From 2f27236745fab41c73450cdb31cdf9d0db502dda Mon Sep 17 00:00:00 2001
From: Jed Brown <jed@jedbrown.org>
Date: Thu, 13 Feb 2025 09:13:33 -0700
Subject: [PATCH] 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.
---
library/alloc/src/boxed.rs | 128 +++++++++++++------------------------
1 file changed, 44 insertions(+), 84 deletions(-)
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 8b38e6fc259af..60e46dc7a09cf 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -280,13 +280,9 @@ impl<T> Box<T> {
///
/// ```
/// let mut five = Box::<u32>::new_uninit();
- ///
- /// let five = unsafe {
- /// // Deferred initialization:
- /// five.as_mut_ptr().write(5);
- ///
- /// five.assume_init()
- /// };
+ /// // Deferred initialization:
+ /// five.write(5);
+ /// let five = unsafe { five.assume_init() };
///
/// assert_eq!(*five, 5)
/// ```
@@ -367,13 +363,9 @@ impl<T> Box<T> {
/// #![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()
- /// };
+ /// // Deferred initialization:
+ /// five.write(5);
+ /// let five = unsafe { five.assume_init() };
///
/// assert_eq!(*five, 5);
/// # Ok::<(), std::alloc::AllocError>(())
@@ -435,10 +427,8 @@ impl<T, A: Allocator> Box<T, A> {
A: Allocator,
{
let mut boxed = Self::new_uninit_in(alloc);
- unsafe {
- boxed.as_mut_ptr().write(x);
- boxed.assume_init()
- }
+ boxed.write(x);
+ unsafe { boxed.assume_init() }
}
/// Allocates memory in the given allocator then places `x` into it,
@@ -463,10 +453,8 @@ impl<T, A: Allocator> Box<T, A> {
A: Allocator,
{
let mut boxed = Self::try_new_uninit_in(alloc)?;
- unsafe {
- boxed.as_mut_ptr().write(x);
- Ok(boxed.assume_init())
- }
+ boxed.write(x);
+ unsafe { Ok(boxed.assume_init()) }
}
/// Constructs a new box with uninitialized contents in the provided allocator.
@@ -479,13 +467,9 @@ impl<T, A: Allocator> Box<T, A> {
/// 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()
- /// };
+ /// // Deferred initialization:
+ /// five.write(5);
+ /// let five = unsafe { five.assume_init() };
///
/// assert_eq!(*five, 5)
/// ```
@@ -517,13 +501,9 @@ impl<T, A: Allocator> Box<T, A> {
/// 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()
- /// };
+ /// // Deferred initialization:
+ /// five.write(5);
+ /// let five = unsafe { five.assume_init() };
///
/// assert_eq!(*five, 5);
/// # Ok::<(), std::alloc::AllocError>(())
@@ -669,15 +649,11 @@ impl<T> Box<[T]> {
///
/// ```
/// 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()
- /// };
+ /// // Deferred initialization:
+ /// values[0].write(1);
+ /// values[1].write(2);
+ /// values[2].write(3);
+ /// let values = unsafe {values.assume_init() };
///
/// assert_eq!(*values, [1, 2, 3])
/// ```
@@ -722,13 +698,11 @@ impl<T> Box<[T]> {
/// #![feature(allocator_api)]
///
/// 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()
- /// };
+ /// // Deferred initialization:
+ /// values[0].write(1);
+ /// values[1].write(2);
+ /// values[2].write(3);
+ /// let values = unsafe { values.assume_init() };
///
/// assert_eq!(*values, [1, 2, 3]);
/// # Ok::<(), std::alloc::AllocError>(())
@@ -814,15 +788,11 @@ impl<T, A: Allocator> Box<[T], A> {
/// 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()
- /// };
+ /// // Deferred initialization:
+ /// values[0].write(1);
+ /// values[1].write(2);
+ /// values[2].write(3);
+ /// let values = unsafe { values.assume_init() };
///
/// assert_eq!(*values, [1, 2, 3])
/// ```
@@ -873,13 +843,11 @@ impl<T, A: Allocator> Box<[T], A> {
/// use std::alloc::System;
///
/// let mut values = Box::<[u32], _>::try_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()
- /// };
+ /// // Deferred initialization:
+ /// values[0].write(1);
+ /// values[1].write(2);
+ /// values[2].write(3);
+ /// let values = unsafe { values.assume_init() };
///
/// assert_eq!(*values, [1, 2, 3]);
/// # Ok::<(), std::alloc::AllocError>(())
@@ -959,13 +927,9 @@ impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
///
/// ```
/// let mut five = Box::<u32>::new_uninit();
- ///
- /// let five: Box<u32> = unsafe {
- /// // Deferred initialization:
- /// five.as_mut_ptr().write(5);
- ///
- /// five.assume_init()
- /// };
+ /// // Deferred initialization:
+ /// five.write(5);
+ /// let five: Box<u32> = unsafe { five.assume_init() };
///
/// assert_eq!(*five, 5)
/// ```
@@ -1030,15 +994,11 @@ impl<T, A: Allocator> Box<[mem::MaybeUninit<T>], A> {
///
/// ```
/// 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()
- /// };
+ /// // Deferred initialization:
+ /// values[0].write(1);
+ /// values[1].write(2);
+ /// values[2].write(3);
+ /// let values = unsafe { values.assume_init() };
///
/// assert_eq!(*values, [1, 2, 3])
/// ```