1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625
#![doc = include_str!("../README.md")]
#![no_std]
#![cfg_attr(docsrs, feature(doc_auto_cfg))]
#![allow(unsafe_code)]
#![doc(
html_logo_url = "https://bevyengine.org/assets/icon.png",
html_favicon_url = "https://bevyengine.org/assets/icon.png"
)]
use core::fmt::{self, Formatter, Pointer};
use core::{
cell::UnsafeCell, marker::PhantomData, mem::ManuallyDrop, num::NonZeroUsize, ptr::NonNull,
};
/// Used as a type argument to [`Ptr`], [`PtrMut`] and [`OwningPtr`] to specify that the pointer is aligned.
#[derive(Copy, Clone)]
pub struct Aligned;
/// Used as a type argument to [`Ptr`], [`PtrMut`] and [`OwningPtr`] to specify that the pointer is not aligned.
#[derive(Copy, Clone)]
pub struct Unaligned;
/// Trait that is only implemented for [`Aligned`] and [`Unaligned`] to work around the lack of ability
/// to have const generics of an enum.
pub trait IsAligned: sealed::Sealed {}
impl IsAligned for Aligned {}
impl IsAligned for Unaligned {}
mod sealed {
pub trait Sealed {}
impl Sealed for super::Aligned {}
impl Sealed for super::Unaligned {}
}
/// A newtype around [`NonNull`] that only allows conversion to read-only borrows or pointers.
///
/// This type can be thought of as the `*const T` to [`NonNull<T>`]'s `*mut T`.
#[repr(transparent)]
pub struct ConstNonNull<T: ?Sized>(NonNull<T>);
impl<T: ?Sized> ConstNonNull<T> {
/// Creates a new `ConstNonNull` if `ptr` is non-null.
///
/// # Examples
///
/// ```
/// use bevy_ptr::ConstNonNull;
///
/// let x = 0u32;
/// let ptr = ConstNonNull::<u32>::new(&x as *const _).expect("ptr is null!");
///
/// if let Some(ptr) = ConstNonNull::<u32>::new(std::ptr::null()) {
/// unreachable!();
/// }
/// ```
pub fn new(ptr: *const T) -> Option<Self> {
NonNull::new(ptr.cast_mut()).map(Self)
}
/// Creates a new `ConstNonNull`.
///
/// # Safety
///
/// `ptr` must be non-null.
///
/// # Examples
///
/// ```
/// use bevy_ptr::ConstNonNull;
///
/// let x = 0u32;
/// let ptr = unsafe { ConstNonNull::new_unchecked(&x as *const _) };
/// ```
///
/// *Incorrect* usage of this function:
///
/// ```rust,no_run
/// use bevy_ptr::ConstNonNull;
///
/// // NEVER DO THAT!!! This is undefined behavior. ⚠️
/// let ptr = unsafe { ConstNonNull::<u32>::new_unchecked(std::ptr::null()) };
/// ```
pub const unsafe fn new_unchecked(ptr: *const T) -> Self {
// SAFETY: This function's safety invariants are identical to `NonNull::new_unchecked`
// The caller must satisfy all of them.
unsafe { Self(NonNull::new_unchecked(ptr.cast_mut())) }
}
/// Returns a shared reference to the value.
///
/// # Safety
///
/// When calling this method, you have to ensure that all of the following is true:
///
/// * The pointer must be properly aligned.
///
/// * It must be "dereferenceable" in the sense defined in [the module documentation].
///
/// * The pointer must point to an initialized instance of `T`.
///
/// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
/// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
/// In particular, while this reference exists, the memory the pointer points to must
/// not get mutated (except inside `UnsafeCell`).
///
/// This applies even if the result of this method is unused!
/// (The part about being initialized is not yet fully decided, but until
/// it is, the only safe approach is to ensure that they are indeed initialized.)
///
/// # Examples
///
/// ```
/// use bevy_ptr::ConstNonNull;
///
/// let mut x = 0u32;
/// let ptr = ConstNonNull::new(&mut x as *mut _).expect("ptr is null!");
///
/// let ref_x = unsafe { ptr.as_ref() };
/// println!("{ref_x}");
/// ```
///
/// [the module documentation]: core::ptr#safety
#[inline]
pub unsafe fn as_ref<'a>(&self) -> &'a T {
// SAFETY: This function's safety invariants are identical to `NonNull::as_ref`
// The caller must satisfy all of them.
unsafe { self.0.as_ref() }
}
}
impl<T: ?Sized> From<NonNull<T>> for ConstNonNull<T> {
fn from(value: NonNull<T>) -> ConstNonNull<T> {
ConstNonNull(value)
}
}
impl<'a, T: ?Sized> From<&'a T> for ConstNonNull<T> {
fn from(value: &'a T) -> ConstNonNull<T> {
ConstNonNull(NonNull::from(value))
}
}
impl<'a, T: ?Sized> From<&'a mut T> for ConstNonNull<T> {
fn from(value: &'a mut T) -> ConstNonNull<T> {
ConstNonNull(NonNull::from(value))
}
}
/// Type-erased borrow of some unknown type chosen when constructing this type.
///
/// This type tries to act "borrow-like" which means that:
/// - It should be considered immutable: its target must not be changed while this pointer is alive.
/// - It must always points to a valid value of whatever the pointee type is.
/// - The lifetime `'a` accurately represents how long the pointer is valid for.
/// - Must be sufficiently aligned for the unknown pointee type.
///
/// It may be helpful to think of this type as similar to `&'a dyn Any` but without
/// the metadata and able to point to data that does not correspond to a Rust type.
#[derive(Copy, Clone, Debug)]
#[repr(transparent)]
pub struct Ptr<'a, A: IsAligned = Aligned>(NonNull<u8>, PhantomData<(&'a u8, A)>);
/// Type-erased mutable borrow of some unknown type chosen when constructing this type.
///
/// This type tries to act "borrow-like" which means that:
/// - Pointer is considered exclusive and mutable. It cannot be cloned as this would lead to
/// aliased mutability.
/// - It must always points to a valid value of whatever the pointee type is.
/// - The lifetime `'a` accurately represents how long the pointer is valid for.
/// - Must be sufficiently aligned for the unknown pointee type.
///
/// It may be helpful to think of this type as similar to `&'a mut dyn Any` but without
/// the metadata and able to point to data that does not correspond to a Rust type.
#[derive(Debug)]
#[repr(transparent)]
pub struct PtrMut<'a, A: IsAligned = Aligned>(NonNull<u8>, PhantomData<(&'a mut u8, A)>);
/// Type-erased Box-like pointer to some unknown type chosen when constructing this type.
/// Conceptually represents ownership of whatever data is being pointed to and so is
/// responsible for calling its `Drop` impl. This pointer is _not_ responsible for freeing
/// the memory pointed to by this pointer as it may be pointing to an element in a `Vec` or
/// to a local in a function etc.
///
/// This type tries to act "borrow-like" like which means that:
/// - Pointer should be considered exclusive and mutable. It cannot be cloned as this would lead
/// to aliased mutability and potentially use after free bugs.
/// - It must always points to a valid value of whatever the pointee type is.
/// - The lifetime `'a` accurately represents how long the pointer is valid for.
/// - Must be sufficiently aligned for the unknown pointee type.
///
/// It may be helpful to think of this type as similar to `&'a mut ManuallyDrop<dyn Any>` but
/// without the metadata and able to point to data that does not correspond to a Rust type.
#[derive(Debug)]
#[repr(transparent)]
pub struct OwningPtr<'a, A: IsAligned = Aligned>(NonNull<u8>, PhantomData<(&'a mut u8, A)>);
macro_rules! impl_ptr {
($ptr:ident) => {
impl<'a> $ptr<'a, Aligned> {
/// Removes the alignment requirement of this pointer
pub fn to_unaligned(self) -> $ptr<'a, Unaligned> {
$ptr(self.0, PhantomData)
}
}
impl<'a, A: IsAligned> From<$ptr<'a, A>> for NonNull<u8> {
fn from(ptr: $ptr<'a, A>) -> Self {
ptr.0
}
}
impl<A: IsAligned> $ptr<'_, A> {
/// Calculates the offset from a pointer.
/// As the pointer is type-erased, there is no size information available. The provided
/// `count` parameter is in raw bytes.
///
/// *See also: [`ptr::offset`][ptr_offset]*
///
/// # Safety
/// - The offset cannot make the existing ptr null, or take it out of bounds for its allocation.
/// - If the `A` type parameter is [`Aligned`] then the offset must not make the resulting pointer
/// be unaligned for the pointee type.
/// - The value pointed by the resulting pointer must outlive the lifetime of this pointer.
///
/// [ptr_offset]: https://doc.rust-lang.org/std/primitive.pointer.html#method.offset
#[inline]
pub unsafe fn byte_offset(self, count: isize) -> Self {
Self(
// SAFETY: The caller upholds safety for `offset` and ensures the result is not null.
unsafe { NonNull::new_unchecked(self.as_ptr().offset(count)) },
PhantomData,
)
}
/// Calculates the offset from a pointer (convenience for `.offset(count as isize)`).
/// As the pointer is type-erased, there is no size information available. The provided
/// `count` parameter is in raw bytes.
///
/// *See also: [`ptr::add`][ptr_add]*
///
/// # Safety
/// - The offset cannot make the existing ptr null, or take it out of bounds for its allocation.
/// - If the `A` type parameter is [`Aligned`] then the offset must not make the resulting pointer
/// be unaligned for the pointee type.
/// - The value pointed by the resulting pointer must outlive the lifetime of this pointer.
///
/// [ptr_add]: https://doc.rust-lang.org/std/primitive.pointer.html#method.add
#[inline]
pub unsafe fn byte_add(self, count: usize) -> Self {
Self(
// SAFETY: The caller upholds safety for `add` and ensures the result is not null.
unsafe { NonNull::new_unchecked(self.as_ptr().add(count)) },
PhantomData,
)
}
}
impl<A: IsAligned> Pointer for $ptr<'_, A> {
#[inline]
fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
Pointer::fmt(&self.0, f)
}
}
};
}
impl_ptr!(Ptr);
impl_ptr!(PtrMut);
impl_ptr!(OwningPtr);
impl<'a, A: IsAligned> Ptr<'a, A> {
/// Creates a new instance from a raw pointer.
///
/// # Safety
/// - `inner` must point to valid value of whatever the pointee type is.
/// - If the `A` type parameter is [`Aligned`] then `inner` must be sufficiently aligned for the pointee type.
/// - `inner` must have correct provenance to allow reads of the pointee type.
/// - The lifetime `'a` must be constrained such that this [`Ptr`] will stay valid and nothing
/// can mutate the pointee while this [`Ptr`] is live except through an [`UnsafeCell`].
#[inline]
pub unsafe fn new(inner: NonNull<u8>) -> Self {
Self(inner, PhantomData)
}
/// Transforms this [`Ptr`] into an [`PtrMut`]
///
/// # Safety
/// Another [`PtrMut`] for the same [`Ptr`] must not be created until the first is dropped.
#[inline]
pub unsafe fn assert_unique(self) -> PtrMut<'a, A> {
PtrMut(self.0, PhantomData)
}
/// Transforms this [`Ptr<T>`] into a `&T` with the same lifetime
///
/// # Safety
/// - `T` must be the erased pointee type for this [`Ptr`].
/// - If the type parameter `A` is [`Unaligned`] then this pointer must be sufficiently aligned
/// for the pointee type `T`.
#[inline]
pub unsafe fn deref<T>(self) -> &'a T {
let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
// SAFETY: The caller ensures the pointee is of type `T` and the pointer can be dereferenced.
unsafe { &*ptr }
}
/// Gets the underlying pointer, erasing the associated lifetime.
///
/// If possible, it is strongly encouraged to use [`deref`](Self::deref) over this function,
/// as it retains the lifetime.
#[inline]
#[allow(clippy::wrong_self_convention)]
pub fn as_ptr(self) -> *mut u8 {
self.0.as_ptr()
}
}
impl<'a, T> From<&'a T> for Ptr<'a> {
#[inline]
fn from(val: &'a T) -> Self {
// SAFETY: The returned pointer has the same lifetime as the passed reference.
// Access is immutable.
unsafe { Self::new(NonNull::from(val).cast()) }
}
}
impl<'a, A: IsAligned> PtrMut<'a, A> {
/// Creates a new instance from a raw pointer.
///
/// # Safety
/// - `inner` must point to valid value of whatever the pointee type is.
/// - If the `A` type parameter is [`Aligned`] then `inner` must be sufficiently aligned for the pointee type.
/// - `inner` must have correct provenance to allow read and writes of the pointee type.
/// - The lifetime `'a` must be constrained such that this [`PtrMut`] will stay valid and nothing
/// else can read or mutate the pointee while this [`PtrMut`] is live.
#[inline]
pub unsafe fn new(inner: NonNull<u8>) -> Self {
Self(inner, PhantomData)
}
/// Transforms this [`PtrMut`] into an [`OwningPtr`]
///
/// # Safety
/// Must have right to drop or move out of [`PtrMut`].
#[inline]
pub unsafe fn promote(self) -> OwningPtr<'a, A> {
OwningPtr(self.0, PhantomData)
}
/// Transforms this [`PtrMut<T>`] into a `&mut T` with the same lifetime
///
/// # Safety
/// - `T` must be the erased pointee type for this [`PtrMut`].
/// - If the type parameter `A` is [`Unaligned`] then this pointer must be sufficiently aligned
/// for the pointee type `T`.
#[inline]
pub unsafe fn deref_mut<T>(self) -> &'a mut T {
let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
// SAFETY: The caller ensures the pointee is of type `T` and the pointer can be dereferenced.
unsafe { &mut *ptr }
}
/// Gets the underlying pointer, erasing the associated lifetime.
///
/// If possible, it is strongly encouraged to use [`deref_mut`](Self::deref_mut) over
/// this function, as it retains the lifetime.
#[inline]
#[allow(clippy::wrong_self_convention)]
pub fn as_ptr(&self) -> *mut u8 {
self.0.as_ptr()
}
/// Gets a [`PtrMut`] from this with a smaller lifetime.
#[inline]
pub fn reborrow(&mut self) -> PtrMut<'_, A> {
// SAFETY: the ptrmut we're borrowing from is assumed to be valid
unsafe { PtrMut::new(self.0) }
}
/// Gets an immutable reference from this mutable reference
#[inline]
pub fn as_ref(&self) -> Ptr<'_, A> {
// SAFETY: The `PtrMut` type's guarantees about the validity of this pointer are a superset of `Ptr` s guarantees
unsafe { Ptr::new(self.0) }
}
}
impl<'a, T> From<&'a mut T> for PtrMut<'a> {
#[inline]
fn from(val: &'a mut T) -> Self {
// SAFETY: The returned pointer has the same lifetime as the passed reference.
// The reference is mutable, and thus will not alias.
unsafe { Self::new(NonNull::from(val).cast()) }
}
}
impl<'a> OwningPtr<'a> {
/// Consumes a value and creates an [`OwningPtr`] to it while ensuring a double drop does not happen.
#[inline]
pub fn make<T, F: FnOnce(OwningPtr<'_>) -> R, R>(val: T, f: F) -> R {
let mut temp = ManuallyDrop::new(val);
// SAFETY: The value behind the pointer will not get dropped or observed later,
// so it's safe to promote it to an owning pointer.
f(unsafe { PtrMut::from(&mut *temp).promote() })
}
}
impl<'a, A: IsAligned> OwningPtr<'a, A> {
/// Creates a new instance from a raw pointer.
///
/// # Safety
/// - `inner` must point to valid value of whatever the pointee type is.
/// - If the `A` type parameter is [`Aligned`] then `inner` must be sufficiently aligned for the pointee type.
/// - `inner` must have correct provenance to allow read and writes of the pointee type.
/// - The lifetime `'a` must be constrained such that this [`OwningPtr`] will stay valid and nothing
/// else can read or mutate the pointee while this [`OwningPtr`] is live.
#[inline]
pub unsafe fn new(inner: NonNull<u8>) -> Self {
Self(inner, PhantomData)
}
/// Consumes the [`OwningPtr`] to obtain ownership of the underlying data of type `T`.
///
/// # Safety
/// - `T` must be the erased pointee type for this [`OwningPtr`].
/// - If the type parameter `A` is [`Unaligned`] then this pointer must be sufficiently aligned
/// for the pointee type `T`.
#[inline]
pub unsafe fn read<T>(self) -> T {
let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
// SAFETY: The caller ensure the pointee is of type `T` and uphold safety for `read`.
unsafe { ptr.read() }
}
/// Consumes the [`OwningPtr`] to drop the underlying data of type `T`.
///
/// # Safety
/// - `T` must be the erased pointee type for this [`OwningPtr`].
/// - If the type parameter `A` is [`Unaligned`] then this pointer must be sufficiently aligned
/// for the pointee type `T`.
#[inline]
pub unsafe fn drop_as<T>(self) {
let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
// SAFETY: The caller ensure the pointee is of type `T` and uphold safety for `drop_in_place`.
unsafe {
ptr.drop_in_place();
}
}
/// Gets the underlying pointer, erasing the associated lifetime.
///
/// If possible, it is strongly encouraged to use the other more type-safe functions
/// over this function.
#[inline]
#[allow(clippy::wrong_self_convention)]
pub fn as_ptr(&self) -> *mut u8 {
self.0.as_ptr()
}
/// Gets an immutable pointer from this owned pointer.
#[inline]
pub fn as_ref(&self) -> Ptr<'_, A> {
// SAFETY: The `Owning` type's guarantees about the validity of this pointer are a superset of `Ptr` s guarantees
unsafe { Ptr::new(self.0) }
}
/// Gets a mutable pointer from this owned pointer.
#[inline]
pub fn as_mut(&mut self) -> PtrMut<'_, A> {
// SAFETY: The `Owning` type's guarantees about the validity of this pointer are a superset of `Ptr` s guarantees
unsafe { PtrMut::new(self.0) }
}
}
impl<'a> OwningPtr<'a, Unaligned> {
/// Consumes the [`OwningPtr`] to obtain ownership of the underlying data of type `T`.
///
/// # Safety
/// - `T` must be the erased pointee type for this [`OwningPtr`].
pub unsafe fn read_unaligned<T>(self) -> T {
let ptr = self.as_ptr().cast::<T>();
// SAFETY: The caller ensure the pointee is of type `T` and uphold safety for `read_unaligned`.
unsafe { ptr.read_unaligned() }
}
}
/// Conceptually equivalent to `&'a [T]` but with length information cut out for performance reasons
pub struct ThinSlicePtr<'a, T> {
ptr: NonNull<T>,
#[cfg(debug_assertions)]
len: usize,
_marker: PhantomData<&'a [T]>,
}
impl<'a, T> ThinSlicePtr<'a, T> {
#[inline]
/// Indexes the slice without doing bounds checks
///
/// # Safety
/// `index` must be in-bounds.
pub unsafe fn get(self, index: usize) -> &'a T {
#[cfg(debug_assertions)]
debug_assert!(index < self.len);
let ptr = self.ptr.as_ptr();
// SAFETY: `index` is in-bounds so the resulting pointer is valid to dereference.
unsafe { &*ptr.add(index) }
}
}
impl<'a, T> Clone for ThinSlicePtr<'a, T> {
fn clone(&self) -> Self {
*self
}
}
impl<'a, T> Copy for ThinSlicePtr<'a, T> {}
impl<'a, T> From<&'a [T]> for ThinSlicePtr<'a, T> {
#[inline]
fn from(slice: &'a [T]) -> Self {
let ptr = slice.as_ptr().cast_mut();
Self {
// SAFETY: a reference can never be null
ptr: unsafe { NonNull::new_unchecked(ptr.debug_ensure_aligned()) },
#[cfg(debug_assertions)]
len: slice.len(),
_marker: PhantomData,
}
}
}
/// Creates a dangling pointer with specified alignment.
/// See [`NonNull::dangling`].
pub fn dangling_with_align(align: NonZeroUsize) -> NonNull<u8> {
debug_assert!(align.is_power_of_two(), "Alignment must be power of two.");
// SAFETY: The pointer will not be null, since it was created
// from the address of a `NonZeroUsize`.
unsafe { NonNull::new_unchecked(align.get() as *mut u8) }
}
mod private {
use core::cell::UnsafeCell;
pub trait SealedUnsafeCell {}
impl<'a, T> SealedUnsafeCell for &'a UnsafeCell<T> {}
}
/// Extension trait for helper methods on [`UnsafeCell`]
pub trait UnsafeCellDeref<'a, T>: private::SealedUnsafeCell {
/// # Safety
/// - The returned value must be unique and not alias any mutable or immutable references to the contents of the [`UnsafeCell`].
/// - At all times, you must avoid data races. If multiple threads have access to the same [`UnsafeCell`], then any writes must have a proper happens-before relation to all other accesses or use atomics ([`UnsafeCell`] docs for reference).
unsafe fn deref_mut(self) -> &'a mut T;
/// # Safety
/// - For the lifetime `'a` of the returned value you must not construct a mutable reference to the contents of the [`UnsafeCell`].
/// - At all times, you must avoid data races. If multiple threads have access to the same [`UnsafeCell`], then any writes must have a proper happens-before relation to all other accesses or use atomics ([`UnsafeCell`] docs for reference).
unsafe fn deref(self) -> &'a T;
/// Returns a copy of the contained value.
///
/// # Safety
/// - The [`UnsafeCell`] must not currently have a mutable reference to its content.
/// - At all times, you must avoid data races. If multiple threads have access to the same [`UnsafeCell`], then any writes must have a proper happens-before relation to all other accesses or use atomics ([`UnsafeCell`] docs for reference).
unsafe fn read(self) -> T
where
T: Copy;
}
impl<'a, T> UnsafeCellDeref<'a, T> for &'a UnsafeCell<T> {
#[inline]
unsafe fn deref_mut(self) -> &'a mut T {
// SAFETY: The caller upholds the alias rules.
unsafe { &mut *self.get() }
}
#[inline]
unsafe fn deref(self) -> &'a T {
// SAFETY: The caller upholds the alias rules.
unsafe { &*self.get() }
}
#[inline]
unsafe fn read(self) -> T
where
T: Copy,
{
// SAFETY: The caller upholds the alias rules.
unsafe { self.get().read() }
}
}
trait DebugEnsureAligned {
fn debug_ensure_aligned(self) -> Self;
}
// Disable this for miri runs as it already checks if pointer to reference
// casts are properly aligned.
#[cfg(all(debug_assertions, not(miri)))]
impl<T: Sized> DebugEnsureAligned for *mut T {
#[track_caller]
fn debug_ensure_aligned(self) -> Self {
let align = core::mem::align_of::<T>();
// Implementation shamelessly borrowed from the currently unstable
// ptr.is_aligned_to.
//
// Replace once https://github.com/rust-lang/rust/issues/96284 is stable.
assert_eq!(
self as usize & (align - 1),
0,
"pointer is not aligned. Address {:p} does not have alignment {} for type {}",
self,
align,
core::any::type_name::<T>()
);
self
}
}
#[cfg(any(not(debug_assertions), miri))]
impl<T: Sized> DebugEnsureAligned for *mut T {
#[inline(always)]
fn debug_ensure_aligned(self) -> Self {
self
}
}