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document remaining unsafety in maybe_uninit.rs

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This commit is contained in:
Ralf Jung 2020-09-02 10:00:08 +02:00
parent cff5f56886
commit 35068326b5
1 changed files with 4 additions and 6 deletions
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10
library/core/src/mem/maybe_uninit.rs
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@ -3,8 +3,6 @@ use crate::fmt;
use crate::intrinsics;
use crate::mem::ManuallyDrop;
// ignore-tidy-undocumented-unsafe
/// A wrapper type to construct uninitialized instances of `T`.
///
/// # Initialization invariant
@ -355,6 +353,7 @@ impl<T> MaybeUninit<T> {
#[rustc_diagnostic_item = "maybe_uninit_zeroed"]
pub fn zeroed() -> MaybeUninit<T> {
let mut u = MaybeUninit::<T>::uninit();
// SAFETY: `u.as_mut_ptr()` points to allocated memory.
unsafe {
u.as_mut_ptr().write_bytes(0u8, 1);
}
@ -368,10 +367,9 @@ impl<T> MaybeUninit<T> {
#[unstable(feature = "maybe_uninit_extra", issue = "63567")]
#[inline(always)]
pub fn write(&mut self, val: T) -> &mut T {
unsafe {
self.value = ManuallyDrop::new(val);
self.assume_init_mut()
}
*self = MaybeUninit::new(val);
// SAFETY: We just initialized this value.
unsafe { self.assume_init_mut() }
}
/// Gets a pointer to the contained value. Reading from this pointer or turning it