Merge #34

34: add BinaryHeap.pop_unchecked r=japaric a=japaric



Co-authored-by: Jorge Aparicio <jorge@japaric.io>

src/binary_heap.rs

@@ -10,6 +10,7 @@
 
 use core::cmp::Ordering;
 use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
 use core::{mem, ptr, slice};
 
 use generic_array::ArrayLength;
@@ -249,13 +250,23 @@ where
     /// assert_eq!(heap.pop(), None);
     /// ```
     pub fn pop(&mut self) -> Option<T> {
-        self.data.pop().map(|mut item| {
-            if !self.is_empty() {
-                mem::swap(&mut item, &mut self.data[0]);
-                self.sift_down_to_bottom(0);
-            }
-            item
-        })
+        if self.is_empty() {
+            None
+        } else {
+            Some(unsafe { self.pop_unchecked() })
+        }
+    }
+
+    /// Removes the *top* (greatest if max-heap, smallest if min-heap) item from the binary heap and
+    /// returns it, without checking if the binary heap is empty.
+    pub unsafe fn pop_unchecked(&mut self) -> T {
+        let mut item = self.data.pop_unchecked();
+
+        if !self.is_empty() {
+            mem::swap(&mut item, &mut self.data[0]);
+            self.sift_down_to_bottom(0);
+        }
+        item
     }
 
     /// Pushes an item onto the binary heap.
@@ -333,7 +344,7 @@ where
 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,
 }
 
@@ -347,7 +358,7 @@ impl<'a, T> Hole<'a, T> {
         let elt = ptr::read(data.get_unchecked(pos));
         Hole {
             data,
-            elt: Some(elt),
+            elt: ManuallyDrop::new(elt),
             pos,
         }
     }
@@ -360,7 +371,7 @@ 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`.
@@ -393,7 +404,7 @@ 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::write(self.data.get_unchecked_mut(pos), ptr::read(&*self.elt));
         }
     }
 }