pub type ErasedBoxCart = Box<dyn ErasedDestructor>;
Expand description
A type-erased Cart that has Box
semantics
See the docs of Yoke::erase_box_cart()
for more info.
✨ Enabled with the alloc
Cargo feature.
Aliased Type§
struct ErasedBoxCart(/* private fields */);
Implementations
Source§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 raw pointer must point to a block of memory allocated by the global allocator.
The safety conditions are described in the memory layout section.
§Examples
Recreate a Box
which was previously converted to a raw pointer
using Box::into_raw
:
let x = Box::new(5);
let ptr = Box::into_raw(x);
let x = unsafe { Box::from_raw(ptr) };
Manually create a Box
from scratch by using the global allocator:
use std::alloc::{alloc, Layout};
unsafe {
let ptr = alloc(Layout::new::<i32>()) as *mut i32;
// In general .write is required to avoid attempting to destruct
// the (uninitialized) previous contents of `ptr`, though for this
// simple example `*ptr = 5` would have worked as well.
ptr.write(5);
let x = Box::from_raw(ptr);
}
Sourcepub unsafe fn from_non_null(ptr: NonNull<T>) -> Box<T>
🔬This is a nightly-only experimental API. (box_vec_non_null
)
pub unsafe fn from_non_null(ptr: NonNull<T>) -> Box<T>
box_vec_non_null
)Constructs a box from a NonNull
pointer.
After calling this function, the NonNull
pointer is owned by
the resulting Box
. Specifically, the Box
destructor will call
the destructor of T
and free the allocated memory. For this
to be safe, the memory must have been allocated in accordance
with the memory layout used by Box
.
§Safety
This function is unsafe because improper use may lead to
memory problems. For example, a double-free may occur if the
function is called twice on the same NonNull
pointer.
The non-null pointer must point to a block of memory allocated by the global allocator.
The safety conditions are described in the memory layout section.
§Examples
Recreate a Box
which was previously converted to a NonNull
pointer using Box::into_non_null
:
#![feature(box_vec_non_null)]
let x = Box::new(5);
let non_null = Box::into_non_null(x);
let x = unsafe { Box::from_non_null(non_null) };
Manually create a Box
from scratch by using the global allocator:
#![feature(box_vec_non_null)]
use std::alloc::{alloc, Layout};
use std::ptr::NonNull;
unsafe {
let non_null = NonNull::new(alloc(Layout::new::<i32>()).cast::<i32>())
.expect("allocation failed");
// In general .write is required to avoid attempting to destruct
// the (uninitialized) previous contents of `non_null`.
non_null.write(5);
let x = Box::from_non_null(non_null);
}
Source§impl<T> Box<T>
impl<T> Box<T>
1.0.0 · Sourcepub fn new(x: T) -> Box<T>
pub fn new(x: T) -> Box<T>
Allocates memory on the heap and then places x
into it.
This doesn’t actually allocate if T
is zero-sized.
§Examples
let five = Box::new(5);
1.82.0 · Sourcepub fn new_uninit() -> Box<MaybeUninit<T>>
pub fn new_uninit() -> Box<MaybeUninit<T>>
Constructs a new box with uninitialized contents.
§Examples
let mut five = Box::<u32>::new_uninit();
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5)
Sourcepub fn new_zeroed() -> Box<MaybeUninit<T>>
🔬This is a nightly-only experimental API. (new_zeroed_alloc
)
pub fn new_zeroed() -> Box<MaybeUninit<T>>
new_zeroed_alloc
)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 · 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
)
pub fn try_new(x: T) -> Result<Box<T>, AllocError>
allocator_api
)Allocates memory on the heap then places x
into it,
returning an error if the allocation fails
This doesn’t actually allocate if T
is zero-sized.
§Examples
#![feature(allocator_api)]
let five = Box::try_new(5)?;
Sourcepub fn try_new_uninit() -> Result<Box<MaybeUninit<T>>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn try_new_uninit() -> Result<Box<MaybeUninit<T>>, AllocError>
allocator_api
)Constructs a new box with uninitialized contents on the heap, returning an error if the allocation fails
§Examples
#![feature(allocator_api)]
let mut five = Box::<u32>::try_new_uninit()?;
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5);
Sourcepub fn try_new_zeroed() -> Result<Box<MaybeUninit<T>>, AllocError>
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn try_new_zeroed() -> Result<Box<MaybeUninit<T>>, AllocError>
allocator_api
)Constructs a new Box
with uninitialized contents, with the memory
being filled with 0
bytes on the heap
See MaybeUninit::zeroed
for examples of correct and incorrect usage
of this method.
§Examples
#![feature(allocator_api)]
let zero = Box::<u32>::try_new_zeroed()?;
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0);
Source§impl<T, A> Box<T, A>
impl<T, A> Box<T, A>
Sourcepub const unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Box<T, A>
🔬This is a nightly-only experimental API. (allocator_api
)
pub const unsafe fn from_raw_in(raw: *mut T, alloc: A) -> Box<T, A>
allocator_api
)Constructs a box from a raw pointer in the given allocator.
After calling this function, the raw pointer is owned by the
resulting Box
. Specifically, the Box
destructor will call
the destructor of T
and free the allocated memory. For this
to be safe, the memory must have been allocated in accordance
with the memory layout used by Box
.
§Safety
This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.
The raw pointer must point to a block of memory allocated by alloc
.
§Examples
Recreate a Box
which was previously converted to a raw pointer
using Box::into_raw_with_allocator
:
#![feature(allocator_api)]
use std::alloc::System;
let x = Box::new_in(5, System);
let (ptr, alloc) = Box::into_raw_with_allocator(x);
let x = unsafe { Box::from_raw_in(ptr, alloc) };
Manually create a Box
from scratch by using the system allocator:
#![feature(allocator_api, slice_ptr_get)]
use std::alloc::{Allocator, Layout, System};
unsafe {
let ptr = System.allocate(Layout::new::<i32>())?.as_mut_ptr() as *mut i32;
// In general .write is required to avoid attempting to destruct
// the (uninitialized) previous contents of `ptr`, though for this
// simple example `*ptr = 5` would have worked as well.
ptr.write(5);
let x = Box::from_raw_in(ptr, System);
}
Sourcepub const unsafe fn from_non_null_in(raw: NonNull<T>, alloc: A) -> Box<T, A>
🔬This is a nightly-only experimental API. (allocator_api
)
pub const unsafe fn from_non_null_in(raw: NonNull<T>, alloc: A) -> Box<T, A>
allocator_api
)Constructs a box from a NonNull
pointer in the given allocator.
After calling this function, the NonNull
pointer is owned by
the resulting Box
. Specifically, the Box
destructor will call
the destructor of T
and free the allocated memory. For this
to be safe, the memory must have been allocated in accordance
with the memory layout used by Box
.
§Safety
This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.
The non-null pointer must point to a block of memory allocated by alloc
.
§Examples
Recreate a Box
which was previously converted to a NonNull
pointer
using Box::into_non_null_with_allocator
:
#![feature(allocator_api, box_vec_non_null)]
use std::alloc::System;
let x = Box::new_in(5, System);
let (non_null, alloc) = Box::into_non_null_with_allocator(x);
let x = unsafe { Box::from_non_null_in(non_null, alloc) };
Manually create a Box
from scratch by using the system allocator:
#![feature(allocator_api, box_vec_non_null, slice_ptr_get)]
use std::alloc::{Allocator, Layout, System};
unsafe {
let non_null = System.allocate(Layout::new::<i32>())?.cast::<i32>();
// In general .write is required to avoid attempting to destruct
// the (uninitialized) previous contents of `non_null`.
non_null.write(5);
let x = Box::from_non_null_in(non_null, System);
}
1.4.0 · 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) };
Manual cleanup by explicitly running the destructor and deallocating the memory:
use std::alloc::{dealloc, Layout};
use std::ptr;
let x = Box::new(String::from("Hello"));
let ptr = Box::into_raw(x);
unsafe {
ptr::drop_in_place(ptr);
dealloc(ptr as *mut u8, Layout::new::<String>());
}
Note: This is equivalent to the following:
let x = Box::new(String::from("Hello"));
let ptr = Box::into_raw(x);
unsafe {
drop(Box::from_raw(ptr));
}
Sourcepub fn into_non_null(b: Box<T, A>) -> NonNull<T>
🔬This is a nightly-only experimental API. (box_vec_non_null
)
pub fn into_non_null(b: Box<T, A>) -> NonNull<T>
box_vec_non_null
)Consumes the Box
, returning a wrapped NonNull
pointer.
The pointer will be properly aligned.
After calling this function, the caller is responsible for the
memory previously managed by the Box
. In particular, the
caller should properly destroy T
and release the memory, taking
into account the memory layout used by Box
. The easiest way to
do this is to convert the NonNull
pointer back into a Box
with the
Box::from_non_null
function, allowing the Box
destructor to
perform the cleanup.
Note: this is an associated function, which means that you have
to call it as Box::into_non_null(b)
instead of b.into_non_null()
.
This is so that there is no conflict with a method on the inner type.
§Examples
Converting the NonNull
pointer back into a Box
with Box::from_non_null
for automatic cleanup:
#![feature(box_vec_non_null)]
let x = Box::new(String::from("Hello"));
let non_null = Box::into_non_null(x);
let x = unsafe { Box::from_non_null(non_null) };
Manual cleanup by explicitly running the destructor and deallocating the memory:
#![feature(box_vec_non_null)]
use std::alloc::{dealloc, Layout};
let x = Box::new(String::from("Hello"));
let non_null = Box::into_non_null(x);
unsafe {
non_null.drop_in_place();
dealloc(non_null.as_ptr().cast::<u8>(), Layout::new::<String>());
}
Note: This is equivalent to the following:
#![feature(box_vec_non_null)]
let x = Box::new(String::from("Hello"));
let non_null = Box::into_non_null(x);
unsafe {
drop(Box::from_non_null(non_null));
}
Sourcepub fn into_raw_with_allocator(b: Box<T, A>) -> (*mut T, A)
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn into_raw_with_allocator(b: Box<T, A>) -> (*mut T, A)
allocator_api
)Consumes the Box
, returning a wrapped raw pointer and the allocator.
The pointer will be properly aligned and non-null.
After calling this function, the caller is responsible for the
memory previously managed by the Box
. In particular, the
caller should properly destroy T
and release the memory, taking
into account the memory layout used by Box
. The easiest way to
do this is to convert the raw pointer back into a Box
with the
Box::from_raw_in
function, allowing the Box
destructor to perform
the cleanup.
Note: this is an associated function, which means that you have
to call it as Box::into_raw_with_allocator(b)
instead of b.into_raw_with_allocator()
. This
is so that there is no conflict with a method on the inner type.
§Examples
Converting the raw pointer back into a Box
with Box::from_raw_in
for automatic cleanup:
#![feature(allocator_api)]
use std::alloc::System;
let x = Box::new_in(String::from("Hello"), System);
let (ptr, alloc) = Box::into_raw_with_allocator(x);
let x = unsafe { Box::from_raw_in(ptr, alloc) };
Manual cleanup by explicitly running the destructor and deallocating the memory:
#![feature(allocator_api)]
use std::alloc::{Allocator, Layout, System};
use std::ptr::{self, NonNull};
let x = Box::new_in(String::from("Hello"), System);
let (ptr, alloc) = Box::into_raw_with_allocator(x);
unsafe {
ptr::drop_in_place(ptr);
let non_null = NonNull::new_unchecked(ptr);
alloc.deallocate(non_null.cast(), Layout::new::<String>());
}
Sourcepub fn into_non_null_with_allocator(b: Box<T, A>) -> (NonNull<T>, A)
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn into_non_null_with_allocator(b: Box<T, A>) -> (NonNull<T>, A)
allocator_api
)Consumes the Box
, returning a wrapped NonNull
pointer and the allocator.
The pointer will be properly aligned.
After calling this function, the caller is responsible for the
memory previously managed by the Box
. In particular, the
caller should properly destroy T
and release the memory, taking
into account the memory layout used by Box
. The easiest way to
do this is to convert the NonNull
pointer back into a Box
with the
Box::from_non_null_in
function, allowing the Box
destructor to
perform the cleanup.
Note: this is an associated function, which means that you have
to call it as Box::into_non_null_with_allocator(b)
instead of
b.into_non_null_with_allocator()
. This is so that there is no
conflict with a method on the inner type.
§Examples
Converting the NonNull
pointer back into a Box
with
Box::from_non_null_in
for automatic cleanup:
#![feature(allocator_api, box_vec_non_null)]
use std::alloc::System;
let x = Box::new_in(String::from("Hello"), System);
let (non_null, alloc) = Box::into_non_null_with_allocator(x);
let x = unsafe { Box::from_non_null_in(non_null, alloc) };
Manual cleanup by explicitly running the destructor and deallocating the memory:
#![feature(allocator_api, box_vec_non_null)]
use std::alloc::{Allocator, Layout, System};
let x = Box::new_in(String::from("Hello"), System);
let (non_null, alloc) = Box::into_non_null_with_allocator(x);
unsafe {
non_null.drop_in_place();
alloc.deallocate(non_null.cast::<u8>(), Layout::new::<String>());
}
Sourcepub fn as_mut_ptr(b: &mut Box<T, A>) -> *mut T
🔬This is a nightly-only experimental API. (box_as_ptr
)
pub fn as_mut_ptr(b: &mut Box<T, A>) -> *mut T
box_as_ptr
)Returns a raw mutable pointer to the Box
’s contents.
The caller must ensure that the Box
outlives the pointer this
function returns, or else it will end up dangling.
This method guarantees that for the purpose of the aliasing model, this method
does not materialize a reference to the underlying memory, and thus the returned pointer
will remain valid when mixed with other calls to as_ptr
and as_mut_ptr
.
Note that calling other methods that materialize references to the memory
may still invalidate this pointer.
See the example below for how this guarantee can be used.
§Examples
Due to the aliasing guarantee, the following code is legal:
#![feature(box_as_ptr)]
unsafe {
let mut b = Box::new(0);
let ptr1 = Box::as_mut_ptr(&mut b);
ptr1.write(1);
let ptr2 = Box::as_mut_ptr(&mut b);
ptr2.write(2);
// Notably, the write to `ptr2` did *not* invalidate `ptr1`:
ptr1.write(3);
}
Sourcepub fn as_ptr(b: &Box<T, A>) -> *const T
🔬This is a nightly-only experimental API. (box_as_ptr
)
pub fn as_ptr(b: &Box<T, A>) -> *const T
box_as_ptr
)Returns a raw pointer to the Box
’s contents.
The caller must ensure that the Box
outlives the pointer this
function returns, or else it will end up dangling.
The caller must also ensure that the memory the pointer (non-transitively) points to
is never written to (except inside an UnsafeCell
) using this pointer or any pointer
derived from it. If you need to mutate the contents of the Box
, use as_mut_ptr
.
This method guarantees that for the purpose of the aliasing model, this method
does not materialize a reference to the underlying memory, and thus the returned pointer
will remain valid when mixed with other calls to as_ptr
and as_mut_ptr
.
Note that calling other methods that materialize mutable references to the memory,
as well as writing to this memory, may still invalidate this pointer.
See the example below for how this guarantee can be used.
§Examples
Due to the aliasing guarantee, the following code is legal:
#![feature(box_as_ptr)]
unsafe {
let mut v = Box::new(0);
let ptr1 = Box::as_ptr(&v);
let ptr2 = Box::as_mut_ptr(&mut v);
let _val = ptr2.read();
// No write to this memory has happened yet, so `ptr1` is still valid.
let _val = ptr1.read();
// However, once we do a write...
ptr2.write(1);
// ... `ptr1` is no longer valid.
// This would be UB: let _val = ptr1.read();
}
Sourcepub const fn allocator(b: &Box<T, A>) -> &A
🔬This is a nightly-only experimental API. (allocator_api
)
pub const fn allocator(b: &Box<T, A>) -> &A
allocator_api
)Returns a reference to the underlying allocator.
Note: this is an associated function, which means that you have
to call it as Box::allocator(&b)
instead of b.allocator()
. This
is so that there is no conflict with a method on the inner type.
1.26.0 · 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);
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) · 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.
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);
Source§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
)
pub fn new_in(x: T, alloc: A) -> Box<T, A>where
A: Allocator,
allocator_api
)Allocates memory in the given allocator then places x
into it.
This doesn’t actually allocate if T
is zero-sized.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let five = Box::new_in(5, System);
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
)
pub fn try_new_in(x: T, alloc: A) -> Result<Box<T, A>, AllocError>where
A: Allocator,
allocator_api
)Allocates memory in the given allocator then places x
into it,
returning an error if the allocation fails
This doesn’t actually allocate if T
is zero-sized.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let five = Box::try_new_in(5, System)?;
Sourcepub fn new_uninit_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn new_uninit_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
allocator_api
)Constructs a new box with uninitialized contents in the provided allocator.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let mut five = Box::<u32, _>::new_uninit_in(System);
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5)
Sourcepub 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
)
pub fn try_new_uninit_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where
A: Allocator,
allocator_api
)Constructs a new box with uninitialized contents in the provided allocator, returning an error if the allocation fails
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
let five = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);
five.assume_init()
};
assert_eq!(*five, 5);
Sourcepub fn new_zeroed_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn new_zeroed_in(alloc: A) -> Box<MaybeUninit<T>, A>where
A: Allocator,
allocator_api
)Constructs a new Box
with uninitialized contents, with the memory
being filled with 0
bytes in the provided allocator.
See MaybeUninit::zeroed
for examples of correct and incorrect usage
of this method.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let zero = Box::<u32, _>::new_zeroed_in(System);
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0)
Sourcepub 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
)
pub fn try_new_zeroed_in(alloc: A) -> Result<Box<MaybeUninit<T>, A>, AllocError>where
A: Allocator,
allocator_api
)Constructs a new Box
with uninitialized contents, with the memory
being filled with 0
bytes in the provided allocator,
returning an error if the allocation fails,
See MaybeUninit::zeroed
for examples of correct and incorrect usage
of this method.
§Examples
#![feature(allocator_api)]
use std::alloc::System;
let zero = Box::<u32, _>::try_new_zeroed_in(System)?;
let zero = unsafe { zero.assume_init() };
assert_eq!(*zero, 0);
Sourcepub fn pin_in(x: T, alloc: A) -> Pin<Box<T, A>>where
A: 'static + Allocator,
🔬This is a nightly-only experimental API. (allocator_api
)
pub fn pin_in(x: T, alloc: A) -> Pin<Box<T, A>>where
A: 'static + Allocator,
allocator_api
)Constructs a new Pin<Box<T, A>>
. If T
does not implement Unpin
, then
x
will be pinned in memory and unable to be moved.
Constructing and pinning of the Box
can also be done in two steps: Box::pin_in(x, alloc)
does the same as Box::into_pin(Box::new_in(x, alloc))
. Consider using
into_pin
if you already have a Box<T, A>
, or if you want to
construct a (pinned) Box
in a different way than with Box::new_in
.
Sourcepub fn into_boxed_slice(boxed: Box<T, A>) -> Box<[T], A>
🔬This is a nightly-only experimental API. (box_into_boxed_slice
)
pub fn into_boxed_slice(boxed: Box<T, A>) -> Box<[T], A>
box_into_boxed_slice
)Converts a Box<T>
into a Box<[T]>
This conversion does not allocate on the heap and happens in place.
Sourcepub fn into_inner(boxed: Box<T, A>) -> T
🔬This is a nightly-only experimental API. (box_into_inner
)
pub fn into_inner(boxed: Box<T, A>) -> T
box_into_inner
)Consumes the Box
, returning the wrapped value.
§Examples
#![feature(box_into_inner)]
let c = Box::new(5);
assert_eq!(Box::into_inner(c), 5);
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1.64.0 · Source§impl<T> AsFd for Box<T>
impl<T> AsFd for Box<T>
Source§fn as_fd(&self) -> BorrowedFd<'_>
fn as_fd(&self) -> BorrowedFd<'_>
1.85.0 · Source§impl<Args, F, A> AsyncFn<Args> for Box<F, A>
impl<Args, F, A> AsyncFn<Args> for Box<F, A>
Source§extern "rust-call" fn async_call(
&self,
args: Args,
) -> <Box<F, A> as AsyncFnMut<Args>>::CallRefFuture<'_>
extern "rust-call" fn async_call( &self, args: Args, ) -> <Box<F, A> as AsyncFnMut<Args>>::CallRefFuture<'_>
async_fn_traits
)AsyncFn
, returning a future which may borrow from the called closure.1.85.0 · Source§impl<Args, F, A> AsyncFnMut<Args> for Box<F, A>
impl<Args, F, A> AsyncFnMut<Args> for Box<F, A>
Source§type CallRefFuture<'a> = <F as AsyncFnMut<Args>>::CallRefFuture<'a>
where
Box<F, A>: 'a
type CallRefFuture<'a> = <F as AsyncFnMut<Args>>::CallRefFuture<'a> where Box<F, A>: 'a
async_fn_traits
)AsyncFnMut::async_call_mut
and AsyncFn::async_call
.Source§extern "rust-call" fn async_call_mut(
&mut self,
args: Args,
) -> <Box<F, A> as AsyncFnMut<Args>>::CallRefFuture<'_>
extern "rust-call" fn async_call_mut( &mut self, args: Args, ) -> <Box<F, A> as AsyncFnMut<Args>>::CallRefFuture<'_>
async_fn_traits
)AsyncFnMut
, returning a future which may borrow from the called closure.1.85.0 · Source§impl<Args, F, A> AsyncFnOnce<Args> for Box<F, A>
impl<Args, F, A> AsyncFnOnce<Args> for Box<F, A>
Source§type Output = <F as AsyncFnOnce<Args>>::Output
type Output = <F as AsyncFnOnce<Args>>::Output
async_fn_traits
)Source§type CallOnceFuture = <F as AsyncFnOnce<Args>>::CallOnceFuture
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async_fn_traits
)AsyncFnOnce::async_call_once
.Source§extern "rust-call" fn async_call_once(
self,
args: Args,
) -> <Box<F, A> as AsyncFnOnce<Args>>::CallOnceFuture
extern "rust-call" fn async_call_once( self, args: Args, ) -> <Box<F, A> as AsyncFnOnce<Args>>::CallOnceFuture
async_fn_traits
)AsyncFnOnce
, returning a future which may move out of the called closure.Source§impl<S> AsyncIterator for Box<S>
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Source§type Item = <S as AsyncIterator>::Item
type Item = <S as AsyncIterator>::Item
async_iterator
)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
)None
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Source§fn borrow_mut(&mut self) -> &mut T
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Source§fn fill_buf(&mut self) -> Result<&[u8], Error>
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Source§fn consume(&mut self, amt: usize)
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. Read moreSource§fn read_line(&mut self, buf: &mut String) -> Result<usize, Error>
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impl<T, A> Clone for Box<T, A>
Source§fn clone(&self) -> Box<T, A>
fn clone(&self) -> Box<T, A>
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§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);
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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);
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impl<G, R, A> Coroutine<R> for Box<G, A>
Source§type Yield = <G as Coroutine<R>>::Yield
type Yield = <G as Coroutine<R>>::Yield
coroutine_trait
)1.0.0 · 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>
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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
)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()
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E: Error,
impl<E> Error for Box<E>where
E: Error,
Source§fn description(&self) -> &str
fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
1.0.0 · Source§impl<I, A> ExactSizeIterator for Box<I, A>
impl<I, A> ExactSizeIterator for Box<I, A>
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
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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
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fn write_isize(&mut self, i: isize)
isize
into this hasher.Source§fn write_length_prefix(&mut self, len: usize)
fn write_length_prefix(&mut self, len: usize)
hasher_prefixfree_extras
)1.0.0 · 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>
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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
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fn next_chunk<const N: usize>(
&mut self,
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
Self: Sized,
iter_next_chunk
)N
values. Read more1.0.0 · Source§fn count(self) -> usizewhere
Self: Sized,
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Self: Sized,
Source§fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>
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iter_advance_by
)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,
1.0.0 · Source§fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter>
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Source§fn intersperse(self, separator: Self::Item) -> Intersperse<Self>
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iter_intersperse
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fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>
iter_intersperse
)separator
between adjacent items of the original iterator. Read more1.0.0 · Source§fn map<B, F>(self, f: F) -> Map<Self, F>
fn map<B, F>(self, f: F) -> Map<Self, F>
1.0.0 · Source§fn filter<P>(self, predicate: P) -> Filter<Self, P>
fn filter<P>(self, predicate: P) -> Filter<Self, P>
1.0.0 · Source§fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
1.0.0 · Source§fn enumerate(self) -> Enumerate<Self>where
Self: Sized,
fn enumerate(self) -> Enumerate<Self>where
Self: Sized,
1.0.0 · Source§fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
1.0.0 · 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>
1.0.0 · Source§fn skip(self, n: usize) -> Skip<Self>where
Self: Sized,
fn skip(self, n: usize) -> Skip<Self>where
Self: Sized,
n
elements. Read more1.0.0 · Source§fn take(self, n: usize) -> Take<Self>where
Self: Sized,
fn take(self, n: usize) -> Take<Self>where
Self: Sized,
n
elements, or fewer
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fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
1.29.0 · Source§fn flatten(self) -> Flatten<Self>
fn flatten(self) -> Flatten<Self>
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
)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 more1.0.0 · Source§fn inspect<F>(self, f: F) -> Inspect<Self, F>
fn inspect<F>(self, f: F) -> Inspect<Self, F>
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&mut self,
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)Source§fn collect_into<E>(self, collection: &mut E) -> &mut E
fn collect_into<E>(self, collection: &mut E) -> &mut E
iter_collect_into
)1.0.0 · Source§fn partition<B, F>(self, f: F) -> (B, B)
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)true
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. 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
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&mut self,
f: impl FnMut(Self::Item, Self::Item) -> R,
) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
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)1.0.0 · Source§fn all<F>(&mut self, f: F) -> bool
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Source§fn try_find<R>(
&mut self,
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) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
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)1.0.0 · Source§fn position<P>(&mut self, predicate: P) -> Option<usize>
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fn max(self) -> Option<Self::Item>
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fn min(self) -> Option<Self::Item>
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fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>
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fn min_by<F>(self, compare: F) -> Option<Self::Item>
1.0.0 · Source§fn rev(self) -> Rev<Self>where
Self: Sized + DoubleEndedIterator,
fn rev(self) -> Rev<Self>where
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1.0.0 · Source§fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
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Source§fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>where
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fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>where
Self: Sized,
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)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
)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
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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>,
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)Iterator
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)1.5.0 · Source§fn lt<I>(self, other: I) -> bool
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Iterator
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Iterator
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Iterator
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Iterator
are lexicographically
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impl<T, A> Ord for Box<T, A>
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impl<T, A> PartialOrd for Box<T, A>
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Source§fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error>
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)Source§fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>
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fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>
buf
. Read moreSource§fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>
read_buf
)cursor
. Read more1.0.0 · Source§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Read
. Read more1.0.0 · Source§impl<S> Seek for Box<S>
impl<S> Seek for Box<S>
Source§fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error>
fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error>
Source§fn stream_position(&mut self) -> Result<u64, Error>
fn stream_position(&mut self) -> Result<u64, Error>
1.55.0 · Source§fn rewind(&mut self) -> Result<(), Error>
fn rewind(&mut self) -> Result<(), Error>
1.0.0 · Source§impl<W> Write for Box<W>
impl<W> Write for Box<W>
Source§fn write(&mut self, buf: &[u8]) -> Result<usize, Error>
fn write(&mut self, buf: &[u8]) -> Result<usize, Error>
Source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
)