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remove bogus example from drop_in_place #62351

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Jul 4, 2019
Merged

remove bogus example from drop_in_place #62351

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32 changes: 5 additions & 27 deletions src/libcore/ptr/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,16 +100,19 @@ pub use unique::Unique;
/// as the compiler doesn't need to prove that it's sound to elide the
/// copy.
///
/// Unaligned values cannot be dropped in place, they must be copied to an aligned
/// location first using [`ptr::read_unaligned`].
///
/// [`ptr::read`]: ../ptr/fn.read.html
/// [`ptr::read_unaligned`]: ../ptr/fn.read_unaligned.html
///
/// # Safety
///
/// Behavior is undefined if any of the following conditions are violated:
///
/// * `to_drop` must be [valid] for reads.
///
/// * `to_drop` must be properly aligned. See the example below for how to drop
/// an unaligned pointer.
/// * `to_drop` must be properly aligned.
///
/// Additionally, if `T` is not [`Copy`], using the pointed-to value after
/// calling `drop_in_place` can cause undefined behavior. Note that `*to_drop =
Expand Down Expand Up @@ -153,31 +156,6 @@ pub use unique::Unique;
/// assert!(weak.upgrade().is_none());
/// ```
///
/// Unaligned values cannot be dropped in place, they must be copied to an aligned
/// location first:
/// ```
/// use std::ptr;
/// use std::mem::{self, MaybeUninit};
///
/// unsafe fn drop_after_copy<T>(to_drop: *mut T) {
/// let mut copy: MaybeUninit<T> = MaybeUninit::uninit();
/// ptr::copy(to_drop, copy.as_mut_ptr(), 1);
/// drop(copy.assume_init());
/// }
///
/// #[repr(packed, C)]
/// struct Packed {
/// _padding: u8,
/// unaligned: Vec<i32>,
/// }
///
/// let mut p = Packed { _padding: 0, unaligned: vec![42] };
/// unsafe {
/// drop_after_copy(&mut p.unaligned as *mut _);
/// mem::forget(p);
/// }
/// ```
///
/// Notice that the compiler performs this copy automatically when dropping packed structs,
/// i.e., you do not usually have to worry about such issues unless you call `drop_in_place`
/// manually.
Expand Down