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Put Pin::as_deref_mut in impl Pin<Ptr>

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Noa 2024-08-22 14:42:24 -05:00
parent 5ad98b4026
commit b968b26c03
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1 changed files with 62 additions and 59 deletions
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121
library/core/src/pin.rs
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@ -1291,8 +1291,8 @@ impl<Ptr: Deref> Pin<Ptr> {
/// // Now, if `x` was the only reference, we have a mutable reference to /// // Now, if `x` was the only reference, we have a mutable reference to
/// // data that we pinned above, which we could use to move it as we have /// // data that we pinned above, which we could use to move it as we have
/// // seen in the previous example. We have violated the pinning API contract. /// // seen in the previous example. We have violated the pinning API contract.
/// } /// }
/// ``` /// ```
/// ///
/// ## Pinning of closure captures /// ## Pinning of closure captures
/// ///
@ -1356,20 +1356,6 @@ impl<Ptr: Deref> Pin<Ptr> {
Pin { __pointer: pointer } Pin { __pointer: pointer }
} }
/// Gets a shared reference to the pinned value this [`Pin`] points to.
///
/// This is a generic method to go from `&Pin<Pointer<T>>` to `Pin<&T>`.
/// It is safe because, as part of the contract of `Pin::new_unchecked`,
/// the pointee cannot move after `Pin<Pointer<T>>` got created.
/// "Malicious" implementations of `Pointer::Deref` are likewise
/// ruled out by the contract of `Pin::new_unchecked`.
#[stable(feature = "pin", since = "1.33.0")]
#[inline(always)]
pub fn as_ref(&self) -> Pin<&Ptr::Target> {
// SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&*self.__pointer) }
}
/// Unwraps this `Pin<Ptr>`, returning the underlying `Ptr`. /// Unwraps this `Pin<Ptr>`, returning the underlying `Ptr`.
/// ///
/// # Safety /// # Safety
@ -1394,9 +1380,21 @@ pub fn as_ref(&self) -> Pin<&Ptr::Target> {
pub const unsafe fn into_inner_unchecked(pin: Pin<Ptr>) -> Ptr { pub const unsafe fn into_inner_unchecked(pin: Pin<Ptr>) -> Ptr {
pin.__pointer pin.__pointer
} }
}
impl<Ptr: DerefMut> Pin<Ptr> { /// Gets a shared reference to the pinned value this [`Pin`] points to.
///
/// This is a generic method to go from `&Pin<Pointer<T>>` to `Pin<&T>`.
/// It is safe because, as part of the contract of `Pin::new_unchecked`,
/// the pointee cannot move after `Pin<Pointer<T>>` got created.
/// "Malicious" implementations of `Pointer::Deref` are likewise
/// ruled out by the contract of `Pin::new_unchecked`.
#[stable(feature = "pin", since = "1.33.0")]
#[inline(always)]
pub fn as_ref(&self) -> Pin<&Ptr::Target> {
// SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&*self.__pointer) }
}
/// Gets a mutable reference to the pinned value this `Pin<Ptr>` points to. /// Gets a mutable reference to the pinned value this `Pin<Ptr>` points to.
/// ///
/// This is a generic method to go from `&mut Pin<Pointer<T>>` to `Pin<&mut T>`. /// This is a generic method to go from `&mut Pin<Pointer<T>>` to `Pin<&mut T>`.
@ -1428,11 +1426,55 @@ impl<Ptr: DerefMut> Pin<Ptr> {
/// ``` /// ```
#[stable(feature = "pin", since = "1.33.0")] #[stable(feature = "pin", since = "1.33.0")]
#[inline(always)] #[inline(always)]
pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target> { pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target>
where
Ptr: DerefMut,
{
// SAFETY: see documentation on this function // SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&mut *self.__pointer) } unsafe { Pin::new_unchecked(&mut *self.__pointer) }
} }
/// Gets `Pin<&mut T>` to the underlying pinned value from this nested `Pin`-pointer.
///
/// This is a generic method to go from `Pin<&mut Pin<Pointer<T>>>` to `Pin<&mut T>`. It is
/// safe because the existence of a `Pin<Pointer<T>>` ensures that the pointee, `T`, cannot
/// move in the future, and this method does not enable the pointee to move. "Malicious"
/// implementations of `Ptr::DerefMut` are likewise ruled out by the contract of
/// `Pin::new_unchecked`.
#[unstable(feature = "pin_deref_mut", issue = "86918")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline(always)]
pub fn as_deref_mut(self: Pin<&mut Pin<Ptr>>) -> Pin<&mut Ptr::Target>
where
Ptr: DerefMut,
{
// SAFETY: What we're asserting here is that going from
//
// Pin<&mut Pin<Ptr>>
//
// to
//
// Pin<&mut Ptr::Target>
//
// is safe.
//
// We need to ensure that two things hold for that to be the case:
//
// 1) Once we give out a `Pin<&mut Ptr::Target>`, a `&mut Ptr::Target` will not be given out.
// 2) By giving out a `Pin<&mut Ptr::Target>`, we do not risk violating
// `Pin<&mut Pin<Ptr>>`
//
// The existence of `Pin<Ptr>` is sufficient to guarantee #1: since we already have a
// `Pin<Ptr>`, it must already uphold the pinning guarantees, which must mean that
// `Pin<&mut Ptr::Target>` does as well, since `Pin::as_mut` is safe. We do not have to rely
// on the fact that `Ptr` is _also_ pinned.
//
// For #2, we need to ensure that code given a `Pin<&mut Ptr::Target>` cannot cause the
// `Pin<Ptr>` to move? That is not possible, since `Pin<&mut Ptr::Target>` no longer retains
// any access to the `Ptr` itself, much less the `Pin<Ptr>`.
unsafe { self.get_unchecked_mut() }.as_mut()
}
/// Assigns a new value to the memory location pointed to by the `Pin<Ptr>`. /// Assigns a new value to the memory location pointed to by the `Pin<Ptr>`.
/// ///
/// This overwrites pinned data, but that is okay: the original pinned value's destructor gets /// This overwrites pinned data, but that is okay: the original pinned value's destructor gets
@ -1457,6 +1499,7 @@ pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target> {
#[inline(always)] #[inline(always)]
pub fn set(&mut self, value: Ptr::Target) pub fn set(&mut self, value: Ptr::Target)
where where
Ptr: DerefMut,
Ptr::Target: Sized, Ptr::Target: Sized,
{ {
*(self.__pointer) = value; *(self.__pointer) = value;
@ -1613,46 +1656,6 @@ pub const fn static_ref(r: &'static T) -> Pin<&'static T> {
} }
} }
impl<'a, Ptr: DerefMut> Pin<&'a mut Pin<Ptr>> {
/// Gets `Pin<&mut T>` to the underlying pinned value from this nested `Pin`-pointer.
///
/// This is a generic method to go from `Pin<&mut Pin<Pointer<T>>>` to `Pin<&mut T>`. It is
/// safe because the existence of a `Pin<Pointer<T>>` ensures that the pointee, `T`, cannot
/// move in the future, and this method does not enable the pointee to move. "Malicious"
/// implementations of `Ptr::DerefMut` are likewise ruled out by the contract of
/// `Pin::new_unchecked`.
#[unstable(feature = "pin_deref_mut", issue = "86918")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline(always)]
pub fn as_deref_mut(self) -> Pin<&'a mut Ptr::Target> {
// SAFETY: What we're asserting here is that going from
//
// Pin<&mut Pin<Ptr>>
//
// to
//
// Pin<&mut Ptr::Target>
//
// is safe.
//
// We need to ensure that two things hold for that to be the case:
//
// 1) Once we give out a `Pin<&mut Ptr::Target>`, a `&mut Ptr::Target` will not be given out.
// 2) By giving out a `Pin<&mut Ptr::Target>`, we do not risk violating
// `Pin<&mut Pin<Ptr>>`
//
// The existence of `Pin<Ptr>` is sufficient to guarantee #1: since we already have a
// `Pin<Ptr>`, it must already uphold the pinning guarantees, which must mean that
// `Pin<&mut Ptr::Target>` does as well, since `Pin::as_mut` is safe. We do not have to rely
// on the fact that `Ptr` is _also_ pinned.
//
// For #2, we need to ensure that code given a `Pin<&mut Ptr::Target>` cannot cause the
// `Pin<Ptr>` to move? That is not possible, since `Pin<&mut Ptr::Target>` no longer retains
// any access to the `Ptr` itself, much less the `Pin<Ptr>`.
unsafe { self.get_unchecked_mut() }.as_mut()
}
}
impl<T: ?Sized> Pin<&'static mut T> { impl<T: ?Sized> Pin<&'static mut T> {
/// Gets a pinning mutable reference from a static mutable reference. /// Gets a pinning mutable reference from a static mutable reference.
/// ///