.0.0 · source§

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,

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

fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N>
where Self: Sized, F: FnMut(&[Self::Item; N]) -> R,

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

Calls the given function f for each contiguous window of size N over self and returns an iterator over the outputs of f. Like slice::windows(), the windows during mapping overlap as well. Read more

1.0.0 · source§

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

Creates an iterator which ends after the first None. Read more

1.0.0 · source§

fn inspect<F>(self, f: F) -> Inspect<Self, F>
where Self: Sized, F: FnMut(&Self::Item),

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

1.0.0 · source§

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

Borrows an iterator, rather than consuming it. 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

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

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

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

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

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

fn try_find<F, R>( &mut self, f: F, ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
where Self: Sized, F: FnMut(&Self::Item) -> R, R: Try<Output = bool>, <R as Try>::Residual: Residual<Option<Self::Item>>,

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

Applies function to the elements of iterator and returns the first true result or the first error. Read more

1.0.0 · source§

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

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

1.6.0 · source§

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

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

1.15.0 · source§

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

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

1.6.0 · source§

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

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

1.15.0 · source§

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

Returns the element that gives the minimum value with respect to the specified comparison function. Read more

1.0.0 · source§

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
where FromA: Default + Extend<A>, FromB: Default + Extend, Self: Sized + Iterator<Item = (A, B)>,

Converts an iterator of pairs into a pair of containers. Read more

1.36.0 · source§

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

Creates an iterator which copies all of its elements. Read more

1.0.0 · source§

fn cloned<'a, T>(self) -> Cloned<Self>
where T: 'a + Clone, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which clones all of its elements. Read more

fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>
where Self: Sized,

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

Iterates over the entire iterator, multiplying all the elements Read more

fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, ::Item) -> Ordering,

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

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more

1.5.0 · source§

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

Lexicographically compares the PartialOrd elements of this Iterator with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned. Read more