X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;f=src%2Flibcore%2Fcell.rs;h=e3292ecc1d1871c0cd8bb4efb1e50a013250b5ed;hb=aba385abbd69146387893c84951a06ec283f4d10;hp=fda103a52d8bc851b8fa4d07f277eb27302d425f;hpb=f01ffbc7f14c5e80c130d679e99c3507591e4bab;p=rust.git

diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index fda103a52d8..e3292ecc1d1 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -137,9 +137,11 @@
 //! use std::cell::Cell;
 //! use std::ptr::NonNull;
 //! use std::intrinsics::abort;
+//! use std::marker::PhantomData;
 //!
 //! struct Rc<T: ?Sized> {
-//!     ptr: NonNull<RcBox<T>>
+//!     ptr: NonNull<RcBox<T>>,
+//!     phantom: PhantomData<RcBox<T>>,
 //! }
 //!
 //! struct RcBox<T: ?Sized> {
@@ -151,7 +153,10 @@
 //! impl<T: ?Sized> Clone for Rc<T> {
 //!     fn clone(&self) -> Rc<T> {
 //!         self.inc_strong();
-//!         Rc { ptr: self.ptr }
+//!         Rc {
+//!             ptr: self.ptr,
+//!             phantom: PhantomData,
+//!         }
 //!     }
 //! }
 //!
@@ -182,6 +187,8 @@
 //! ```
 //!
 
+// ignore-tidy-undocumented-unsafe
+
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::cmp::Ordering;
@@ -1541,6 +1548,36 @@ pub const fn get(&self) -> *mut T {
         // #[repr(transparent)]
         self as *const UnsafeCell<T> as *const T as *mut T
     }
+
+    /// Gets a mutable pointer to the wrapped value.
+    ///
+    /// This can be cast to a pointer of any kind.
+    /// Ensure that the access is unique (no active references, mutable or not)
+    /// when casting to `&mut T`, and ensure that there are no mutations
+    /// or mutable aliases going on when casting to `&T`.
+    ///
+    /// # Examples
+    ///
+    /// Gradual initialization of an `UnsafeCell`:
+    ///
+    /// ```
+    /// #![feature(unsafe_cell_raw_get)]
+    /// use std::cell::UnsafeCell;
+    /// use std::mem::MaybeUninit;
+    ///
+    /// let m = MaybeUninit::<UnsafeCell<i32>>::uninit();
+    /// unsafe { m.as_ptr().raw_get().write(5); }
+    /// let uc = unsafe { m.assume_init() };
+    ///
+    /// assert_eq!(uc.into_inner(), 5);
+    /// ```
+    #[inline]
+    #[unstable(feature = "unsafe_cell_raw_get", issue = "0")]
+    pub const fn raw_get(self: *const Self) -> *mut T {
+        // We can just cast the pointer from `UnsafeCell<T>` to `T` because of
+        // #[repr(transparent)]
+        self as *const T as *mut T
+    }
 }
 
 #[stable(feature = "unsafe_cell_default", since = "1.10.0")]