Re-introduce covariance for containers

Author: sosthene-nitrokey

src/binary_heap.rs

@@ -17,10 +17,7 @@ use core::{
     ptr, slice,
 };
 
-use crate::{
-    storage::{OwnedStorage, Storage, ViewStorage},
-    vec::{Vec, VecInner},
-};
+use crate::vec::{OwnedVecStorage, Vec, VecInner, VecStorage, ViewVecStorage};
 
 /// Min-heap
 pub enum Min {}
@@ -54,11 +51,11 @@ mod private {
 impl private::Sealed for Max {}
 impl private::Sealed for Min {}
 
-/// Base struct for [`BinaryHeap`] and [`BinaryHeapView`], generic over the [`Storage`].
+/// Base struct for [`BinaryHeap`] and [`BinaryHeapView`], generic over the [`VecStorage`].
 ///
 /// In most cases you should use [`BinaryHeap`] or [`BinaryHeapView`] directly. Only use this
 /// struct if you want to write code that's generic over both.
-pub struct BinaryHeapInner<T, K, S: Storage> {
+pub struct BinaryHeapInner<T, K, S: VecStorage<T> + ?Sized> {
     pub(crate) _kind: PhantomData<K>,
     pub(crate) data: VecInner<T, S>,
 }
@@ -109,7 +106,7 @@ pub struct BinaryHeapInner<T, K, S: Storage> {
 /// // The heap should now be empty.
 /// assert!(heap.is_empty())
 /// ```
-pub type BinaryHeap<T, K, const N: usize> = BinaryHeapInner<T, K, OwnedStorage<N>>;
+pub type BinaryHeap<T, K, const N: usize> = BinaryHeapInner<T, K, OwnedVecStorage<T, N>>;
 
 /// A priority queue implemented with a binary heap.
 ///
@@ -158,7 +155,7 @@ pub type BinaryHeap<T, K, const N: usize> = BinaryHeapInner<T, K, OwnedStorage<N
 /// // The heap should now be empty.
 /// assert!(heap.is_empty())
 /// ```
-pub type BinaryHeapView<T, K> = BinaryHeapInner<T, K, ViewStorage>;
+pub type BinaryHeapView<T, K> = BinaryHeapInner<T, K, ViewVecStorage<T>>;
 
 impl<T, K, const N: usize> BinaryHeap<T, K, N> {
     /* Constructors */
@@ -198,7 +195,7 @@ impl<T, K, const N: usize> BinaryHeap<T, K, N> {
     }
 }
 
-impl<T, K, S: Storage> BinaryHeapInner<T, K, S>
+impl<T, K, S: VecStorage<T> + ?Sized> BinaryHeapInner<T, K, S>
 where
     T: Ord,
     K: Kind,
@@ -519,7 +516,7 @@ pub struct PeekMutInner<'a, T, K, S>
 where
     T: Ord,
     K: Kind,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     heap: &'a mut BinaryHeapInner<T, K, S>,
     sift: bool,
@@ -530,20 +527,20 @@ where
 ///
 /// This `struct` is created by [`BinaryHeap::peek_mut`].
 /// See its documentation for more.
-pub type PeekMut<'a, T, K, const N: usize> = PeekMutInner<'a, T, K, OwnedStorage<N>>;
+pub type PeekMut<'a, T, K, const N: usize> = PeekMutInner<'a, T, K, OwnedVecStorage<T, N>>;
 
 /// Structure wrapping a mutable reference to the greatest item on a
 /// `BinaryHeap`.
 ///
 /// This `struct` is created by [`BinaryHeapView::peek_mut`].
 /// See its documentation for more.
-pub type PeekMutView<'a, T, K> = PeekMutInner<'a, T, K, ViewStorage>;
+pub type PeekMutView<'a, T, K> = PeekMutInner<'a, T, K, ViewVecStorage<T>>;
 
 impl<T, K, S> Drop for PeekMutInner<'_, T, K, S>
 where
     T: Ord,
     K: Kind,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     fn drop(&mut self) {
         if self.sift {
@@ -556,7 +553,7 @@ impl<T, K, S> Deref for PeekMutInner<'_, T, K, S>
 where
     T: Ord,
     K: Kind,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     type Target = T;
     fn deref(&self) -> &T {
@@ -570,7 +567,7 @@ impl<T, K, S> DerefMut for PeekMutInner<'_, T, K, S>
 where
     T: Ord,
     K: Kind,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     fn deref_mut(&mut self) -> &mut T {
         debug_assert!(!self.heap.is_empty());
@@ -583,7 +580,7 @@ impl<'a, T, K, S> PeekMutInner<'a, T, K, S>
 where
     T: Ord,
     K: Kind,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     /// Removes the peeked value from the heap and returns it.
     pub fn pop(mut this: PeekMutInner<'a, T, K, S>) -> T {
@@ -631,7 +628,7 @@ impl<T, K, S> fmt::Debug for BinaryHeapInner<T, K, S>
 where
     K: Kind,
     T: Ord + fmt::Debug,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_list().entries(self.iter()).finish()
@@ -642,7 +639,7 @@ impl<'a, T, K, S> IntoIterator for &'a BinaryHeapInner<T, K, S>
 where
     K: Kind,
     T: Ord,
-    S: Storage,
+    S: VecStorage<T> + ?Sized,
 {
     type Item = &'a T;
     type IntoIter = slice::Iter<'a, T>;
@@ -656,7 +653,7 @@ where
 mod tests {
     use static_assertions::assert_not_impl_any;
 
-    use super::{BinaryHeap, Max, Min};
+    use super::{BinaryHeap, BinaryHeapView, Max, Min};
 
     // Ensure a `BinaryHeap` containing `!Send` values stays `!Send` itself.
     assert_not_impl_any!(BinaryHeap<*const (), Max, 4>: Send);
@@ -829,4 +826,13 @@ mod tests {
         assert_eq!(heap.pop(), Some(1));
         assert_eq!(heap.pop(), None);
     }
+
+    fn _test_variance<'a: 'b, 'b>(x: BinaryHeap<&'a (), Max, 42>) -> BinaryHeap<&'b (), Max, 42> {
+        x
+    }
+    fn _test_variance_view<'a: 'b, 'b, 'c>(
+        x: &'c BinaryHeapView<&'a (), Max>,
+    ) -> &'c BinaryHeapView<&'b (), Max> {
+        x
+    }
 }

src/deque.rs

@@ -33,19 +33,21 @@
 //! }
 //! ```
 
-use core::borrow::{Borrow, BorrowMut};
 use core::fmt;
 use core::iter::FusedIterator;
+use core::marker::PhantomData;
 use core::mem::MaybeUninit;
 use core::{ptr, slice};
 
-use crate::storage::{OwnedStorage, Storage, ViewStorage};
+use crate::vec::{OwnedVecStorage, VecStorage, VecStorageInner, ViewVecStorage};
 
-/// Base struct for [`Deque`] and [`Deque`], generic over the [`Storage`].
+/// Base struct for [`Deque`] and [`Deque`], generic over the [`VecStorage`].
 ///
 /// In most cases you should use [`Deque`] or [`Deque`] directly. Only use this
 /// struct if you want to write code that's generic over both.
-pub struct DequeInner<T, S: Storage> {
+pub struct DequeInner<T, S: VecStorage<T> + ?Sized> {
+    // This phantomdata is required because otherwise rustc thinks that `T` is not used
+    phantom: PhantomData<T>,
     /// Front index. Always 0..=(N-1)
     front: usize,
     /// Back index. Always 0..=(N-1).
@@ -54,7 +56,7 @@ pub struct DequeInner<T, S: Storage> {
     /// Used to distinguish "empty" and "full" cases when `front == back`.
     /// May only be `true` if `front == back`, always `false` otherwise.
     full: bool,
-    buffer: S::Buffer<MaybeUninit<T>>,
+    buffer: S,
 }
 
 /// A fixed capacity double-ended queue.
@@ -91,7 +93,7 @@ pub struct DequeInner<T, S: Storage> {
 ///     println!("{}", x);
 /// }
 /// ```
-pub type Deque<T, const N: usize> = DequeInner<T, OwnedStorage<N>>;
+pub type Deque<T, const N: usize> = DequeInner<T, OwnedVecStorage<T, N>>;
 
 /// A double-ended queue with dynamic capacity.
 ///
@@ -130,7 +132,7 @@ pub type Deque<T, const N: usize> = DequeInner<T, OwnedStorage<N>>;
 ///     println!("{}", x);
 /// }
 /// ```
-pub type DequeView<T> = DequeInner<T, ViewStorage>;
+pub type DequeView<T> = DequeInner<T, ViewVecStorage<T>>;
 
 impl<T, const N: usize> Deque<T, N> {
     const INIT: MaybeUninit<T> = MaybeUninit::uninit();
@@ -153,7 +155,10 @@ impl<T, const N: usize> Deque<T, N> {
         crate::sealed::greater_than_0::<N>();
 
         Self {
-            buffer: [Self::INIT; N],
+            phantom: PhantomData,
+            buffer: VecStorageInner {
+                buffer: [Self::INIT; N],
+            },
             front: 0,
             back: 0,
             full: false,
@@ -191,7 +196,7 @@ impl<T, const N: usize> Deque<T, N> {
     }
 }
 
-impl<T, S: Storage> DequeInner<T, S> {
+impl<T, S: VecStorage<T> + ?Sized> DequeInner<T, S> {
     /// Returns the maximum number of elements the deque can hold.
     pub fn storage_capacity(&self) -> usize {
         self.buffer.borrow().len()
@@ -794,29 +799,29 @@ impl<T, const N: usize> Default for Deque<T, N> {
     }
 }
 
-impl<T, S: Storage> Drop for DequeInner<T, S> {
+impl<T, S: VecStorage<T> + ?Sized> Drop for DequeInner<T, S> {
     fn drop(&mut self) {
         // safety: `self` is left in an inconsistent state but it doesn't matter since
         // it's getting dropped. Nothing should be able to observe `self` after drop.
         unsafe { self.drop_contents() }
     }
 }
 
-impl<T: fmt::Debug, S: Storage> fmt::Debug for DequeInner<T, S> {
+impl<T: fmt::Debug, S: VecStorage<T> + ?Sized> fmt::Debug for DequeInner<T, S> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_list().entries(self).finish()
     }
 }
 
 /// As with the standard library's `VecDeque`, items are added via `push_back`.
-impl<T, S: Storage> Extend<T> for DequeInner<T, S> {
+impl<T, S: VecStorage<T> + ?Sized> Extend<T> for DequeInner<T, S> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         for item in iter {
             self.push_back(item).ok().unwrap();
         }
     }
 }
-impl<'a, T: 'a + Copy, S: Storage> Extend<&'a T> for DequeInner<T, S> {
+impl<'a, T: 'a + Copy, S: VecStorage<T> + ?Sized> Extend<&'a T> for DequeInner<T, S> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().copied())
     }
@@ -846,7 +851,7 @@ impl<T, const N: usize> IntoIterator for Deque<T, N> {
     }
 }
 
-impl<'a, T, S: Storage> IntoIterator for &'a DequeInner<T, S> {
+impl<'a, T, S: VecStorage<T> + ?Sized> IntoIterator for &'a DequeInner<T, S> {
     type Item = &'a T;
     type IntoIter = Iter<'a, T>;
 
@@ -855,7 +860,7 @@ impl<'a, T, S: Storage> IntoIterator for &'a DequeInner<T, S> {
     }
 }
 
-impl<'a, T, S: Storage> IntoIterator for &'a mut DequeInner<T, S> {
+impl<'a, T, S: VecStorage<T> + ?Sized> IntoIterator for &'a mut DequeInner<T, S> {
     type Item = &'a mut T;
     type IntoIter = IterMut<'a, T>;