Port rust-lang/rust#50487: Use ManuallyDrop instead of Option

Author: clint-white

src/binary_heap.rs

@@ -170,7 +170,7 @@ use std::slice;
 // use std::vec::Drain;
 use compare::Compare;
 use core::fmt;
-use core::mem::{size_of, swap};
+use core::mem::{size_of, swap, ManuallyDrop};
 use core::ptr;
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
@@ -1286,8 +1286,7 @@ impl<T, C: Compare<T>> BinaryHeap<T, C> {
 /// position with the value that was originally removed.
 struct Hole<'a, T: 'a> {
     data: &'a mut [T],
-    /// `elt` is always `Some` from new until drop.
-    elt: Option<T>,
+    elt: ManuallyDrop<T>,
     pos: usize,
 }
 
@@ -1302,7 +1301,7 @@ impl<'a, T> Hole<'a, T> {
         let elt = unsafe { ptr::read(data.get_unchecked(pos)) };
         Hole {
             data,
-            elt: Some(elt),
+            elt: ManuallyDrop::new(elt),
             pos,
         }
     }
@@ -1315,7 +1314,7 @@ impl<'a, T> Hole<'a, T> {
     /// Returns a reference to the element removed.
     #[inline]
     fn element(&self) -> &T {
-        self.elt.as_ref().unwrap()
+        &self.elt
     }
 
     /// Returns a reference to the element at `index`.
@@ -1351,7 +1350,7 @@ impl<'a, T> Drop for Hole<'a, T> {
         // fill the hole again
         unsafe {
             let pos = self.pos;
-            ptr::write(self.data.get_unchecked_mut(pos), self.elt.take().unwrap());
+            ptr::copy_nonoverlapping(&*self.elt, self.data.get_unchecked_mut(pos), 1);
         }
     }
 }