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Unrolled build for rust-lang#136976
Rollup merge of rust-lang#136976 - jedbrown:jed/doc-boxed-deferred-init, r=tgross35 alloc boxed: docs: use MaybeUninit::write instead of as_mut_ptr In the deferred initialization pattern, the docs were needlessly going through `as_mut_ptr().write()` to initialize, which is unnecessary use of a pointer, needs to be inside an `unsafe` block, and may weaken alias analysis.
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‎library/alloc/src/boxed.rs

+44-84
Original file line numberDiff line numberDiff line change
@@ -280,13 +280,9 @@ impl<T> Box<T> {
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///
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/// ```
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/// let mut five = Box::<u32>::new_uninit();
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///
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/// let five = unsafe {
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/// // Deferred initialization:
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/// five.as_mut_ptr().write(5);
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///
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/// five.assume_init()
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/// };
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// assert_eq!(*five, 5)
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/// ```
@@ -367,13 +363,9 @@ impl<T> Box<T> {
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/// #![feature(allocator_api)]
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///
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/// let mut five = Box::<u32>::try_new_uninit()?;
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///
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/// let five = unsafe {
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/// // Deferred initialization:
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/// five.as_mut_ptr().write(5);
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///
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/// five.assume_init()
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/// };
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// assert_eq!(*five, 5);
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/// # Ok::<(), std::alloc::AllocError>(())
@@ -435,10 +427,8 @@ impl<T, A: Allocator> Box<T, A> {
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A: Allocator,
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{
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let mut boxed = Self::new_uninit_in(alloc);
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unsafe {
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boxed.as_mut_ptr().write(x);
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boxed.assume_init()
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}
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boxed.write(x);
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unsafe { boxed.assume_init() }
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}
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/// Allocates memory in the given allocator then places `x` into it,
@@ -463,10 +453,8 @@ impl<T, A: Allocator> Box<T, A> {
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A: Allocator,
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{
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let mut boxed = Self::try_new_uninit_in(alloc)?;
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unsafe {
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boxed.as_mut_ptr().write(x);
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Ok(boxed.assume_init())
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}
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boxed.write(x);
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unsafe { Ok(boxed.assume_init()) }
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}
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/// Constructs a new box with uninitialized contents in the provided allocator.
@@ -479,13 +467,9 @@ impl<T, A: Allocator> Box<T, A> {
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/// use std::alloc::System;
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///
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/// let mut five = Box::<u32, _>::new_uninit_in(System);
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///
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/// let five = unsafe {
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/// // Deferred initialization:
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/// five.as_mut_ptr().write(5);
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///
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/// five.assume_init()
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/// };
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// assert_eq!(*five, 5)
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/// ```
@@ -517,13 +501,9 @@ impl<T, A: Allocator> Box<T, A> {
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/// use std::alloc::System;
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///
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/// let mut five = Box::<u32, _>::try_new_uninit_in(System)?;
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///
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/// let five = unsafe {
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/// // Deferred initialization:
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/// five.as_mut_ptr().write(5);
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///
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/// five.assume_init()
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/// };
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/// // Deferred initialization:
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/// five.write(5);
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/// let five = unsafe { five.assume_init() };
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///
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/// assert_eq!(*five, 5);
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/// # Ok::<(), std::alloc::AllocError>(())
@@ -669,15 +649,11 @@ impl<T> Box<[T]> {
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///
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/// ```
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/// let mut values = Box::<[u32]>::new_uninit_slice(3);
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///
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/// let values = unsafe {
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/// // Deferred initialization:
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/// values[0].as_mut_ptr().write(1);
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/// values[1].as_mut_ptr().write(2);
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/// values[2].as_mut_ptr().write(3);
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///
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/// values.assume_init()
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/// };
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/// // Deferred initialization:
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/// values[0].write(1);
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/// values[1].write(2);
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/// values[2].write(3);
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/// let values = unsafe {values.assume_init() };
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///
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/// assert_eq!(*values, [1, 2, 3])
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/// ```
@@ -722,13 +698,11 @@ impl<T> Box<[T]> {
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/// #![feature(allocator_api)]
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///
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/// let mut values = Box::<[u32]>::try_new_uninit_slice(3)?;
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/// let values = unsafe {
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/// // Deferred initialization:
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/// values[0].as_mut_ptr().write(1);
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/// values[1].as_mut_ptr().write(2);
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/// values[2].as_mut_ptr().write(3);
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/// values.assume_init()
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/// };
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/// // Deferred initialization:
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/// values[0].write(1);
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/// values[1].write(2);
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/// values[2].write(3);
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/// let values = unsafe { values.assume_init() };
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///
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/// assert_eq!(*values, [1, 2, 3]);
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/// # Ok::<(), std::alloc::AllocError>(())
@@ -814,15 +788,11 @@ impl<T, A: Allocator> Box<[T], A> {
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/// use std::alloc::System;
815789
///
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/// let mut values = Box::<[u32], _>::new_uninit_slice_in(3, System);
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///
818-
/// let values = unsafe {
819-
/// // Deferred initialization:
820-
/// values[0].as_mut_ptr().write(1);
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/// values[1].as_mut_ptr().write(2);
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/// values[2].as_mut_ptr().write(3);
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///
824-
/// values.assume_init()
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/// };
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/// // Deferred initialization:
792+
/// values[0].write(1);
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/// values[1].write(2);
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/// values[2].write(3);
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/// let values = unsafe { values.assume_init() };
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///
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/// assert_eq!(*values, [1, 2, 3])
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/// ```
@@ -873,13 +843,11 @@ impl<T, A: Allocator> Box<[T], A> {
873843
/// use std::alloc::System;
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///
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/// let mut values = Box::<[u32], _>::try_new_uninit_slice_in(3, System)?;
876-
/// let values = unsafe {
877-
/// // Deferred initialization:
878-
/// values[0].as_mut_ptr().write(1);
879-
/// values[1].as_mut_ptr().write(2);
880-
/// values[2].as_mut_ptr().write(3);
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/// values.assume_init()
882-
/// };
846+
/// // Deferred initialization:
847+
/// values[0].write(1);
848+
/// values[1].write(2);
849+
/// values[2].write(3);
850+
/// let values = unsafe { values.assume_init() };
883851
///
884852
/// assert_eq!(*values, [1, 2, 3]);
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/// # Ok::<(), std::alloc::AllocError>(())
@@ -959,13 +927,9 @@ impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
959927
///
960928
/// ```
961929
/// let mut five = Box::<u32>::new_uninit();
962-
///
963-
/// let five: Box<u32> = unsafe {
964-
/// // Deferred initialization:
965-
/// five.as_mut_ptr().write(5);
966-
///
967-
/// five.assume_init()
968-
/// };
930+
/// // Deferred initialization:
931+
/// five.write(5);
932+
/// let five: Box<u32> = unsafe { five.assume_init() };
969933
///
970934
/// assert_eq!(*five, 5)
971935
/// ```
@@ -1030,15 +994,11 @@ impl<T, A: Allocator> Box<[mem::MaybeUninit<T>], A> {
1030994
///
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/// ```
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/// let mut values = Box::<[u32]>::new_uninit_slice(3);
1033-
///
1034-
/// let values = unsafe {
1035-
/// // Deferred initialization:
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/// values[0].as_mut_ptr().write(1);
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/// values[1].as_mut_ptr().write(2);
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/// values[2].as_mut_ptr().write(3);
1039-
///
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/// values.assume_init()
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/// };
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/// // Deferred initialization:
998+
/// values[0].write(1);
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/// values[1].write(2);
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/// values[2].write(3);
1001+
/// let values = unsafe { values.assume_init() };
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///
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/// assert_eq!(*values, [1, 2, 3])
10441004
/// ```

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