@@ -135,13 +135,24 @@ impl<'a, T> Iter<'a, T> {
135135 // SAFETY: the type invariant guarantees the pointer represents a valid reference
136136 unsafe { p. as_ref ( ) }
137137 }
138+ }
138139
139- fn empty ( ) -> Self {
140+ #[ allow( unused_lifetimes) ]
141+ #[ stable( feature = "default_iters" , since = "1.70.0" ) ]
142+ impl < T > Default for Iter < ' _ , T > {
143+ /// Creates an empty slice iterator.
144+ ///
145+ /// ```
146+ /// # use core::slice::Iter;
147+ /// let iter: Iter<'_, u8> = Default::default();
148+ /// assert_eq!(iter.len(), 0);
149+ /// ```
150+ fn default ( ) -> Self {
140151 ( & [ ] ) . into_iter ( )
141152 }
142153}
143154
144- iterator ! { struct Iter - > * const T , & ' a T , {
155+ iterator ! { struct Iter < ' a , T > = > * const T , & ' a T , {
145156 fn is_sorted_by<F >( self , mut compare: F ) -> bool
146157 where
147158 Self : Sized ,
@@ -365,8 +376,19 @@ impl<'a, T> IterMut<'a, T> {
365376 // SAFETY: the type invariant guarantees the pointer represents a valid item
366377 unsafe { p. as_mut ( ) }
367378 }
379+ }
368380
369- fn empty ( ) -> Self {
381+ #[ allow( unused_lifetimes) ]
382+ #[ stable( feature = "default_iters" , since = "1.70.0" ) ]
383+ impl < T > Default for IterMut < ' _ , T > {
384+ /// Creates an empty slice iterator.
385+ ///
386+ /// ```
387+ /// # use core::slice::IterMut;
388+ /// let iter: IterMut<'_, u8> = Default::default();
389+ /// assert_eq!(iter.len(), 0);
390+ /// ```
391+ fn default ( ) -> Self {
370392 ( & mut [ ] ) . into_iter ( )
371393 }
372394}
@@ -386,7 +408,83 @@ impl<T> AsRef<[T]> for IterMut<'_, T> {
386408// }
387409// }
388410
389- iterator ! { struct IterMut -> * mut T , & ' a mut T , { } }
411+ iterator ! { struct IterMut <' a, T > => * mut T , & ' a mut T , { } }
412+
413+ /// Iterator over all the `NonNull<T>` pointers to the elements of a slice.
414+ #[ unstable( feature = "slice_non_null_iter" , issue = "none" ) ]
415+ #[ must_use = "iterators are lazy and do nothing unless consumed" ]
416+ pub struct NonNullIter < T > {
417+ /// The pointer to the next element to return, or the past-the-end location
418+ /// if the iterator is empty.
419+ ///
420+ /// This address will be used for all ZST elements, never changed.
421+ ptr : NonNull < T > ,
422+ /// For non-ZSTs, the non-null pointer to the past-the-end element.
423+ ///
424+ /// For ZSTs, this is `ptr::without_provenance_mut(len)`.
425+ end_or_len : * const T ,
426+ }
427+
428+ #[ unstable( feature = "slice_non_null_iter" , issue = "none" ) ]
429+ impl < T : fmt:: Debug > fmt:: Debug for NonNullIter < T > {
430+ fn fmt ( & self , f : & mut fmt:: Formatter < ' _ > ) -> fmt:: Result {
431+ f. debug_tuple ( "NonNullIter" ) . field ( & self . make_shortlived_slice ( ) ) . finish ( )
432+ }
433+ }
434+
435+ impl < T > NonNullIter < T > {
436+ /// Turn an iterator giving `&T`s into one giving `NonNull<T>`s.
437+ #[ unstable( feature = "slice_non_null_iter" , issue = "none" ) ]
438+ pub fn from_slice_iter ( Iter { ptr, end_or_len, .. } : Iter < ' _ , T > ) -> Self {
439+ Self { ptr, end_or_len }
440+ }
441+
442+ /// Turn an iterator giving `&mut T`s into one giving `NonNull<T>`s.
443+ #[ unstable( feature = "slice_non_null_iter" , issue = "none" ) ]
444+ pub fn from_slice_iter_mut ( IterMut { ptr, end_or_len, .. } : IterMut < ' _ , T > ) -> Self {
445+ Self { ptr, end_or_len }
446+ }
447+
448+ /// Creates a new iterator over the `len` items starting at `ptr`
449+ ///
450+ /// # Safety
451+ ///
452+ /// `ptr` through `ptr.add(len)` must be a single allocated object
453+ /// such that that
454+ #[ unstable( feature = "slice_non_null_iter" , issue = "none" ) ]
455+ #[ inline]
456+ pub unsafe fn from_parts ( ptr : NonNull < T > , len : usize ) -> Self {
457+ // SAFETY: There are several things here:
458+ //
459+ // `ptr` has been obtained by `slice.as_ptr()` where `slice` is a valid
460+ // reference thus it is non-NUL and safe to use and pass to
461+ // `NonNull::new_unchecked` .
462+ //
463+ // Adding `slice.len()` to the starting pointer gives a pointer
464+ // at the end of `slice`. `end` will never be dereferenced, only checked
465+ // for direct pointer equality with `ptr` to check if the iterator is
466+ // done.
467+ //
468+ // In the case of a ZST, the end pointer is just the length. It's never
469+ // used as a pointer at all, and thus it's fine to have no provenance.
470+ //
471+ // See the `next_unchecked!` and `is_empty!` macros as well as the
472+ // `post_inc_start` method for more information.
473+ unsafe {
474+ let end_or_len =
475+ if T :: IS_ZST { without_provenance_mut ( len) } else { ptr. as_ptr ( ) . add ( len) } ;
476+
477+ Self { ptr, end_or_len }
478+ }
479+ }
480+
481+ #[ inline]
482+ unsafe fn non_null_to_item ( p : NonNull < T > ) -> <Self as Iterator >:: Item {
483+ p
484+ }
485+ }
486+
487+ iterator ! { struct NonNullIter <T > => * const T , NonNull <T >, { } }
390488
391489/// An internal abstraction over the splitting iterators, so that
392490/// splitn, splitn_mut etc can be implemented once.
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