1 files changed, 162 insertions, 0 deletions
diff --git a/library/alloc/src/collections/vec_deque/iter_mut.rs b/library/alloc/src/collections/vec_deque/iter_mut.rs
new file mode 100644
index 000000000..b78c0d5e1
--- /dev/null
+++ b/library/alloc/src/collections/vec_deque/iter_mut.rs
@@ -0,0 +1,162 @@
+use core::fmt;
+use core::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
+use core::marker::PhantomData;
+
+use super::{count, wrap_index, RingSlices};
+
+/// A mutable iterator over the elements of a `VecDeque`.
+///
+/// This `struct` is created by the [`iter_mut`] method on [`super::VecDeque`]. See its
+/// documentation for more.
+///
+/// [`iter_mut`]: super::VecDeque::iter_mut
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IterMut<'a, T: 'a> {
+    // Internal safety invariant: the entire slice is dereferenceable.
+    ring: *mut [T],
+    tail: usize,
+    head: usize,
+    phantom: PhantomData<&'a mut [T]>,
+}
+
+impl<'a, T> IterMut<'a, T> {
+    pub(super) unsafe fn new(
+        ring: *mut [T],
+        tail: usize,
+        head: usize,
+        phantom: PhantomData<&'a mut [T]>,
+    ) -> Self {
+        IterMut { ring, tail, head, phantom }
+    }
+}
+
+// SAFETY: we do nothing thread-local and there is no interior mutability,
+// so the usual structural `Send`/`Sync` apply.
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for IterMut<'_, T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Sync for IterMut<'_, T> {}
+
+#[stable(feature = "collection_debug", since = "1.17.0")]
+impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
+        // SAFETY: these are the elements we have not handed out yet, so aliasing is fine.
+        // The `IterMut` invariant also ensures everything is dereferenceable.
+        let (front, back) = unsafe { (&*front, &*back) };
+        f.debug_tuple("IterMut").field(&front).field(&back).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for IterMut<'a, T> {
+    type Item = &'a mut T;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut T> {
+        if self.tail == self.head {
+            return None;
+        }
+        let tail = self.tail;
+        self.tail = wrap_index(self.tail.wrapping_add(1), self.ring.len());
+
+        unsafe {
+            let elem = self.ring.get_unchecked_mut(tail);
+            Some(&mut *elem)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = count(self.tail, self.head, self.ring.len());
+        (len, Some(len))
+    }
+
+    fn fold<Acc, F>(self, mut accum: Acc, mut f: F) -> Acc
+    where
+        F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
+        // SAFETY: these are the elements we have not handed out yet, so aliasing is fine.
+        // The `IterMut` invariant also ensures everything is dereferenceable.
+        let (front, back) = unsafe { (&mut *front, &mut *back) };
+        accum = front.iter_mut().fold(accum, &mut f);
+        back.iter_mut().fold(accum, &mut f)
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        if n >= count(self.tail, self.head, self.ring.len()) {
+            self.tail = self.head;
+            None
+        } else {
+            self.tail = wrap_index(self.tail.wrapping_add(n), self.ring.len());
+            self.next()
+        }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<&'a mut T> {
+        self.next_back()
+    }
+
+    #[inline]
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        // Safety: The TrustedRandomAccess contract requires that callers only pass an index
+        // that is in bounds.
+        unsafe {
+            let idx = wrap_index(self.tail.wrapping_add(idx), self.ring.len());
+            &mut *self.ring.get_unchecked_mut(idx)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut T> {
+        if self.tail == self.head {
+            return None;
+        }
+        self.head = wrap_index(self.head.wrapping_sub(1), self.ring.len());
+
+        unsafe {
+            let elem = self.ring.get_unchecked_mut(self.head);
+            Some(&mut *elem)
+        }
+    }
+
+    fn rfold<Acc, F>(self, mut accum: Acc, mut f: F) -> Acc
+    where
+        F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
+        // SAFETY: these are the elements we have not handed out yet, so aliasing is fine.
+        // The `IterMut` invariant also ensures everything is dereferenceable.
+        let (front, back) = unsafe { (&mut *front, &mut *back) };
+        accum = back.iter_mut().rfold(accum, &mut f);
+        front.iter_mut().rfold(accum, &mut f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for IterMut<'_, T> {
+    fn is_empty(&self) -> bool {
+        self.head == self.tail
+    }
+}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<T> FusedIterator for IterMut<'_, T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for IterMut<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<T> TrustedRandomAccess for IterMut<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<T> TrustedRandomAccessNoCoerce for IterMut<'_, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}