Box in alloc::boxed - Rust (original) (raw)
Struct Box
1.36.0 · Source
pub struct Box<T: ?Sized, A: Allocator = Global>(/* private fields */);Expand description
1.0.0 · Source
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));🔬This is a nightly-only experimental API. (downcast_unchecked #90850)
Downcasts the box to a concrete type.
For a safe alternative see downcast.
§Examples
#![feature(downcast_unchecked)]
use std::any::Any;
let x: Box<dyn Any> = Box::new(1_usize);
unsafe {
assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}§Safety
The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.
1.0.0 · Source
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));🔬This is a nightly-only experimental API. (downcast_unchecked #90850)
Downcasts the box to a concrete type.
For a safe alternative see downcast.
§Examples
#![feature(downcast_unchecked)]
use std::any::Any;
let x: Box<dyn Any + Send> = Box::new(1_usize);
unsafe {
assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}§Safety
The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.
1.51.0 · Source
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));🔬This is a nightly-only experimental API. (downcast_unchecked #90850)
Downcasts the box to a concrete type.
For a safe alternative see downcast.
§Examples
#![feature(downcast_unchecked)]
use std::any::Any;
let x: Box<dyn Any + Send + Sync> = Box::new(1_usize);
unsafe {
assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}§Safety
The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.
1.0.0 · Source
Allocates memory on the heap and then places x into it.
This doesn’t actually allocate if T is zero-sized.
§Examples
1.82.0 · Source
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)🔬This is a nightly-only experimental API. (new_zeroed_alloc #129396)
Constructs a new Box with uninitialized contents, with the memory being filled with 0 bytes.
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(new_zeroed_alloc)]
let zero = Box::<u32>::new_zeroed();
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0)1.33.0 · Source
Constructs a new Pin<Box<T>>. If T does not implement Unpin, thenx 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](struct.Box.html#method.into%5Fpin "associated function alloc::boxed::Box::into_pin")([Box::new](struct.Box.html#method.new "associated function alloc::boxed::Box::new")(x)). Consider usinginto_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.
🔬This is a nightly-only experimental API. (allocator_api #32838)
Allocates memory on the heap then places x into it, returning an error if the allocation fails
This doesn’t actually allocate if T is zero-sized.
§Examples
#![feature(allocator_api)]
let five = Box::try_new(5)?;🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new box with uninitialized contents on the heap, returning an error if the allocation fails
§Examples
#![feature(allocator_api)]
let mut five = Box::<u32>::try_new_uninit()?;
// Deferred initialization:
five.write(5);
let five = unsafe { five.assume_init() };
assert_eq!(*five, 5);🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new Box with uninitialized contents, with the memory being filled with 0 bytes on the heap
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(allocator_api)]
let zero = Box::<u32>::try_new_zeroed()?;
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0);🔬This is a nightly-only experimental API. (allocator_api #32838)
Allocates memory in the given allocator then places x into it.
This doesn’t actually allocate if T is zero-sized.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let five = Box::new_in(5, System);🔬This is a nightly-only experimental API. (allocator_api #32838)
Allocates memory in the given allocator then places x into it, returning an error if the allocation fails
This doesn’t actually allocate if T is zero-sized.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let five = Box::try_new_in(5, System)?;🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new box with uninitialized contents in the provided allocator.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let mut five = Box::<u32, _>::new_uninit_in(System);
// Deferred initialization:
five.write(5);
let five = unsafe { five.assume_init() };
assert_eq!(*five, 5)🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new box with uninitialized contents in the provided allocator, returning an error if the allocation fails
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
// Deferred initialization:
five.write(5);
let five = unsafe { five.assume_init() };
assert_eq!(*five, 5);🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new Box with uninitialized contents, with the memory being filled with 0 bytes in the provided allocator.
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let zero = Box::<u32, _>::new_zeroed_in(System);
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0)🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new Box with uninitialized contents, with the memory being filled with 0 bytes in the provided allocator, returning an error if the allocation fails,
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let zero = Box::<u32, _>::try_new_zeroed_in(System)?;
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0);🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new Pin<Box<T, A>>. If T does not implement Unpin, thenx 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](struct.Box.html#method.into%5Fpin "associated function alloc::boxed::Box::into_pin")([Box::new_in](struct.Box.html#method.new%5Fin "associated function alloc::boxed::Box::new_in")(x, alloc)). Consider usinginto_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.
🔬This is a nightly-only experimental API. (box_into_boxed_slice #71582)
Converts a Box<T> into a Box<[T]>
This conversion does not allocate on the heap and happens in place.
🔬This is a nightly-only experimental API. (box_into_inner #80437)
Consumes the Box, returning the wrapped value.
§Examples
#![feature(box_into_inner)]
let c = Box::new(5);
assert_eq!(Box::into_inner(c), 5);1.82.0 · Source
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])🔬This is a nightly-only experimental API. (new_zeroed_alloc #129396)
Constructs a new boxed slice with uninitialized contents, with the memory being filled with 0 bytes.
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(new_zeroed_alloc)]
let values = Box::<[u32]>::new_zeroed_slice(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0])🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new boxed slice with uninitialized contents. Returns an error if the allocation fails.
§Examples
#![feature(allocator_api)]
let mut values = Box::<[u32]>::try_new_uninit_slice(3)?;
// Deferred initialization:
values[0].write(1);
values[1].write(2);
values[2].write(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [1, 2, 3]);🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new boxed slice with uninitialized contents, with the memory being filled with 0 bytes. Returns an error if the allocation fails.
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(allocator_api)]
let values = Box::<[u32]>::try_new_zeroed_slice(3)?;
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0]);🔬This is a nightly-only experimental API. (slice_as_array #133508)
Converts the boxed slice into a boxed array.
This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
If N is not exactly equal to the length of self, then this method returns None.
🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new boxed slice with uninitialized contents in the provided allocator.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
// Deferred initialization:
values[0].write(1);
values[1].write(2);
values[2].write(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [1, 2, 3])🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new boxed slice with uninitialized contents in the provided allocator, with the memory being filled with 0 bytes.
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let values = Box::<[u32], _>::new_zeroed_slice_in(3, System);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0])🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new boxed slice with uninitialized contents in the provided allocator. Returns an error if the allocation fails.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let mut values = Box::<[u32], _>::try_new_uninit_slice_in(3, System)?;
// Deferred initialization:
values[0].write(1);
values[1].write(2);
values[2].write(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [1, 2, 3]);🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a new boxed slice with uninitialized contents in the provided allocator, with the memory being filled with 0 bytes. Returns an error if the allocation fails.
See MaybeUninit::zeroed for examples of correct and incorrect usage of this method.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let values = Box::<[u32], _>::try_new_zeroed_slice_in(3, System)?;
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0]);1.82.0 · Source
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)🔬This is a nightly-only experimental API. (box_uninit_write #129397)
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(box_uninit_write)]
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);
}1.82.0 · Source
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])1.4.0 · Source
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:🆕:<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);
}🔬This is a nightly-only experimental API. (box_vec_non_null #130364)
Constructs a box from a NonNull pointer.
After calling this function, the NonNull pointer is owned by the resulting Box. Specifically, the Box destructor will call the destructor of T and free the allocated memory. For this to be safe, the memory must have been allocated in accordance with the memory layout used by Box .
§Safety
This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same NonNull pointer.
The non-null pointer must point to a block of memory allocated by the global allocator.
The safety conditions are described in the memory layout section.
§Examples
Recreate a Box which was previously converted to a NonNullpointer 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:🆕:<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);
}🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a box from a raw pointer in the given allocator.
After calling this function, the raw pointer is owned by the resulting Box. Specifically, the Box destructor will call the destructor of T and free the allocated memory. For this to be safe, the memory must have been allocated in accordance with the memory layout used by Box .
§Safety
This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.
The raw pointer must point to a block of memory allocated by alloc.
§Examples
Recreate a Box which was previously converted to a raw pointer using Box::into_raw_with_allocator:
#![feature(allocator_api)]
use std::alloc::System;
let x = Box::new_in(5, System);
let (ptr, alloc) = Box::into_raw_with_allocator(x);
let x = unsafe { Box::from_raw_in(ptr, alloc) };Manually create a Box from scratch by using the system allocator:
#![feature(allocator_api, slice_ptr_get)]
use std::alloc::{Allocator, Layout, System};
unsafe {
let ptr = System.allocate(Layout:🆕:<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);
}🔬This is a nightly-only experimental API. (allocator_api #32838)
Constructs a box from a NonNull pointer in the given allocator.
After calling this function, the NonNull pointer is owned by the resulting Box. Specifically, the Box destructor will call the destructor of T and free the allocated memory. For this to be safe, the memory must have been allocated in accordance with the memory layout used by Box .
§Safety
This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.
The non-null pointer must point to a block of memory allocated by alloc.
§Examples
Recreate a Box which was previously converted to a NonNull pointer using Box::into_non_null_with_allocator:
#![feature(allocator_api, box_vec_non_null)]
use std::alloc::System;
let x = Box::new_in(5, System);
let (non_null, alloc) = Box::into_non_null_with_allocator(x);
let x = unsafe { Box::from_non_null_in(non_null, alloc) };Manually create a Box from scratch by using the system allocator:
#![feature(allocator_api, box_vec_non_null, slice_ptr_get)]
use std::alloc::{Allocator, Layout, System};
unsafe {
let non_null = System.allocate(Layout:🆕:<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);
}1.4.0 · Source
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 theBox::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_rawfor 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:🆕:<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));
}🔬This is a nightly-only experimental API. (box_vec_non_null #130364)
Consumes the Box, returning a wrapped NonNull pointer.
The pointer will be properly aligned.
After calling this function, the caller is responsible for the memory previously managed by the Box. In particular, the caller should properly destroy T and release the memory, taking into account the memory layout used by Box. The easiest way to do this is to convert the NonNull pointer back into a Box with theBox::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_nullfor 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:🆕:<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));
}🔬This is a nightly-only experimental API. (allocator_api #32838)
Consumes the Box, returning a wrapped raw pointer and the allocator.
The pointer will be properly aligned and non-null.
After calling this function, the caller is responsible for the memory previously managed by the Box. In particular, the caller should properly destroy T and release the memory, taking into account the memory layout used by Box. The easiest way to do this is to convert the raw pointer back into a Box with theBox::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_infor 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:🆕:<String>());
}🔬This is a nightly-only experimental API. (allocator_api #32838)
Consumes the Box, returning a wrapped NonNull pointer and the allocator.
The pointer will be properly aligned.
After calling this function, the caller is responsible for the memory previously managed by the Box. In particular, the caller should properly destroy T and release the memory, taking into account the memory layout used by Box. The easiest way to do this is to convert the NonNull pointer back into a Box with theBox::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 ofb.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 withBox::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:🆕:<String>());
}🔬This is a nightly-only experimental API. (box_as_ptr #129090)
Returns a raw mutable pointer to the Box’s contents.
The caller must ensure that the Box outlives the pointer this function returns, or else it will end up dangling.
This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying memory, and thus the returned pointer will remain valid when mixed with other calls to as_ptr and as_mut_ptr. Note that calling other methods that materialize references to the memory may still invalidate this pointer. See the example below for how this guarantee can be used.
§Examples
Due to the aliasing guarantee, the following code is legal:
#![feature(box_as_ptr)]
unsafe {
let mut b = Box::new(0);
let ptr1 = Box::as_mut_ptr(&mut b);
ptr1.write(1);
let ptr2 = Box::as_mut_ptr(&mut b);
ptr2.write(2);
// Notably, the write to `ptr2` did *not* invalidate `ptr1`:
ptr1.write(3);
}🔬This is a nightly-only experimental API. (box_as_ptr #129090)
Returns a raw pointer to the Box’s contents.
The caller must ensure that the Box outlives the pointer this function returns, or else it will end up dangling.
The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an UnsafeCell) using this pointer or any pointer derived from it. If you need to mutate the contents of the Box, use as_mut_ptr.
This method guarantees that for the purpose of the aliasing model, this method does not materialize a reference to the underlying memory, and thus the returned pointer will remain valid when mixed with other calls to as_ptr and as_mut_ptr. Note that calling other methods that materialize mutable references to the memory, as well as writing to this memory, may still invalidate this pointer. See the example below for how this guarantee can be used.
§Examples
Due to the aliasing guarantee, the following code is legal:
#![feature(box_as_ptr)]
unsafe {
let mut v = Box::new(0);
let ptr1 = Box::as_ptr(&v);
let ptr2 = Box::as_mut_ptr(&mut v);
let _val = ptr2.read();
// No write to this memory has happened yet, so `ptr1` is still valid.
let _val = ptr1.read();
// However, once we do a write...
ptr2.write(1);
// ... `ptr1` is no longer valid.
// This would be UB: let _val = ptr1.read();
}🔬This is a nightly-only experimental API. (allocator_api #32838)
Returns a reference to the underlying allocator.
Note: this is an associated function, which means that you have to call it as Box::allocator(&b) instead of b.allocator(). This is so that there is no conflict with a method on the inner type.
1.26.0 · Source
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 (const: unstable) · Source
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](struct.Box.html#method.new "associated function alloc::boxed::Box::new")(x))can also be written more concisely using [Box::pin](struct.Box.html#method.pin "associated function alloc::boxed::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);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.
🔬This is a nightly-only experimental API. (async_fn_traits)
Call the AsyncFn, returning a future which may borrow from the called closure.
🔬This is a nightly-only experimental API. (async_fn_traits)
🔬This is a nightly-only experimental API. (async_fn_traits)
Call the AsyncFnMut, returning a future which may borrow from the called closure.
🔬This is a nightly-only experimental API. (async_fn_traits)
Output type of the called closure’s future.
🔬This is a nightly-only experimental API. (async_fn_traits)
🔬This is a nightly-only experimental API. (async_fn_traits)
Call the AsyncFnOnce, returning a future which may move out of the called closure.
🔬This is a nightly-only experimental API. (async_iterator #79024)
The type of items yielded by the async iterator.
🔬This is a nightly-only experimental API. (async_iterator #79024)
Attempts to pull out the next value of this async iterator, registering the current task for wakeup if the value is not yet available, and returningNone if the async iterator is exhausted. Read more
🔬This is a nightly-only experimental API. (async_iterator #79024)
Returns the bounds on the remaining length of the async iterator. Read more
Copies source’s contents into self without creating a new allocation, so long as the two are of the same length.
§Examples
let x = Box::new([5, 6, 7]);
let mut y = Box::new([8, 9, 10]);
let yp: *const [i32] = &*y;
y.clone_from(&x);
// The value is the same
assert_eq!(x, y);
// And no allocation occurred
assert_eq!(yp, &*y);Returns a copy of the value. Read more
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);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);🔬This is a nightly-only experimental API. (coroutine_trait #43122)
The type of value this coroutine yields. Read more
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
The type of value this coroutine returns. Read more
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
Resumes the execution of this coroutine. Read more
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
The type of value this coroutine yields. Read more
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
The type of value this coroutine returns. Read more
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
Resumes the execution of this coroutine. Read more
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. Read more
Returns the nth element from the end of the iterator. Read more
🔬This is a nightly-only experimental API. (iter_advance_by #77404)
Advances the iterator from the back by n elements. Read more
This is the reverse version of Iterator::try_fold(): it takes elements starting from the back of the iterator. Read more
An iterator method that reduces the iterator’s elements to a single, final value, starting from the back. Read more
Searches for an element of an iterator from the back that satisfies a predicate. Read more
👎Deprecated since 1.42.0: use the Display impl or to_string()
👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
Returns the lower-level source of this error, if any. Read more
🔬This is a nightly-only experimental API. (error_generic_member_access #99301)
Provides type-based access to context intended for error reports. Read more
Returns the exact remaining length of the iterator. Read more
🔬This is a nightly-only experimental API. (exact_size_is_empty #35428)
Returns true if the iterator is empty. Read more
Extends a collection with the contents of an iterator. Read more
🔬This is a nightly-only experimental API. (extend_one #72631)
Extends a collection with exactly one element.
🔬This is a nightly-only experimental API. (extend_one #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
🔬This is a nightly-only experimental API. (fn_traits #29625)
Performs the call operation.
🔬This is a nightly-only experimental API. (fn_traits #29625)
Performs the call operation.
The returned type after the call operator is used.
🔬This is a nightly-only experimental API. (fn_traits #29625)
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.
§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:?}");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.
§Examples
// create a &mut [u8] which will be used to create a Box<[u8]>
let mut array = [104, 101, 108, 108, 111];
let slice: &mut [u8] = &mut array;
let boxed_slice: Box<[u8]> = Box::from(slice);
println!("{boxed_slice:?}");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.
§Examples
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.
§Examples
use std::error::Error;
use std::mem;
let a_str_error = "a str error";
let a_boxed_error = Box::<dyn Error>::from(a_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Converts a str into a box of dyn Error + Send + Sync.
§Examples
use std::error::Error;
use std::mem;
let a_str_error = "a str error";
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
assert!(
mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::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.
§Examples
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.
§Examples
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.
§Examples
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.
§Example
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](struct.Box.html#method.new "associated function alloc::boxed::Box::new")(x))can also be written more concisely using [Box::pin](struct.Box.html#method.pin "associated function alloc::boxed::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.
§Example
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.
§Examples
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.
§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);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 ownedVec’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 ownedString’s allocation.
§Examples
use std::borrow::Cow;
let unboxed = Cow::Borrowed("hello");
let boxed: Box<str> = Box::from(unboxed);
println!("{boxed}");let unboxed = Cow::Owned("hello".to_string());
let boxed: Box<str> = Box::from(unboxed);
println!("{boxed}");Converts a Cow into a box of dyn Error.
§Examples
use std::error::Error;
use std::mem;
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!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Converts a Cow into a box of dyn Error + Send + Sync.
§Examples
use std::error::Error;
use std::mem;
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!(
mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Converts a type of Error into a box of dyn Error.
§Examples
use std::error::Error;
use std::fmt;
use std::mem;
#[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 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error>::from(an_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Converts a type of Error + Send + Sync into a box of dyn Error + Send + Sync.
§Examples
use std::error::Error;
use std::fmt;
use std::mem;
#[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 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
assert!(
mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Converts a String into a box of dyn Error.
§Examples
use std::error::Error;
use std::mem;
let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error>::from(a_string_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Converts a String into a box of dyn Error + Send + Sync.
§Examples
use std::error::Error;
use std::mem;
let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
assert!(
mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Converts the given String to a boxed str slice that is owned.
§Examples
let s1: String = String::from("hello world");
let s2: Box<str> = Box::from(s1);
let s3: String = String::from(s2);
assert_eq!("hello world", s3)Converts a T into a Box<T>
The conversion allocates on the heap and moves tfrom the stack into it.
§Examples
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.
§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());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. Read more
Returns the hash value for the values written so far. Read more
Writes some data into this Hasher. Read more
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.
🔬This is a nightly-only experimental API. (hasher_prefixfree_extras #96762)
Writes a length prefix into this hasher, as part of being prefix-free. Read more
🔬This is a nightly-only experimental API. (hasher_prefixfree_extras #96762)
Writes a single str into this hasher. Read more
Which kind of iterator are we turning this into?
The type of the elements being iterated over.
Creates an iterator from a value. Read more
Which kind of iterator are we turning this into?
The type of the elements being iterated over.
Creates an iterator from a value. Read more
Which kind of iterator are we turning this into?
The type of the elements being iterated over.
Creates an iterator from a value. Read more
The type of the elements being iterated over.
Advances the iterator and returns the next value. Read more
Returns the bounds on the remaining length of the iterator. Read more
Returns the nth element of the iterator. Read more
Consumes the iterator, returning the last element. Read more
🔬This is a nightly-only experimental API. (iter_next_chunk #98326)
Advances the iterator and returns an array containing the next N values. Read more
Consumes the iterator, counting the number of iterations and returning it. Read more
🔬This is a nightly-only experimental API. (iter_advance_by #77404)
Advances the iterator by n elements. Read more
Creates an iterator starting at the same point, but stepping by the given amount at each iteration. Read more
Takes two iterators and creates a new iterator over both in sequence. Read more
‘Zips up’ two iterators into a single iterator of pairs. Read more
🔬This is a nightly-only experimental API. (iter_intersperse #79524)
Creates a new iterator which places a copy of separator between adjacent items of the original iterator. Read more
🔬This is a nightly-only experimental API. (iter_intersperse #79524)
Creates a new iterator which places an item generated by separatorbetween adjacent items of the original iterator. Read more
Takes a closure and creates an iterator which calls that closure on each element. Read more
Calls a closure on each element of an iterator. Read more
Creates an iterator which uses a closure to determine if an element should be yielded. Read more
Creates an iterator that both filters and maps. Read more
Creates an iterator which gives the current iteration count as well as the next value. Read more
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
Creates an iterator that skips elements based on a predicate. Read more
Creates an iterator that yields elements based on a predicate. Read more
Creates an iterator that both yields elements based on a predicate and maps. Read more
Creates an iterator that skips the first n elements. Read more
Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner. Read more
An iterator adapter which, like fold, holds internal state, but unlike fold, produces a new iterator. Read more
Creates an iterator that works like map, but flattens nested structure. Read more
Creates an iterator that flattens nested structure. Read more
🔬This is a nightly-only experimental API. (iter_map_windows #87155)
Calls the given function f for each contiguous window of size N overself and returns an iterator over the outputs of f. Like slice::windows(), the windows during mapping overlap as well. Read more
Creates an iterator which ends after the first None. Read more
Does something with each element of an iterator, passing the value on. Read more
Borrows an iterator, rather than consuming it. Read more
Transforms an iterator into a collection. Read more
🔬This is a nightly-only experimental API. (iterator_try_collect #94047)
Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered. Read more
🔬This is a nightly-only experimental API. (iter_collect_into #94780)
Collects all the items from an iterator into a collection. Read more
Consumes an iterator, creating two collections from it. Read more
🔬This is a nightly-only experimental API. (iter_partition_in_place #62543)
Reorders the elements of this iterator in-place according to the given predicate, such that all those that return true precede all those that return false. Returns the number of true elements found. Read more
🔬This is a nightly-only experimental API. (iter_is_partitioned #62544)
Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false. Read more
An iterator method that applies a function as long as it returns successfully, producing a single, final value. Read more
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
Folds every element into an accumulator by applying an operation, returning the final result. Read more
Reduces the elements to a single one, by repeatedly applying a reducing operation. Read more
🔬This is a nightly-only experimental API. (iterator_try_reduce #87053)
Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately. Read more
Tests if every element of the iterator matches a predicate. Read more
Tests if any element of the iterator matches a predicate. Read more
Searches for an element of an iterator that satisfies a predicate. Read more
Applies function to the elements of iterator and returns the first non-none result. Read more
🔬This is a nightly-only experimental API. (try_find #63178)
Applies function to the elements of iterator and returns the first true result or the first error. Read more
Searches for an element in an iterator, returning its index. Read more
Searches for an element in an iterator from the right, returning its index. Read more
Returns the maximum element of an iterator. Read more
Returns the minimum element of an iterator. Read more
Returns the element that gives the maximum value from the specified function. Read more
Returns the element that gives the maximum value with respect to the specified comparison function. Read more
Returns the element that gives the minimum value from the specified function. Read more
Returns the element that gives the minimum value with respect to the specified comparison function. Read more
Reverses an iterator’s direction. Read more
Converts an iterator of pairs into a pair of containers. Read more
Creates an iterator which copies all of its elements. Read more
Creates an iterator which clones all of its elements. Read more
Repeats an iterator endlessly. Read more
🔬This is a nightly-only experimental API. (iter_array_chunks #100450)
Returns an iterator over N elements of the iterator at a time. Read more
Sums the elements of an iterator. Read more
Iterates over the entire iterator, multiplying all the elements Read more
🔬This is a nightly-only experimental API. (iter_order_by #64295)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more
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
🔬This is a nightly-only experimental API. (iter_order_by #64295)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more
Determines if the elements of this Iterator are equal to those of another. Read more
🔬This is a nightly-only experimental API. (iter_order_by #64295)
Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function. Read more
Determines if the elements of this Iterator are not equal to those of another. Read more
Checks if the elements of this iterator are sorted. Read more
Checks if the elements of this iterator are sorted using the given comparator function. Read more
Checks if the elements of this iterator are sorted using the given key extraction function. Read more
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 self and other values if one exists. Read more
Tests less than (for self and other) and is used by the < operator. Read more
Tests less than or equal to (for self and other) and is used by the<= operator. Read more
Tests greater than or equal to (for self and other) and is used by the >= operator. Read more
Tests greater than (for self and other) and is used by the >operator. Read more
Attempts to convert a Box<[T]> into a Box<[T; N]>.
The conversion occurs in-place and does not require a new memory allocation.
§Errors
Returns the old Box<[T]> in the Err variant ifboxed_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.
§Errors
Returns the original Vec<T> in the Err variant ifboxed_slice.len() does not equal N.
§Examples
This can be used with vec! to create an array on the heap:
let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap();
assert_eq!(state.len(), 100);The type returned in the event of a conversion error.
This implementation is required to make sure that the &Box<[I]>: IntoIteratorimplementation doesn’t overlap with IntoIterator for T where T: Iterator blanket.
This implementation is required to make sure that the &mut Box<[I]>: IntoIteratorimplementation doesn’t overlap with IntoIterator for T where T: Iterator blanket.
This implementation is required to make sure that the Box<[I]>: IntoIteratorimplementation doesn’t overlap with IntoIterator for T where T: Iterator blanket.
🔬This is a nightly-only experimental API. (clone_to_uninit #126799)
Performs copy-assignment from self to dst. Read more
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](../../core/convert/trait.From.html "trait core::convert::From")<T> for U chooses to do.
🔬This is a nightly-only experimental API. (async_iterator #79024)
The type of the item yielded by the iterator
🔬This is a nightly-only experimental API. (async_iterator #79024)
The type of the resulting iterator
🔬This is a nightly-only experimental API. (async_iterator #79024)
Converts self into an async iterator
The output that the future will produce on completion.
Which kind of future are we turning this into?
Creates a future from a value. Read more
The type of the elements being iterated over.
Which kind of iterator are we turning this into?
Creates an iterator from a value. Read more
🔬This is a nightly-only experimental API. (pattern #27721)
Associated searcher for this pattern
🔬This is a nightly-only experimental API. (pattern #27721)
Constructs the associated searcher fromself and the haystack to search in.
🔬This is a nightly-only experimental API. (pattern #27721)
Checks whether the pattern matches anywhere in the haystack
🔬This is a nightly-only experimental API. (pattern #27721)
Checks whether the pattern matches at the front of the haystack
🔬This is a nightly-only experimental API. (pattern #27721)
Removes the pattern from the front of haystack, if it matches.
🔬This is a nightly-only experimental API. (pattern #27721)
Checks whether the pattern matches at the back of the haystack
🔬This is a nightly-only experimental API. (pattern #27721)
Removes the pattern from the back of haystack, if it matches.
🔬This is a nightly-only experimental API. (pattern #27721)
Returns the pattern as utf-8 bytes if possible.
🔬This is a nightly-only experimental API. (arbitrary_self_types #44874)
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. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
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.