Use array::IntoIter for the ArrayChunks remainder

Author: rossmacarthur

library/core/src/array/iter.rs

@@ -84,6 +84,16 @@ impl<T, const N: usize> IntoIter<T, N> {
  IntoIterator::into_iter(array)
  }
 
+ /// Creates a new iterator from a partially initalized array.
+ ///
+ /// # Safety
+ ///
+ /// The caller must guarantee that all and only the `alive` elements of
+ /// `data` are initialized.
+ pub(crate) unsafe fn with_partial(data: [MaybeUninit<T>; N], alive: Range<usize>) -> Self {
+ Self { data, alive }
+ }
+
  /// Creates an iterator over the elements in a partially-initialized buffer.
  ///
  /// If you have a fully-initialized array, then use [`IntoIterator`].

library/core/src/iter/adapters/array_chunks.rs

@@ -1,68 +1,10 @@
+use crate::array;
 use crate::iter::{Fuse, FusedIterator, Iterator, TrustedLen};
 use crate::mem;
 use crate::mem::MaybeUninit;
 use crate::ops::{ControlFlow, Try};
 use crate::ptr;
 
-#[derive(Debug)]
-struct Remainder<T, const N: usize> {
- array: [MaybeUninit<T>; N],
- init: usize,
-}
-
-impl<T, const N: usize> Remainder<T, N> {
- fn new() -> Self {
- Self { array: MaybeUninit::uninit_array(), init: 0 }
- }
-
- unsafe fn with_init(array: [MaybeUninit<T>; N], init: usize) -> Self {
- Self { array, init }
- }
-
- fn as_slice(&self) -> &[T] {
- debug_assert!(self.init <= N);
- // SAFETY: This raw slice will only contain the initialized objects
- // within the buffer.
- unsafe {
- let slice = self.array.get_unchecked(..self.init);
- MaybeUninit::slice_assume_init_ref(slice)
- }
- }
-
- fn as_mut_slice(&mut self) -> &mut [T] {
- debug_assert!(self.init <= N);
- // SAFETY: This raw slice will only contain the initialized objects
- // within the buffer.
- unsafe {
- let slice = self.array.get_unchecked_mut(..self.init);
- MaybeUninit::slice_assume_init_mut(slice)
- }
- }
-}
-
-impl<T, const N: usize> Clone for Remainder<T, N>
-where
- T: Clone,
-{
- fn clone(&self) -> Self {
- let mut new = Self::new();
- // SAFETY: The new array is the same size and `init` is always less than
- // or equal to `N`.
- let this = unsafe { new.array.get_unchecked_mut(..self.init) };
- MaybeUninit::write_slice_cloned(this, self.as_slice());
- new.init = self.init;
- new
- }
-}
-
-impl<T, const N: usize> Drop for Remainder<T, N> {
- fn drop(&mut self) {
- // SAFETY: This raw slice will only contain the initialized objects
- // within the buffer.
- unsafe { ptr::drop_in_place(self.as_mut_slice()) }
- }
-}
-
 /// An iterator over `N` elements of the iterator at a time.
 ///
 /// The chunks do not overlap. If `N` does not divide the length of the
@@ -75,7 +17,7 @@ impl<T, const N: usize> Drop for Remainder<T, N> {
 #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "none")]
 pub struct ArrayChunks<I: Iterator, const N: usize> {
  iter: Fuse<I>,
- remainder: Remainder<I::Item, N>,
+ remainder: Option<array::IntoIter<I::Item, N>>,
 }
 
 impl<I, const N: usize> ArrayChunks<I, N>
@@ -84,25 +26,16 @@ where
 {
  pub(in crate::iter) fn new(iter: I) -> Self {
  assert!(N != 0, "chunk size must be non-zero");
- Self { iter: iter.fuse(), remainder: Remainder::new() }
- }
-
- /// Returns a reference to the remaining elements of the original iterator
- /// that are not going to be returned by this iterator. The returned slice
- /// has at most `N-1` elements.
- #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "none")]
- #[inline]
- pub fn remainder(&self) -> &[I::Item] {
- self.remainder.as_slice()
+ Self { iter: iter.fuse(), remainder: None }
  }
 
- /// Returns a mutable reference to the remaining elements of the original
- /// iterator that are not going to be returned by this iterator. The
- /// returned slice has at most `N-1` elements.
+ /// Returns an iterator over the remaining elements of the original iterator
+ /// that are not going to be returned by this iterator. The returned
+ /// iterator will yield at most `N-1` elements.
  #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "none")]
  #[inline]
- pub fn remainder_mut(&mut self) -> &mut [I::Item] {
- self.remainder.as_mut_slice()
+ pub fn into_remainder(self) -> Option<array::IntoIter<I::Item, N>> {
+ self.remainder
  }
 }
 
@@ -129,8 +62,10 @@ where
  if guard.init > 0 {
  let init = guard.init;
  mem::forget(guard);
- // SAFETY: `array` was initialized with `init` elements.
- self.remainder = unsafe { Remainder::with_init(array, init) };
+ self.remainder = {
+ // SAFETY: `array` was initialized with `init` elements.
+ Some(unsafe { array::IntoIter::with_partial(array, 0..init) })
+ };
  }
  return None;
  }
@@ -189,7 +124,7 @@ where
  let init = guard.init;
  mem::forget(guard);
  // SAFETY: `array` was initialized with `init` elements.
- self.remainder = unsafe { Remainder::with_init(array, init) };
+ self.remainder = Some(unsafe { array::IntoIter::with_partial(array, 0..init) });
  }
  R::from_output(o)
  }
@@ -370,7 +305,7 @@ where
  // SAFETY: `array` was initialized with exactly `init` elements.
  self.remainder = unsafe {
  array.get_unchecked_mut(..init).reverse();
- Remainder::with_init(array, init)
+ Some(array::IntoIter::with_partial(array, 0..init))
  };
  Some(())
  }

library/core/src/iter/traits/iterator.rs

@@ -3319,7 +3319,9 @@ pub trait Iterator {
  /// Returns an iterator over `N` elements of the iterator at a time.
  ///
  /// The chunks do not overlap. If `N` does not divide the length of the
- /// iterator, then the last up to `N-1` elements will be omitted.
+ /// iterator, then the last up to `N-1` elements will be omitted and can be
+ /// retrieved from the [`.into_remainder()`][ArrayChunks::into_remainder]
+ /// function of the iterator.
  ///
  /// # Panics
  ///
@@ -3336,7 +3338,7 @@ pub trait Iterator {
  /// assert_eq!(iter.next(), Some(['l', 'o']));
  /// assert_eq!(iter.next(), Some(['r', 'e']));
  /// assert_eq!(iter.next(), None);
- /// assert_eq!(iter.remainder(), &['m']);
+ /// assert_eq!(iter.into_remainder().unwrap().as_slice(), &['m']);
  /// ```
  ///
  /// ```

library/core/tests/iter/adapters/array_chunks.rs

@@ -15,39 +15,24 @@ fn test_iterator_array_chunks_infer() {
 fn test_iterator_array_chunks_clone_and_drop() {
  let count = Cell::new(0);
  let mut it = (0..5).map(|_| CountDrop::new(&count)).array_chunks::<3>();
-
  assert_eq!(it.by_ref().count(), 1);
  assert_eq!(count.get(), 3);
- assert_eq!(it.remainder().len(), 2);
-
  let mut it2 = it.clone();
  assert_eq!(count.get(), 3);
- assert_eq!(it2.remainder().len(), 2);
-
- drop(it);
+ assert_eq!(it.into_remainder().unwrap().len(), 2);
  assert_eq!(count.get(), 5);
- assert_eq!(it2.remainder().len(), 2);
  assert!(it2.next().is_none());
-
- drop(it2);
+ assert_eq!(it2.into_remainder().unwrap().len(), 2);
  assert_eq!(count.get(), 7);
 }
 
 #[test]
 fn test_iterator_array_chunks_remainder() {
  let mut it = (0..11).array_chunks::<4>();
- assert_eq!(it.remainder(), &[]);
- assert_eq!(it.remainder_mut(), &[]);
  assert_eq!(it.next(), Some([0, 1, 2, 3]));
- assert_eq!(it.remainder(), &[]);
- assert_eq!(it.remainder_mut(), &[]);
  assert_eq!(it.next(), Some([4, 5, 6, 7]));
- assert_eq!(it.remainder(), &[]);
- assert_eq!(it.remainder_mut(), &[]);
- assert_eq!(it.next(), None);
  assert_eq!(it.next(), None);
- assert_eq!(it.remainder(), &[8, 9, 10]);
- assert_eq!(it.remainder_mut(), &[8, 9, 10]);
+ assert_eq!(it.into_remainder().unwrap().as_slice(), &[8, 9, 10]);
 }
 
 #[test]
@@ -105,8 +90,7 @@ fn test_iterator_array_chunks_next_and_next_back() {
  assert_eq!(it.next(), None);
  assert_eq!(it.next_back(), None);
  assert_eq!(it.next(), None);
- assert_eq!(it.remainder(), &[9, 10]);
- assert_eq!(it.remainder_mut(), &[9, 10]);
+ assert_eq!(it.into_remainder().unwrap().as_slice(), &[9, 10]);
 }
 
 #[test]
@@ -119,7 +103,7 @@ fn test_iterator_array_chunks_rev_remainder() {
  assert_eq!(it.next(), None);
  assert_eq!(it.next(), None);
  }
- assert_eq!(it.remainder(), &[8, 9, 10]);
+ assert_eq!(it.into_remainder().unwrap().as_slice(), &[8, 9, 10]);
 }
 
 #[test]
@@ -128,7 +112,6 @@ fn test_iterator_array_chunks_try_fold() {
  let mut it = (0..10).map(|_| CountDrop::new(&count)).array_chunks::<3>();
  let result: Result<_, ()> = it.by_ref().try_fold(0, |acc, _item| Ok(acc + 1));
  assert_eq!(result, Ok(3));
- assert_eq!(it.remainder().len(), 1);
  assert_eq!(count.get(), 9);
  drop(it);
  assert_eq!(count.get(), 10);
@@ -137,7 +120,6 @@ fn test_iterator_array_chunks_try_fold() {
  let mut it = (0..10).map(|_| CountDrop::new(&count)).array_chunks::<3>();
  let result = it.by_ref().try_fold(0, |acc, _item| if acc < 2 { Ok(acc + 1) } else { Err(acc) });
  assert_eq!(result, Err(2));
- assert_eq!(it.remainder().len(), 0);
  assert_eq!(count.get(), 9);
  drop(it);
  assert_eq!(count.get(), 9);
@@ -166,7 +148,6 @@ fn test_iterator_array_chunks_try_rfold() {
  let mut it = (0..10).map(|_| CountDrop::new(&count)).array_chunks::<3>();
  let result: Result<_, ()> = it.try_rfold(0, |acc, _item| Ok(acc + 1));
  assert_eq!(result, Ok(3));
- assert_eq!(it.remainder().len(), 1);
  assert_eq!(count.get(), 9);
  drop(it);
  assert_eq!(count.get(), 10);