Add array_windows fn

library/alloc/src/lib.rs

@@ -76,6 +76,7 @@
 #![cfg_attr(test, feature(test))]
 #![feature(allocator_api)]
 #![feature(array_chunks)]
+#![feature(array_windows)]
 #![feature(allow_internal_unstable)]
 #![feature(arbitrary_self_types)]
 #![feature(box_patterns)]

library/alloc/src/slice.rs

@@ -95,6 +95,8 @@ use crate::vec::Vec;
 pub use core::slice::ArrayChunks;
 #[unstable(feature = "array_chunks", issue = "74985")]
 pub use core::slice::ArrayChunksMut;
+#[unstable(feature = "array_windows", issue = "75027")]
+pub use core::slice::ArrayWindows;
 #[stable(feature = "slice_get_slice", since = "1.28.0")]
 pub use core::slice::SliceIndex;
 #[stable(feature = "from_ref", since = "1.28.0")]

library/core/src/slice/iter.rs

@@ -1687,6 +1687,106 @@ unsafe impl<'a, T> TrustedRandomAccess for ChunksExactMut<'a, T> {
  }
 }
 
+/// A windowed iterator over a slice in overlapping chunks (`N` elements at a
+/// time), starting at the beginning of the slice
+///
+/// This struct is created by the [`array_windows`] method on [slices].
+///
+/// [`array_windows`]: ../../std/primitive.slice.html#method.array_windows
+/// [slices]: ../../std/primitive.slice.html
+#[derive(Debug, Clone, Copy)]
+#[unstable(feature = "array_windows", issue = "75027")]
+pub struct ArrayWindows<'a, T: 'a, const N: usize> {
+ pub(crate) slice_head: *const T,
+ pub(crate) num: usize,
+ pub(crate) marker: marker::PhantomData<&'a [T; N]>,
+}
+
+#[unstable(feature = "array_windows", issue = "75027")]
+impl<'a, T, const N: usize> Iterator for ArrayWindows<'a, T, N> {
+ type Item = &'a [T; N];
+
+ #[inline]
+ fn next(&mut self) -> Option<Self::Item> {
+ if self.num == 0 {
+ return None;
+ }
+ // SAFETY:
+ // This is safe because it's indexing into a slice guaranteed to be length > N.
+ let ret = unsafe { &*self.slice_head.cast::<[T; N]>() };
+ // SAFETY: Guaranteed that there are at least 1 item remaining otherwise
+ // earlier branch would've been hit
+ self.slice_head = unsafe { self.slice_head.add(1) };
+
+ self.num -= 1;
+ Some(ret)
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (self.num, Some(self.num))
+ }
+
+ #[inline]
+ fn count(self) -> usize {
+ self.num
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Option<Self::Item> {
+ if self.num <= n {
+ self.num = 0;
+ return None;
+ }
+ // SAFETY:
+ // This is safe because it's indexing into a slice guaranteed to be length > N.
+ let ret = unsafe { &*self.slice_head.add(n).cast::<[T; N]>() };
+ // SAFETY: Guaranteed that there are at least n items remaining
+ self.slice_head = unsafe { self.slice_head.add(n + 1) };
+
+ self.num -= n + 1;
+ Some(ret)
+ }
+
+ #[inline]
+ fn last(mut self) -> Option<Self::Item> {
+ self.nth(self.num.checked_sub(1)?)
+ }
+}
+
+#[unstable(feature = "array_windows", issue = "75027")]
+impl<'a, T, const N: usize> DoubleEndedIterator for ArrayWindows<'a, T, N> {
+ #[inline]
+ fn next_back(&mut self) -> Option<&'a [T; N]> {
+ if self.num == 0 {
+ return None;
+ }
+ // SAFETY: Guaranteed that there are n items remaining, n-1 for 0-indexing.
+ let ret = unsafe { &*self.slice_head.add(self.num - 1).cast::<[T; N]>() };
+ self.num -= 1;
+ Some(ret)
+ }
+
+ #[inline]
+ fn nth_back(&mut self, n: usize) -> Option<&'a [T; N]> {
+ if self.num <= n {
+ self.num = 0;
+ return None;
+ }
+ // SAFETY: Guaranteed that there are n items remaining, n-1 for 0-indexing.
+ let ret = unsafe { &*self.slice_head.add(self.num - (n + 1)).cast::<[T; N]>() };
+ self.num -= n + 1;
+ Some(ret)
+ }
+}
+
+#[unstable(feature = "array_windows", issue = "75027")]
+impl<T, const N: usize> ExactSizeIterator for ArrayWindows<'_, T, N> {
+ fn is_empty(&self) -> bool {
+ self.num == 0
+ }
+}
+
 /// An iterator over a slice in (non-overlapping) chunks (`N` elements at a
 /// time), starting at the beginning of the slice.
 ///

library/core/src/slice/mod.rs

@@ -56,6 +56,9 @@ pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
 #[unstable(feature = "array_chunks", issue = "74985")]
 pub use iter::{ArrayChunks, ArrayChunksMut};
 
+#[unstable(feature = "array_windows", issue = "75027")]
+pub use iter::ArrayWindows;
+
 #[unstable(feature = "split_inclusive", issue = "72360")]
 pub use iter::{SplitInclusive, SplitInclusiveMut};
 
@@ -1099,6 +1102,40 @@ impl<T> [T] {
  }
  }
 
+ /// Returns an iterator over overlapping windows of `N` elements of a slice,
+ /// starting at the beginning of the slice.
+ ///
+ /// This is the const generic equivalent of [`windows`].
+ ///
+ /// If `N` is smaller than the size of the array, it will return no windows.
+ ///
+ /// # Panics
+ ///
+ /// Panics if `N` is 0. This check will most probably get changed to a compile time
+ /// error before this method gets stabilized.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(array_windows)]
+ /// let slice = [0, 1, 2, 3];
+ /// let mut iter = slice.array_windows();
+ /// assert_eq!(iter.next().unwrap(), &[0, 1]);
+ /// assert_eq!(iter.next().unwrap(), &[1, 2]);
+ /// assert_eq!(iter.next().unwrap(), &[2, 3]);
+ /// assert!(iter.next().is_none());
+ /// ```
+ ///
+ /// [`windows`]: #method.windows
+ #[unstable(feature = "array_windows", issue = "75027")]
+ #[inline]
+ pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
+ assert_ne!(N, 0);
+
+ let num_windows = self.len().saturating_sub(N - 1);
+ ArrayWindows { slice_head: self.as_ptr(), num: num_windows, marker: marker::PhantomData }
+ }
+
  /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
  /// of the slice.
  ///

library/core/tests/lib.rs

@@ -2,6 +2,7 @@
 #![feature(array_chunks)]
 #![feature(array_methods)]
 #![feature(array_map)]
+#![feature(array_windows)]
 #![feature(bool_to_option)]
 #![feature(bound_cloned)]
 #![feature(box_syntax)]

library/core/tests/slice.rs

@@ -657,6 +657,55 @@ fn test_array_chunks_mut_zip() {
  assert_eq!(v1, [13, 14, 19, 20, 4]);
 }
 
+#[test]
+fn test_array_windows_infer() {
+ let v: &[i32] = &[0, 1, 0, 1];
+ assert_eq!(v.array_windows::<2>().count(), 3);
+ let c = v.array_windows();
+ for &[a, b] in c {
+ assert_eq!(a + b, 1);
+ }
+
+ let v2: &[i32] = &[0, 1, 2, 3, 4, 5, 6];
+ let total = v2.array_windows().map(|&[a, b, c]| a + b + c).sum::<i32>();
+ assert_eq!(total, 3 + 6 + 9 + 12 + 15);
+}
+
+#[test]
+fn test_array_windows_count() {
+ let v: &[i32] = &[0, 1, 2, 3, 4, 5];
+ let c = v.array_windows::<3>();
+ assert_eq!(c.count(), 4);
+
+ let v2: &[i32] = &[0, 1, 2, 3, 4];
+ let c2 = v2.array_windows::<6>();
+ assert_eq!(c2.count(), 0);
+
+ let v3: &[i32] = &[];
+ let c3 = v3.array_windows::<2>();
+ assert_eq!(c3.count(), 0);
+}
+
+#[test]
+fn test_array_windows_nth() {
+ let v: &[i32] = &[0, 1, 2, 3, 4, 5];
+ let snd = v.array_windows::<4>().nth(1);
+ assert_eq!(snd, Some(&[1, 2, 3, 4]));
+ let mut arr_windows = v.array_windows::<2>();
+ assert_ne!(arr_windows.nth(0), arr_windows.nth(0));
+ let last = v.array_windows::<3>().last();
+ assert_eq!(last, Some(&[3, 4, 5]));
+}
+
+#[test]
+fn test_array_windows_nth_back() {
+ let v: &[i32] = &[0, 1, 2, 3, 4, 5];
+ let snd = v.array_windows::<4>().nth_back(1);
+ assert_eq!(snd, Some(&[1, 2, 3, 4]));
+ let mut arr_windows = v.array_windows::<2>();
+ assert_ne!(arr_windows.nth_back(0), arr_windows.nth_back(0));
+}
+
 #[test]
 fn test_rchunks_count() {
  let v: &[i32] = &[0, 1, 2, 3, 4, 5];

src/test/ui/const-generics/type-dependent/issue-61936.rs

@@ -5,21 +5,21 @@
 #![cfg_attr(min, feature(min_const_generics))]
 
 trait SliceExt<T: Clone> {
- fn array_windows<'a, const N: usize>(&'a self) -> ArrayWindows<'a, T, N>;
+ fn array_windows_example<'a, const N: usize>(&'a self) -> ArrayWindowsExample<'a, T, N>;
 }
 
 impl <T: Clone> SliceExt<T> for [T] {
- fn array_windows<'a, const N: usize>(&'a self) -> ArrayWindows<'a, T, N> {
- ArrayWindows{ idx: 0, slice: &self }
+ fn array_windows_example<'a, const N: usize>(&'a self) -> ArrayWindowsExample<'a, T, N> {
+ ArrayWindowsExample{ idx: 0, slice: &self }
  }
 }
 
-struct ArrayWindows<'a, T, const N: usize> {
+struct ArrayWindowsExample<'a, T, const N: usize> {
  slice: &'a [T],
  idx: usize,
 }
 
-impl <'a, T: Clone, const N: usize> Iterator for ArrayWindows<'a, T, N> {
+impl <'a, T: Clone, const N: usize> Iterator for ArrayWindowsExample<'a, T, N> {
  type Item = [T; N];
  fn next(&mut self) -> Option<Self::Item> {
  // Note: this is unsound for some `T` and not meant as an example
@@ -45,7 +45,7 @@ const FOUR: usize = 4;
 fn main() {
  let v: Vec<usize> = vec![0; 100];
 
- for array in v.as_slice().array_windows::<FOUR>() {
+ for array in v.as_slice().array_windows_example::<FOUR>() {
  assert_eq!(array, [0, 0, 0, 0])
  }
 }