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Showing content from https://doc.rust-lang.org/nightly/alloc/boxed/struct.Box.html below:

Box in alloc::boxed - Rust

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

Attempts to downcast the box to a concrete type.

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));

Downcasts the box to a concrete type.

For a safe alternative see downcast.

#![feature(downcast_unchecked)]

use std::any::Any;

let x: Box<dyn Any> = Box::new(1_usize);

unsafe {
    assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}

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

Attempts to downcast the box to a concrete type.

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));

Downcasts the box to a concrete type.

For a safe alternative see downcast.

#![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);
}

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

Attempts to downcast the box to a concrete type.

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));

Downcasts the box to a concrete type.

For a safe alternative see downcast.

#![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);
}

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

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

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

Constructs a new box with uninitialized contents.

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

assert_eq!(*five, 5)

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.

#![feature(new_zeroed_alloc)]

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

assert_eq!(*zero, 0)

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.

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.

#![feature(allocator_api)]

let five = Box::try_new(5)?;

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

#![feature(allocator_api)]

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

assert_eq!(*five, 5);

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.

#![feature(allocator_api)]

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

assert_eq!(*zero, 0);

Allocates memory in the given allocator then places x into it.

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

#![feature(allocator_api)]

use std::alloc::System;

let five = Box::new_in(5, System);

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.

#![feature(allocator_api)]

use std::alloc::System;

let five = Box::try_new_in(5, System)?;

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

#![feature(allocator_api)]

use std::alloc::System;

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

assert_eq!(*five, 5)

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

#![feature(allocator_api)]

use std::alloc::System;

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

assert_eq!(*five, 5);

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.

#![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)

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.

#![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);

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.

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

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

Consumes the Box, returning the wrapped value.

#![feature(box_into_inner)]

let c = Box::new(5);

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

Constructs a new boxed slice with uninitialized contents.

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

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

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.

#![feature(new_zeroed_alloc)]

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

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

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

#![feature(allocator_api)]

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

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

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.

#![feature(allocator_api)]

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

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

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.

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

#![feature(allocator_api)]

use std::alloc::System;

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

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

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.

#![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])

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

#![feature(allocator_api)]

use std::alloc::System;

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

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

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.

#![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]);

Converts to Box<T, A>.

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.

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

assert_eq!(*five, 5)

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.

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

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

let big_box = Box::write(big_box, array);

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

Converts to Box<[T], A>.

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.

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

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

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 .

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.

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;
    ptr.write(5);
    let x = Box::from_raw(ptr);
}

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 .

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.

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");
    non_null.write(5);
    let x = Box::from_non_null(non_null);
}

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.

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));
}

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.

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));
}

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 .

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.

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;
    ptr.write(5);
    let x = Box::from_raw_in(ptr, System);
}

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 .

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.

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>();
    non_null.write(5);
    let x = Box::from_non_null_in(non_null, System);
}

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.

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>());
}

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.

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>());
}

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.

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);
    ptr1.write(3);
}

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.

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();
    let _val = ptr1.read();
    ptr2.write(1);
    }

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.

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.

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]);

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.

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; impl From<Box<()>> for Pin<Foo> {
    fn from(_: Box<()>) -> Pin<Foo> {
        Pin::new(Foo)
    }
}

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

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

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

Call the

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

Call the

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

Output type of the called closure’s future.

Call the

, returning a future which may move out of the called closure.

The type of items yielded by the async iterator.

Attempts to pull out the next value of this async iterator, registering the current task for wakeup if the value is not yet available, and returning

if the async iterator is exhausted.

Returns the bounds on the remaining length of the async iterator.

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

let x = Box::new([5, 6, 7]);
let mut y = Box::new([8, 9, 10]);
let yp: *const [i32] = &*y;

y.clone_from(&x);

assert_eq!(x, y);

assert_eq!(yp, &*y);

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

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

assert_eq!(x, y);

assert_ne!(&*x as *const i32, &*y as *const i32);

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

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

y.clone_from(&x);

assert_eq!(x, y);

assert_eq!(yp, &*y);

The type of value this coroutine yields.

The type of value this coroutine returns.

Resumes the execution of this coroutine.

The type of value this coroutine yields.

The type of value this coroutine returns.

Resumes the execution of this coroutine.

Creates an empty [T] inside a Box.

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

The resulting type after dereferencing.

Dereferences the value.

Mutably dereferences the value.

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

Returns the

th element from the end of the iterator.

Advances the iterator from the back by

elements.

An iterator method that reduces the iterator’s elements to a single, final value, starting from the back.

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

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

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

Returns the exact remaining length of the iterator.

Returns

if the iterator is empty.

Extends a collection with the contents of an iterator.

Extends a collection with exactly one element.

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

Performs the call operation.

Performs the call operation.

The returned type after the call operator is used.

Performs the call operation.

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

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

let slice: &[u8] = &[104, 101, 108, 108, 111];
let boxed_slice: Box<[u8]> = Box::from(slice);

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

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

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

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

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:?}");

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

Converts a &mut str into a Box<str>

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

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

Converts a str into a box of dyn Error.

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))

Converts a str into a box of dyn Error + Send + Sync.

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))

Converts a &str into a Box<str>

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

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

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

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

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

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

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

Converts to this type from the input type.

Converts to this type from the input type.

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

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

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.

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

let original: Box<i32> = Box::new(1);
let shared: Rc<i32> = Rc::from(original);
assert_eq!(1, *shared);

Converts the given boxed str slice to a String. It is notable that the str slice is owned.

let s1: String = String::from("hello world");
let s2: Box<str> = s1.into_boxed_str();
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

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

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

let boxed: Box<str> = Box::from("hello");
let boxed_str: Box<[u8]> = Box::from(boxed);

let slice: &[u8] = &[104, 101, 108, 108, 111];
let boxed_slice = Box::from(slice);

assert_eq!(boxed_slice, boxed_str);

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

When cow is the Cow::Borrowed variant, this conversion allocates on the heap and copies the underlying slice. Otherwise, it will try to reuse the owned Vec’s allocation.

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

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.

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}");

Converts a Cow into a box of dyn Error.

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))

Converts a Cow into a box of dyn Error + Send + Sync.

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))

Converts a type of Error into a box of dyn Error.

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))

Converts a type of Error + Send + Sync into a box of dyn Error + Send + Sync.

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))

Converts a String into a box of dyn Error.

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))

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

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))

Converts the given String to a boxed str slice that is owned.

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)

Converts a T into a Box<T>

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

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

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

Converts a vector into a boxed slice.

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

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());

The type of value produced on completion.

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

Returns the hash value for the values written so far.

Writes some data into this

.

Writes a single u8 into this hasher.

Writes a single u16 into this hasher.

Writes a single u32 into this hasher.

Writes a single u64 into this hasher.

Writes a single u128 into this hasher.

Writes a single usize into this hasher.

Writes a single i8 into this hasher.

Writes a single i16 into this hasher.

Writes a single i32 into this hasher.

Writes a single i64 into this hasher.

Writes a single i128 into this hasher.

Writes a single isize into this hasher.

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

Writes a single

into this hasher.

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

The type of the elements being iterated over.

Advances the iterator and returns the next value.

Returns the bounds on the remaining length of the iterator.

Returns the

th element of the iterator.

Consumes the iterator, returning the last element.

Advances the iterator and returns an array containing the next

values.

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

Advances the iterator by

elements.

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

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

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

Creates a new iterator which places a copy of

between adjacent items of the original iterator.

Creates a new iterator which places an item generated by

between adjacent items of the original iterator.

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

Calls a closure on each element of an iterator.

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

Creates an iterator that both filters and maps.

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

Creates an iterator which can use the

and

methods to look at the next element of the iterator without consuming it. See their documentation for more information.

Creates an iterator that

s elements based on a predicate.

Creates an iterator that yields elements based on a predicate.

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

Creates an iterator that skips the first

elements.

Creates an iterator that yields the first

elements, or fewer if the underlying iterator ends sooner.

An iterator adapter which, like

, holds internal state, but unlike

, produces a new iterator.

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

Creates an iterator that flattens nested structure.

Calls the given function

for each contiguous window of size

over

and returns an iterator over the outputs of

. Like

, the windows during mapping overlap as well.

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

Creates a “by reference” adapter for this instance of

.

Transforms an iterator into a collection.

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

Collects all the items from an iterator into a collection.

Consumes an iterator, creating two collections from it.

Reorders the elements of this iterator

according to the given predicate, such that all those that return

precede all those that return

. Returns the number of

elements found.

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return

precede all those that return

.

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

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

Folds every element into an accumulator by applying an operation, returning the final result.

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

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.

Tests if every element of the iterator matches a predicate.

Tests if any element of the iterator matches a predicate.

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

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

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

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

Searches for an element in an iterator from the right, returning its index.

Returns the maximum element of an iterator.

Returns the minimum element of an iterator.

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

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

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

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

Reverses an iterator’s direction.

Converts an iterator of pairs into a pair of containers.

Creates an iterator which copies all of its elements.

Returns an iterator over

elements of the iterator at a time.

Iterates over the entire iterator, multiplying all the elements

compares the

elements of this

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.

Determines if the elements of this

are equal to those of another with respect to the specified equality function.

Determines if the elements of this

are not equal to those of another.

Checks if the elements of this iterator are sorted.

Checks if the elements of this iterator are sorted using the given comparator function.

Checks if the elements of this iterator are sorted using the given key extraction function.

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

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

This method returns an ordering between

and

values if one exists.

Tests less than (for

and

) and is used by the

operator.

Tests less than or equal to (for

and

) and is used by the

operator.

Tests greater than or equal to (for

and

) and is used by the

operator.

Tests greater than (for

and

) and is used by the

operator.

Attempts to convert a Box<[T]> into a Box<[T; N]>.

The conversion occurs in-place and does not require a new memory allocation.

Returns the old Box<[T]> in the Err variant if boxed_slice.len() does not equal N.

The type returned in the event of a conversion error.

Attempts to convert a Vec<T> into a Box<[T; N]>.

Like Vec::into_boxed_slice, this is in-place if vec.capacity() == N, but will require a reallocation otherwise.

Returns the original Vec<T> in the Err variant if boxed_slice.len() does not equal N.

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);

The type returned in the event of a conversion error.

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

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.

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

Performs copy-assignment from

to

.

Converts to this type from the input type.

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The type of the item yielded by the iterator

The type of the resulting iterator

Converts self into an async iterator

The output that the future will produce on completion.

Which kind of future are we turning this into?

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Associated searcher for this pattern

Constructs the associated searcher from self and the haystack to search in.

Checks whether the pattern matches anywhere in the haystack

Checks whether the pattern matches at the front of the haystack

Removes the pattern from the front of haystack, if it matches.

Checks whether the pattern matches at the back of the haystack

Removes the pattern from the back of haystack, if it matches.

Returns the pattern as utf-8 bytes if possible.

The target type on which the method may be called.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning.

Uses borrowed data to replace owned data, usually by cloning.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

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