pub struct Box<T, A = Global>(/* private fields */)
where
A: Allocator,
T: ?Sized;
Expand description
A pointer type that uniquely owns a heap allocation of type T
.
See the module-level documentation for more.
Implementations§
source§impl<T> Box<T>
impl<T> Box<T>
sourcepub fn new_uninit() -> Box<MaybeUninit<T>>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub fn new_uninit() -> Box<MaybeUninit<T>>
new_uninit
#63291)sourcepub fn new_zeroed() -> Box<MaybeUninit<T>>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub fn new_zeroed() -> Box<MaybeUninit<T>>
new_uninit
#63291)Constructs a new Box
with uninitialized contents, with the memory
being filled with 0
bytes.
See MaybeUninit::zeroed
for examples of correct and incorrect usage
of this method.
§Examples
#![feature(new_uninit)]
let zero = Box::<u32>::new_zeroed();
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0)
Run1.33.0 · sourcepub fn pin(x: T) -> Pin<Box<T>>
pub fn pin(x: T) -> Pin<Box<T>>
Constructs a new Pin<Box<T>>
. If T
does not implement Unpin
, then
x
will be pinned in memory and unable to be moved.
Constructing and pinning of the Box
can also be done in two steps: Box::pin(x)
does the same as Box::into_pin(Box::new(x))
. Consider using
into_pin
if you already have a Box<T>
, or if you want to
construct a (pinned) Box
in a different way than with Box::new
.
sourcepub fn try_new(x: T) -> Result<Box<T>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new(x: T) -> Result<Box<T>, AllocError>
allocator_api
#32838)sourcepub fn try_new_uninit() -> Result<Box<MaybeUninit<T>>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_uninit() -> Result<Box<MaybeUninit<T>>, AllocError>
allocator_api
#32838)Constructs a new box with uninitialized contents on the heap, returning an error if the allocation fails
§Examples
#![feature(allocator_api, new_uninit)]
let mut five = Box::<u32>::try_new_uninit()?;
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5);
Runsourcepub fn try_new_zeroed() -> Result<Box<MaybeUninit<T>>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_zeroed() -> Result<Box<MaybeUninit<T>>, AllocError>
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, new_uninit)]
let zero = Box::<u32>::try_new_zeroed()?;
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0);
Runsource§impl<T, A> Box<T, A>where
A: Allocator,
impl<T, A> Box<T, A>where
A: Allocator,
sourcepub fn new_in(x: T, alloc: A) -> Box<T, A>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn new_in(x: T, alloc: A) -> Box<T, A>where
A: Allocator,
allocator_api
#32838)sourcepub fn try_new_in(x: T, alloc: A) -> Result<Box<T, A>, AllocError>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_in(x: T, alloc: A) -> Result<Box<T, A>, AllocError>where
A: Allocator,
allocator_api
#32838)sourcepub fn new_uninit_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn new_uninit_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
allocator_api
#32838)Constructs a new box with uninitialized contents in the provided allocator.
§Examples
#![feature(allocator_api, new_uninit)]
use std::alloc::System;
let mut five = Box::<u32, _>::new_uninit_in(System);
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5)
Runsourcepub fn try_new_uninit_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_uninit_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where
A: Allocator,
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, new_uninit)]
use std::alloc::System;
let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5);
Runsourcepub fn new_zeroed_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn new_zeroed_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
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, new_uninit)]
use std::alloc::System;
let zero = Box::<u32, _>::new_zeroed_in(System);
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0)
Runsourcepub fn try_new_zeroed_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_zeroed_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where
A: Allocator,
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, new_uninit)]
use std::alloc::System;
let zero = Box::<u32, _>::try_new_zeroed_in(System)?;
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0);
Runsourcepub fn pin_in(x: T, alloc: A) -> Pin<Box<T, A>>where
A: 'static + Allocator,
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn pin_in(x: T, alloc: A) -> Pin<Box<T, A>>where
A: 'static + Allocator,
allocator_api
#32838)Constructs a new Pin<Box<T, A>>
. If T
does not implement Unpin
, then
x
will be pinned in memory and unable to be moved.
Constructing and pinning of the Box
can also be done in two steps: Box::pin_in(x, alloc)
does the same as Box::into_pin(Box::new_in(x, alloc))
. Consider using
into_pin
if you already have a Box<T, A>
, or if you want to
construct a (pinned) Box
in a different way than with Box::new_in
.
source§impl<T> Box<[T]>
impl<T> Box<[T]>
sourcepub fn new_uninit_slice(len: usize) -> Box<[MaybeUninit<T>]>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub fn new_uninit_slice(len: usize) -> Box<[MaybeUninit<T>]>
new_uninit
#63291)Constructs a new boxed slice with uninitialized contents.
§Examples
#![feature(new_uninit)]
let mut values = Box::<[u32]>::new_uninit_slice(3);
let values = unsafe {
// Deferred initialization:
values[0].as_mut_ptr().write(1);
values[1].as_mut_ptr().write(2);
values[2].as_mut_ptr().write(3);
values.assume_init()
};
assert_eq!(*values, [1, 2, 3])
Runsourcepub fn new_zeroed_slice(len: usize) -> Box<[MaybeUninit<T>]>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub fn new_zeroed_slice(len: usize) -> Box<[MaybeUninit<T>]>
new_uninit
#63291)Constructs a new boxed slice with uninitialized contents, with the memory
being filled with 0
bytes.
See MaybeUninit::zeroed
for examples of correct and incorrect usage
of this method.
§Examples
#![feature(new_uninit)]
let values = Box::<[u32]>::new_zeroed_slice(3);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0])
Runsourcepub fn try_new_uninit_slice(
len: usize
) -> Result<Box<[MaybeUninit<T>]>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_uninit_slice( len: usize ) -> Result<Box<[MaybeUninit<T>]>, AllocError>
allocator_api
#32838)Constructs a new boxed slice with uninitialized contents. Returns an error if the allocation fails
§Examples
#![feature(allocator_api, new_uninit)]
let mut values = Box::<[u32]>::try_new_uninit_slice(3)?;
let values = unsafe {
// Deferred initialization:
values[0].as_mut_ptr().write(1);
values[1].as_mut_ptr().write(2);
values[2].as_mut_ptr().write(3);
values.assume_init()
};
assert_eq!(*values, [1, 2, 3]);
Runsourcepub fn try_new_zeroed_slice(
len: usize
) -> Result<Box<[MaybeUninit<T>]>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn try_new_zeroed_slice( len: usize ) -> Result<Box<[MaybeUninit<T>]>, AllocError>
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, new_uninit)]
let values = Box::<[u32]>::try_new_zeroed_slice(3)?;
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0]);
Runsource§impl<T, A> Box<[T], A>where
A: Allocator,
impl<T, A> Box<[T], A>where
A: Allocator,
sourcepub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[MaybeUninit<T>], A>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[MaybeUninit<T>], A>
allocator_api
#32838)Constructs a new boxed slice with uninitialized contents in the provided allocator.
§Examples
#![feature(allocator_api, new_uninit)]
use std::alloc::System;
let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
let values = unsafe {
// Deferred initialization:
values[0].as_mut_ptr().write(1);
values[1].as_mut_ptr().write(2);
values[2].as_mut_ptr().write(3);
values.assume_init()
};
assert_eq!(*values, [1, 2, 3])
Runsourcepub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[MaybeUninit<T>], A>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[MaybeUninit<T>], A>
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, new_uninit)]
use std::alloc::System;
let values = Box::<[u32], _>::new_zeroed_slice_in(3, System);
let values = unsafe { values.assume_init() };
assert_eq!(*values, [0, 0, 0])
Runsource§impl<T, A> Box<MaybeUninit<T>, A>where
A: Allocator,
impl<T, A> Box<MaybeUninit<T>, A>where
A: Allocator,
sourcepub unsafe fn assume_init(self) -> Box<T, A>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub unsafe fn assume_init(self) -> Box<T, A>
new_uninit
#63291)Converts to Box<T, A>
.
§Safety
As with MaybeUninit::assume_init
,
it is up to the caller to guarantee that the value
really is in an initialized state.
Calling this when the content is not yet fully initialized
causes immediate undefined behavior.
§Examples
#![feature(new_uninit)]
let mut five = Box::<u32>::new_uninit();
let five: Box<u32> = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5)
Runsourcepub fn write(boxed: Box<MaybeUninit<T>, A>, value: T) -> Box<T, A>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub fn write(boxed: Box<MaybeUninit<T>, A>, value: T) -> Box<T, A>
new_uninit
#63291)Writes the value and converts to Box<T, A>
.
This method converts the box similarly to Box::assume_init
but
writes value
into it before conversion thus guaranteeing safety.
In some scenarios use of this method may improve performance because
the compiler may be able to optimize copying from stack.
§Examples
#![feature(new_uninit)]
let big_box = Box::<[usize; 1024]>::new_uninit();
let mut array = [0; 1024];
for (i, place) in array.iter_mut().enumerate() {
*place = i;
}
// The optimizer may be able to elide this copy, so previous code writes
// to heap directly.
let big_box = Box::write(big_box, array);
for (i, x) in big_box.iter().enumerate() {
assert_eq!(*x, i);
}
Runsource§impl<T, A> Box<[MaybeUninit<T>], A>where
A: Allocator,
impl<T, A> Box<[MaybeUninit<T>], A>where
A: Allocator,
sourcepub unsafe fn assume_init(self) -> Box<[T], A>
🔬This is a nightly-only experimental API. (new_uninit
#63291)
pub unsafe fn assume_init(self) -> Box<[T], A>
new_uninit
#63291)Converts to Box<[T], A>
.
§Safety
As with MaybeUninit::assume_init
,
it is up to the caller to guarantee that the values
really are in an initialized state.
Calling this when the content is not yet fully initialized
causes immediate undefined behavior.
§Examples
#![feature(new_uninit)]
let mut values = Box::<[u32]>::new_uninit_slice(3);
let values = unsafe {
// Deferred initialization:
values[0].as_mut_ptr().write(1);
values[1].as_mut_ptr().write(2);
values[2].as_mut_ptr().write(3);
values.assume_init()
};
assert_eq!(*values, [1, 2, 3])
Runsource§impl<T> Box<T>where
T: ?Sized,
impl<T> Box<T>where
T: ?Sized,
1.4.0 · sourcepub unsafe fn from_raw(raw: *mut T) -> Box<T>
pub unsafe fn from_raw(raw: *mut T) -> Box<T>
Constructs a box from a raw pointer.
After calling this function, the raw pointer is owned by the
resulting Box
. Specifically, the Box
destructor will call
the destructor of T
and free the allocated memory. For this
to be safe, the memory must have been allocated in accordance
with the memory layout used by Box
.
§Safety
This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.
The 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) };
RunManually create a Box
from scratch by using the global allocator:
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
// In general .write is required to avoid attempting to destruct
// the (uninitialized) previous contents of `ptr`, though for this
// simple example `*ptr = 5` would have worked as well.
ptr.write(5);
let x = Box::from_raw(ptr);
}
Runsource§impl<T, A> Box<T, A>
impl<T, A> Box<T, A>
const: unstable · sourcepub unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Box<T, A>
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Box<T, A>
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.
§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) };
RunManually create a Box
from scratch by using the system allocator:
#![feature(allocator_api, slice_ptr_get)]
use std::alloc::{Allocator, Layout, System};
unsafe {
let ptr = System.allocate(Layout::new::<i32>())?.as_mut_ptr() as *mut i32;
// In general .write is required to avoid attempting to destruct
// the (uninitialized) previous contents of `ptr`, though for this
// simple example `*ptr = 5` would have worked as well.
ptr.write(5);
let x = Box::from_raw_in(ptr, System);
}
Run1.4.0 · sourcepub fn into_raw(b: Box<T, A>) -> *mut T
pub fn into_raw(b: Box<T, A>) -> *mut T
Consumes the Box
, returning a wrapped raw pointer.
The pointer will be properly aligned and non-null.
After calling this function, the caller is responsible for the
memory previously managed by the Box
. In particular, the
caller should properly destroy T
and release the memory, taking
into account the memory layout used by Box
. The easiest way to
do this is to convert the raw pointer back into a Box
with the
Box::from_raw
function, allowing the Box
destructor to perform
the cleanup.
Note: this is an associated function, which means that you have
to call it as Box::into_raw(b)
instead of b.into_raw()
. This
is so that there is no conflict with a method on the inner type.
§Examples
Converting the raw pointer back into a Box
with Box::from_raw
for automatic cleanup:
let x = Box::new(String::from("Hello"));
let ptr = Box::into_raw(x);
let x = unsafe { Box::from_raw(ptr) };
RunManual 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>());
}
RunNote: 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));
}
Runsourcepub fn into_raw_with_allocator(b: Box<T, A>) -> (*mut T, A)
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn into_raw_with_allocator(b: Box<T, A>) -> (*mut T, A)
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 the
Box::from_raw_in
function, allowing the Box
destructor to perform
the cleanup.
Note: this is an associated function, which means that you have
to call it as Box::into_raw_with_allocator(b)
instead of b.into_raw_with_allocator()
. This
is so that there is no conflict with a method on the inner type.
§Examples
Converting the raw pointer back into a Box
with Box::from_raw_in
for automatic cleanup:
#![feature(allocator_api)]
use std::alloc::System;
let x = Box::new_in(String::from("Hello"), System);
let (ptr, alloc) = Box::into_raw_with_allocator(x);
let x = unsafe { Box::from_raw_in(ptr, alloc) };
RunManual 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>());
}
Runconst: unstable · sourcepub fn allocator(b: &Box<T, A>) -> &A
🔬This is a nightly-only experimental API. (allocator_api
#32838)
pub fn allocator(b: &Box<T, A>) -> &A
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 · sourcepub fn leak<'a>(b: Box<T, A>) -> &'a mut Twhere
A: 'a,
pub fn leak<'a>(b: Box<T, A>) -> &'a mut Twhere
A: 'a,
Consumes and leaks the Box
, returning a mutable reference,
&'a mut T
. Note that the type T
must outlive the chosen lifetime
'a
. If the type has only static references, or none at all, then this
may be chosen to be 'static
.
This function is mainly useful for data that lives for the remainder of
the program’s life. Dropping the returned reference will cause a memory
leak. If this is not acceptable, the reference should first be wrapped
with the Box::from_raw
function producing a Box
. This Box
can
then be dropped which will properly destroy T
and release the
allocated memory.
Note: this is an associated function, which means that you have
to call it as Box::leak(b)
instead of b.leak()
. This
is so that there is no conflict with a method on the inner type.
§Examples
Simple usage:
let x = Box::new(41);
let static_ref: &'static mut usize = Box::leak(x);
*static_ref += 1;
assert_eq!(*static_ref, 42);
RunUnsized 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]);
Run1.63.0 (const: unstable) · sourcepub fn into_pin(boxed: Box<T, A>) -> Pin<Box<T, A>>where
A: 'static,
pub fn into_pin(boxed: Box<T, A>) -> Pin<Box<T, A>>where
A: 'static,
Converts a Box<T>
into a Pin<Box<T>>
. If T
does not implement Unpin
, then
*boxed
will be pinned in memory and unable to be moved.
This conversion does not allocate on the heap and happens in place.
This is also available via From
.
Constructing and pinning a Box
with Box::into_pin(Box::new(x))
can also be written more concisely using Box::pin(x)
.
This into_pin
method is useful if you already have a Box<T>
, or you are
constructing a (pinned) Box
in a different way than with Box::new
.
§Notes
It’s not recommended that crates add an impl like From<Box<T>> for Pin<T>
,
as it’ll introduce an ambiguity when calling Pin::from
.
A demonstration of such a poor impl is shown below.
source§impl<A> Box<dyn Any, A>where
A: Allocator,
impl<A> Box<dyn Any, A>where
A: Allocator,
sourcepub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any, A>>where
T: Any,
pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any, A>>where
T: Any,
Attempt to downcast the box to a concrete type.
§Examples
use std::any::Any;
fn print_if_string(value: Box<dyn Any>) {
if let Ok(string) = value.downcast::<String>() {
println!("String ({}): {}", string.len(), string);
}
}
let my_string = "Hello World".to_string();
print_if_string(Box::new(my_string));
print_if_string(Box::new(0i8));
Runsourcepub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
T: Any,
🔬This is a nightly-only experimental API. (downcast_unchecked
#90850)
pub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
T: Any,
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);
}
Run§Safety
The contained value must be of type T
. Calling this method
with the incorrect type is undefined behavior.
source§impl<A> Box<dyn Any + Send, A>where
A: Allocator,
impl<A> Box<dyn Any + Send, A>where
A: Allocator,
sourcepub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send, A>>where
T: Any,
pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send, A>>where
T: Any,
Attempt to downcast the box to a concrete type.
§Examples
use std::any::Any;
fn print_if_string(value: Box<dyn Any + Send>) {
if let Ok(string) = value.downcast::<String>() {
println!("String ({}): {}", string.len(), string);
}
}
let my_string = "Hello World".to_string();
print_if_string(Box::new(my_string));
print_if_string(Box::new(0i8));
Runsourcepub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
T: Any,
🔬This is a nightly-only experimental API. (downcast_unchecked
#90850)
pub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
T: Any,
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);
}
Run§Safety
The contained value must be of type T
. Calling this method
with the incorrect type is undefined behavior.
source§impl<A> Box<dyn Any + Send + Sync, A>where
A: Allocator,
impl<A> Box<dyn Any + Send + Sync, A>where
A: Allocator,
1.51.0 · sourcepub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send + Sync, A>>where
T: Any,
pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send + Sync, A>>where
T: Any,
Attempt to downcast the box to a concrete type.
§Examples
use std::any::Any;
fn print_if_string(value: Box<dyn Any + Send + Sync>) {
if let Ok(string) = value.downcast::<String>() {
println!("String ({}): {}", string.len(), string);
}
}
let my_string = "Hello World".to_string();
print_if_string(Box::new(my_string));
print_if_string(Box::new(0i8));
Runsourcepub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
T: Any,
🔬This is a nightly-only experimental API. (downcast_unchecked
#90850)
pub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
T: Any,
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);
}
Run§Safety
The contained value must be of type T
. Calling this method
with the incorrect type is undefined behavior.
Trait Implementations§
1.64.0 · source§impl<T: AsFd> AsFd for Box<T>
impl<T: AsFd> AsFd for Box<T>
source§fn as_fd(&self) -> BorrowedFd<'_>
fn as_fd(&self) -> BorrowedFd<'_>
1.71.0 · source§impl<T: AsHandle> AsHandle for Box<T>
Available on Windows only.
impl<T: AsHandle> AsHandle for Box<T>
source§fn as_handle(&self) -> BorrowedHandle<'_>
fn as_handle(&self) -> BorrowedHandle<'_>
1.71.0 · source§impl<T: AsSocket> AsSocket for Box<T>
Available on Windows only.
impl<T: AsSocket> AsSocket for Box<T>
source§fn as_socket(&self) -> BorrowedSocket<'_>
fn as_socket(&self) -> BorrowedSocket<'_>
source§impl<S> AsyncIterator for Box<S>
impl<S> AsyncIterator for Box<S>
§type Item = <S as AsyncIterator>::Item
type Item = <S as AsyncIterator>::Item
async_iterator
#79024)source§fn poll_next(
self: Pin<&mut Box<S>>,
cx: &mut Context<'_>
) -> Poll<Option<<Box<S> as AsyncIterator>::Item>>
fn poll_next( self: Pin<&mut Box<S>>, cx: &mut Context<'_> ) -> Poll<Option<<Box<S> as AsyncIterator>::Item>>
async_iterator
#79024)None
if the async iterator is exhausted. Read more1.1.0 · source§impl<T, A> BorrowMut<T> for Box<T, A>
impl<T, A> BorrowMut<T> for Box<T, A>
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<B: BufRead + ?Sized> BufRead for Box<B>
impl<B: BufRead + ?Sized> BufRead for Box<B>
source§fn fill_buf(&mut self) -> Result<&[u8]>
fn fill_buf(&mut self) -> Result<&[u8]>
source§fn consume(&mut self, amt: usize)
fn consume(&mut self, amt: usize)
amt
bytes have been consumed from the buffer,
so they should no longer be returned in calls to read
. Read moresource§fn read_line(&mut self, buf: &mut String) -> Result<usize>
fn read_line(&mut self, buf: &mut String) -> Result<usize>
0xA
byte) is reached, and append
them to the provided String
buffer. Read moresource§fn has_data_left(&mut self) -> Result<bool>
fn has_data_left(&mut self) -> Result<bool>
buf_read_has_data_left
#86423)Read
has any data left to be read. Read moresource§fn skip_until(&mut self, byte: u8) -> Result<usize>
fn skip_until(&mut self, byte: u8) -> Result<usize>
bufread_skip_until
#111735)byte
or EOF is reached. Read moresource§impl<T, A> Clone for Box<T, A>
impl<T, A> Clone for Box<T, A>
source§impl<G, R, A> Coroutine<R> for Box<G, A>
impl<G, R, A> Coroutine<R> for Box<G, A>
§type Yield = <G as Coroutine<R>>::Yield
type Yield = <G as Coroutine<R>>::Yield
coroutine_trait
#43122)source§impl<G, R, A> Coroutine<R> for Pin<Box<G, A>>
impl<G, R, A> Coroutine<R> for Pin<Box<G, A>>
§type Yield = <G as Coroutine<R>>::Yield
type Yield = <G as Coroutine<R>>::Yield
coroutine_trait
#43122)source§impl<I, A> DoubleEndedIterator for Box<I, A>
impl<I, A> DoubleEndedIterator for Box<I, A>
source§fn next_back(&mut self) -> Option<<I as Iterator>::Item>
fn next_back(&mut self) -> Option<<I as Iterator>::Item>
source§fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>
fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>
n
th element from the end of the iterator. Read moresource§fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
iter_advance_by
#77404)n
elements. Read more1.27.0 · source§fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
Iterator::try_fold()
: it takes
elements starting from the back of the iterator. Read more1.8.0 · source§impl<T> Error for Box<T>where
T: Error,
impl<T> Error for Box<T>where
T: Error,
source§fn description(&self) -> &str
fn description(&self) -> &str
source§fn cause(&self) -> Option<&dyn Error>
fn cause(&self) -> Option<&dyn Error>
source§impl<I, A> ExactSizeIterator for Box<I, A>
impl<I, A> ExactSizeIterator for Box<I, A>
1.45.0 · source§impl Extend<Box<str>> for String
impl Extend<Box<str>> for String
1.17.0 · source§impl<T> From<&[T]> for Box<[T]>where
T: Clone,
impl<T> From<&[T]> for Box<[T]>where
T: Clone,
source§fn from(slice: &[T]) -> Box<[T]>
fn from(slice: &[T]) -> Box<[T]>
Converts a &[T]
into a Box<[T]>
This conversion allocates on the heap
and performs a copy of slice
and its contents.
§Examples
// create a &[u8] which will be used to create a Box<[u8]>
let slice: &[u8] = &[104, 101, 108, 108, 111];
let boxed_slice: Box<[u8]> = Box::from(slice);
println!("{boxed_slice:?}");
Runsource§impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a>
impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a>
source§fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a>
fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a>
Converts a str
into a box of dyn Error
+ Send
+ Sync
.
§Examples
use std::error::Error;
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))
Run1.33.0 · source§impl<T, A> From<Box<T, A>> for Pin<Box<T, A>>
impl<T, A> From<Box<T, A>> for Pin<Box<T, A>>
source§fn from(boxed: Box<T, A>) -> Pin<Box<T, A>>
fn from(boxed: Box<T, A>) -> Pin<Box<T, A>>
Converts a Box<T>
into a Pin<Box<T>>
. If T
does not implement Unpin
, then
*boxed
will be pinned in memory and unable to be moved.
This conversion does not allocate on the heap and happens in place.
This is also available via Box::into_pin
.
Constructing and pinning a Box
with <Pin<Box<T>>>::from(Box::new(x))
can also be written more concisely using Box::pin(x)
.
This From
implementation is useful if you already have a Box<T>
, or you are
constructing a (pinned) Box
in a different way than with Box::new
.
1.19.0 · source§impl<A> From<Box<str, A>> for Box<[u8], A>where
A: Allocator,
impl<A> From<Box<str, A>> for Box<[u8], A>where
A: Allocator,
source§fn from(s: Box<str, A>) -> Box<[u8], A>
fn from(s: Box<str, A>) -> Box<[u8], A>
Converts a Box<str>
into a Box<[u8]>
This conversion does not allocate on the heap and happens in place.
§Examples
// create a Box<str> which will be used to create a Box<[u8]>
let boxed: Box<str> = Box::from("hello");
let boxed_str: Box<[u8]> = Box::from(boxed);
// create a &[u8] which will be used to create a Box<[u8]>
let slice: &[u8] = &[104, 101, 108, 108, 111];
let boxed_slice = Box::from(slice);
assert_eq!(boxed_slice, boxed_str);
Run1.45.0 · source§impl From<Cow<'_, str>> for Box<str>
impl From<Cow<'_, str>> for Box<str>
source§fn from(cow: Cow<'_, str>) -> Box<str>
fn from(cow: Cow<'_, str>) -> Box<str>
Converts a Cow<'_, str>
into a Box<str>
When cow
is the Cow::Borrowed
variant, this
conversion allocates on the heap and copies the
underlying str
. Otherwise, it will try to reuse the owned
String
’s allocation.
§Examples
use std::borrow::Cow;
let unboxed = Cow::Borrowed("hello");
let boxed: Box<str> = Box::from(unboxed);
println!("{boxed}");
Runlet unboxed = Cow::Owned("hello".to_string());
let boxed: Box<str> = Box::from(unboxed);
println!("{boxed}");
Run1.22.0 · source§impl<'a> From<Cow<'a, str>> for Box<dyn Error>
impl<'a> From<Cow<'a, str>> for Box<dyn Error>
1.22.0 · source§impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a>
impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a>
source§fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a>
fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a>
Converts a Cow
into a box of dyn Error
+ Send
+ Sync
.
§Examples
use std::error::Error;
use std::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))
Runsource§impl<'a, E> From<E> for Box<dyn Error + 'a>where
E: Error + 'a,
impl<'a, E> From<E> for Box<dyn Error + 'a>where
E: Error + 'a,
source§fn from(err: E) -> Box<dyn Error + 'a>
fn from(err: E) -> Box<dyn Error + 'a>
Converts a type of Error
into a box of dyn Error
.
§Examples
use std::error::Error;
use std::fmt;
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))
Runsource§impl<'a, E> From<E> for Box<dyn Error + Send + Sync + 'a>
impl<'a, E> From<E> for Box<dyn Error + Send + Sync + 'a>
source§fn from(err: E) -> Box<dyn Error + Send + Sync + 'a>
fn from(err: E) -> Box<dyn Error + Send + Sync + 'a>
Converts a type of Error
+ Send
+ Sync
into a box of
dyn Error
+ Send
+ Sync
.
§Examples
use std::error::Error;
use std::fmt;
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))
Run1.6.0 · source§impl From<String> for Box<dyn Error>
impl From<String> for Box<dyn Error>
source§impl From<String> for Box<dyn Error + Send + Sync>
impl From<String> for Box<dyn Error + Send + Sync>
source§fn from(err: String) -> Box<dyn Error + Send + Sync>
fn from(err: String) -> Box<dyn Error + Send + Sync>
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))
Run1.20.0 · source§impl<T, A> From<Vec<T, A>> for Box<[T], A>where
A: Allocator,
impl<T, A> From<Vec<T, A>> for Box<[T], A>where
A: Allocator,
source§fn from(v: Vec<T, A>) -> Box<[T], A>
fn from(v: Vec<T, A>) -> Box<[T], A>
Convert 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());
RunAny 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());
Run1.32.0 · source§impl<I> FromIterator<I> for Box<[I]>
impl<I> FromIterator<I> for Box<[I]>
1.22.0 · source§impl<T, A> Hasher for Box<T, A>
impl<T, A> Hasher for Box<T, A>
source§fn write_u128(&mut self, i: u128)
fn write_u128(&mut self, i: u128)
u128
into this hasher.source§fn write_usize(&mut self, i: usize)
fn write_usize(&mut self, i: usize)
usize
into this hasher.source§fn write_i128(&mut self, i: i128)
fn write_i128(&mut self, i: i128)
i128
into this hasher.source§fn write_isize(&mut self, i: isize)
fn write_isize(&mut self, i: isize)
isize
into this hasher.source§impl<I, A> Iterator for Box<I, A>
impl<I, A> Iterator for Box<I, A>
source§fn next(&mut self) -> Option<<I as Iterator>::Item>
fn next(&mut self) -> Option<<I as Iterator>::Item>
source§fn size_hint(&self) -> (usize, Option<usize>)
fn size_hint(&self) -> (usize, Option<usize>)
source§fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item>
fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item>
n
th element of the iterator. Read moresource§fn last(self) -> Option<<I as Iterator>::Item>
fn last(self) -> Option<<I as Iterator>::Item>
source§fn next_chunk<const N: usize>(
&mut self
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
Self: Sized,
fn next_chunk<const N: usize>(
&mut self
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
Self: Sized,
iter_next_chunk
#98326)N
values. Read moresource§fn count(self) -> usizewhere
Self: Sized,
fn count(self) -> usizewhere
Self: Sized,
source§fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
iter_advance_by
#77404)n
elements. Read more1.28.0 · source§fn step_by(self, step: usize) -> StepBy<Self> ⓘwhere
Self: Sized,
fn step_by(self, step: usize) -> StepBy<Self> ⓘwhere
Self: Sized,
source§fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> ⓘ
fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> ⓘ
source§fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> ⓘwhere
Self: Sized,
U: IntoIterator,
fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> ⓘwhere
Self: Sized,
U: IntoIterator,
source§fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
iter_intersperse
#79524)separator
between adjacent items of the original iterator. Read moresource§fn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
fn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
source§fn filter<P>(self, predicate: P) -> Filter<Self, P> ⓘ
fn filter<P>(self, predicate: P) -> Filter<Self, P> ⓘ
source§fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
source§fn enumerate(self) -> Enumerate<Self> ⓘwhere
Self: Sized,
fn enumerate(self) -> Enumerate<Self> ⓘwhere
Self: Sized,
source§fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
source§fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
1.57.0 · source§fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
source§fn skip(self, n: usize) -> Skip<Self> ⓘwhere
Self: Sized,
fn skip(self, n: usize) -> Skip<Self> ⓘwhere
Self: Sized,
n
elements. Read moresource§fn take(self, n: usize) -> Take<Self> ⓘwhere
Self: Sized,
fn take(self, n: usize) -> Take<Self> ⓘwhere
Self: Sized,
n
elements, or fewer
if the underlying iterator ends sooner. Read moresource§fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> ⓘ
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> ⓘ
source§fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
iter_map_windows
#87155)f
for each contiguous window of size N
over
self
and returns an iterator over the outputs of f
. Like slice::windows()
,
the windows during mapping overlap as well. Read moresource§fn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
fn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
source§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
source§fn collect_into<E>(self, collection: &mut E) -> &mut E
fn collect_into<E>(self, collection: &mut E) -> &mut E
iter_collect_into
#94780)source§fn partition<B, F>(self, f: F) -> (B, B)
fn partition<B, F>(self, f: F) -> (B, B)
source§fn is_partitioned<P>(self, predicate: P) -> bool
fn is_partitioned<P>(self, predicate: P) -> bool
iter_is_partitioned
#62544)true
precede all those that return false
. Read more1.27.0 · source§fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
1.27.0 · source§fn try_for_each<F, R>(&mut self, f: F) -> R
fn try_for_each<F, R>(&mut self, f: F) -> R
source§fn fold<B, F>(self, init: B, f: F) -> B
fn fold<B, F>(self, init: B, f: F) -> B
1.51.0 · source§fn reduce<F>(self, f: F) -> Option<Self::Item>
fn reduce<F>(self, f: F) -> Option<Self::Item>
source§fn try_reduce<F, R>(
&mut self,
f: F
) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
fn try_reduce<F, R>( &mut self, f: F ) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
iterator_try_reduce
#87053)source§fn all<F>(&mut self, f: F) -> bool
fn all<F>(&mut self, f: F) -> bool
source§fn any<F>(&mut self, f: F) -> bool
fn any<F>(&mut self, f: F) -> bool
source§fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
1.30.0 · source§fn find_map<B, F>(&mut self, f: F) -> Option<B>
fn find_map<B, F>(&mut self, f: F) -> Option<B>
source§fn try_find<F, R>(
&mut self,
f: F
) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
fn try_find<F, R>( &mut self, f: F ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
try_find
#63178)source§fn position<P>(&mut self, predicate: P) -> Option<usize>
fn position<P>(&mut self, predicate: P) -> Option<usize>
1.6.0 · source§fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>
fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>
1.15.0 · source§fn max_by<F>(self, compare: F) -> Option<Self::Item>
fn max_by<F>(self, compare: F) -> Option<Self::Item>
1.6.0 · source§fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>
fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>
1.15.0 · source§fn min_by<F>(self, compare: F) -> Option<Self::Item>
fn min_by<F>(self, compare: F) -> Option<Self::Item>
source§fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
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fn copied<'a, T>(self) -> Copied<Self> ⓘ
source§fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘwhere
Self: Sized,
fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘwhere
Self: Sized,
iter_array_chunks
#100450)N
elements of the iterator at a time. Read more1.11.0 · source§fn product<P>(self) -> P
fn product<P>(self) -> P
source§fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
iter_order_by
#64295)Iterator
with those
of another with respect to the specified comparison function. Read more1.5.0 · source§fn partial_cmp<I>(self, other: I) -> Option<Ordering>
fn partial_cmp<I>(self, other: I) -> Option<Ordering>
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 moresource§fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>where
Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,
fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>where
Self: Sized,
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,
iter_order_by
#64295)Iterator
with those
of another with respect to the specified comparison function. Read moresource§fn eq_by<I, F>(self, other: I, eq: F) -> bool
fn eq_by<I, F>(self, other: I, eq: F) -> bool
iter_order_by
#64295)1.5.0 · source§fn lt<I>(self, other: I) -> bool
fn lt<I>(self, other: I) -> bool
Iterator
are lexicographically
less than those of another. Read more1.5.0 · source§fn le<I>(self, other: I) -> bool
fn le<I>(self, other: I) -> bool
Iterator
are lexicographically
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fn gt<I>(self, other: I) -> bool
Iterator
are lexicographically
greater than those of another. Read more1.5.0 · source§fn ge<I>(self, other: I) -> bool
fn ge<I>(self, other: I) -> bool
Iterator
are lexicographically
greater than or equal to those of another. Read moresource§fn is_sorted_by<F>(self, compare: F) -> bool
fn is_sorted_by<F>(self, compare: F) -> bool
is_sorted
#53485)source§impl<T, A> Ord for Box<T, A>
impl<T, A> Ord for Box<T, A>
source§impl<T, A> PartialEq for Box<T, A>
impl<T, A> PartialEq for Box<T, A>
source§impl<T, A> PartialOrd for Box<T, A>
impl<T, A> PartialOrd for Box<T, A>
source§fn le(&self, other: &Box<T, A>) -> bool
fn le(&self, other: &Box<T, A>) -> bool
self
and other
) and is used by the <=
operator. Read moresource§impl<R: Read + ?Sized> Read for Box<R>
impl<R: Read + ?Sized> Read for Box<R>
source§fn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
source§fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
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#78485)source§fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
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#69941)source§fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
buf
. Read moresource§fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read moresource§fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read moresource§fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)cursor
. Read moresource§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Read
. Read moresource§impl<S: Seek + ?Sized> Seek for Box<S>
impl<S: Seek + ?Sized> Seek for Box<S>
source§fn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
source§fn stream_position(&mut self) -> Result<u64>
fn stream_position(&mut self) -> Result<u64>
1.43.0 · source§impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]>
impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]>
source§fn try_from(
boxed_slice: Box<[T]>
) -> Result<Box<[T; N]>, <Box<[T; N]> as TryFrom<Box<[T]>>>::Error>
fn try_from( boxed_slice: Box<[T]> ) -> Result<Box<[T; N]>, <Box<[T; N]> as TryFrom<Box<[T]>>>::Error>
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 if
boxed_slice.len()
does not equal N
.
1.66.0 · source§impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]>
impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]>
source§fn try_from(
vec: Vec<T>
) -> Result<Box<[T; N]>, <Box<[T; N]> as TryFrom<Vec<T>>>::Error>
fn try_from( vec: Vec<T> ) -> Result<Box<[T; N]>, <Box<[T; N]> as TryFrom<Vec<T>>>::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 if
boxed_slice.len()
does not equal N
.
§Examples
This can be used with vec!
to create an array on the heap:
let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap();
assert_eq!(state.len(), 100);
Runsource§impl<W: Write + ?Sized> Write for Box<W>
impl<W: Write + ?Sized> Write for Box<W>
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
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#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
impl<T, U, A> CoerceUnsized<Box<U, A>> for Box<T, A>
impl<T, U> DispatchFromDyn<Box<U>> for Box<T>
impl<T, A> Eq for Box<T, A>
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impl<T, A> Unpin for Box<T, A>
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§type Item = <I as AsyncIterator>::Item
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#79024)§type IntoAsyncIter = I
type IntoAsyncIter = I
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#79024)source§fn into_async_iter(self) -> <I as IntoAsyncIterator>::IntoAsyncIter
fn into_async_iter(self) -> <I as IntoAsyncIterator>::IntoAsyncIter
async_iterator
#79024)self
into an async iteratorsource§impl<F> IntoFuture for Fwhere
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§type IntoFuture = F
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fn into_future(self) -> <F as IntoFuture>::IntoFuture
source§impl<I> IntoIterator for Iwhere
I: Iterator,
impl<I> IntoIterator for Iwhere
I: Iterator,
source§impl<'a, F> Pattern<'a> for F
impl<'a, F> Pattern<'a> for F
§type Searcher = CharPredicateSearcher<'a, F>
type Searcher = CharPredicateSearcher<'a, F>
pattern
#27721)source§fn into_searcher(self, haystack: &'a str) -> CharPredicateSearcher<'a, F>
fn into_searcher(self, haystack: &'a str) -> CharPredicateSearcher<'a, F>
pattern
#27721)self
and the haystack
to search in.source§fn is_contained_in(self, haystack: &'a str) -> bool
fn is_contained_in(self, haystack: &'a str) -> bool
pattern
#27721)source§fn is_prefix_of(self, haystack: &'a str) -> bool
fn is_prefix_of(self, haystack: &'a str) -> bool
pattern
#27721)source§fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str>
fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str>
pattern
#27721)source§fn is_suffix_of(self, haystack: &'a str) -> boolwhere
CharPredicateSearcher<'a, F>: ReverseSearcher<'a>,
fn is_suffix_of(self, haystack: &'a str) -> boolwhere
CharPredicateSearcher<'a, F>: ReverseSearcher<'a>,
pattern
#27721)source§fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>where
CharPredicateSearcher<'a, F>: ReverseSearcher<'a>,
fn strip_suffix_of(self, haystack: &'a str) -> Option<&'a str>where
CharPredicateSearcher<'a, F>: ReverseSearcher<'a>,
pattern
#27721)