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clarify why we can do the ptr cast

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Ralf Jung
2019-11-13 09:07:52 +01:00
parent aba385abbd
commit 19ebe2fb6d
1 changed files with 5 additions and 3 deletions
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8
src/libcore/cell.rs
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@@ -1545,7 +1545,8 @@ impl<T: ?Sized> UnsafeCell<T> {
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub const fn get(&self) -> *mut T { pub const fn get(&self) -> *mut T {
// We can just cast the pointer from `UnsafeCell<T>` to `T` because of // We can just cast the pointer from `UnsafeCell<T>` to `T` because of
// #[repr(transparent)] // #[repr(transparent)]. This exploits libstd's special status, there is
// no guarantee for user code that this will work in future versions of the compiler!
self as *const UnsafeCell<T> as *const T as *mut T self as *const UnsafeCell<T> as *const T as *mut T
} }
@@ -1572,10 +1573,11 @@ impl<T: ?Sized> UnsafeCell<T> {
/// assert_eq!(uc.into_inner(), 5); /// assert_eq!(uc.into_inner(), 5);
/// ``` /// ```
#[inline] #[inline]
#[unstable(feature = "unsafe_cell_raw_get", issue = "0")] #[unstable(feature = "unsafe_cell_raw_get", issue = "66358")]
pub const fn raw_get(self: *const Self) -> *mut T { pub const fn raw_get(self: *const Self) -> *mut T {
// We can just cast the pointer from `UnsafeCell<T>` to `T` because of // We can just cast the pointer from `UnsafeCell<T>` to `T` because of
// #[repr(transparent)] // #[repr(transparent)]. This exploits libstd's special status, there is
// no guarantee for user code that this will work in future versions of the compiler!
self as *const T as *mut T self as *const T as *mut T
} }
} }