wip nth_back on chunks

[rust.git] / src / libcore / slice / mod.rs

diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index bf3dda48dc797521c6407104262897d0276a763f..54c5285bc495cdeb830f6310eacefe9f7feca250 100644 (file)
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -1,3 +1,5 @@
+// ignore-tidy-filelength
+
 //! Slice management and manipulation.
 //!
 //! For more details see [`std::slice`].
@@ -357,6 +359,10 @@ pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
     /// The caller must ensure that the slice outlives the pointer this
     /// function returns, or else it will end up pointing to garbage.
     ///
+    /// The caller must also ensure that the memory the pointer (non-transitively) points to
+    /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
+    /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
+    ///
     /// Modifying the container referenced by this slice may cause its buffer
     /// to be reallocated, which would also make any pointers to it invalid.
     ///
@@ -372,6 +378,8 @@ pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
     ///     }
     /// }
     /// ```
+    ///
+    /// [`as_mut_ptr`]: #method.as_mut_ptr
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub const fn as_ptr(&self) -> *const T {
@@ -3539,6 +3547,11 @@ fn size_hint(&self) -> (usize, Option<usize>) {
             (1, Some(self.v.len() + 1))
         }
     }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -3637,6 +3650,11 @@ fn size_hint(&self) -> (usize, Option<usize>) {
             (1, Some(self.v.len() + 1))
         }
     }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -3702,6 +3720,11 @@ fn next(&mut self) -> Option<&'a [T]> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.inner.size_hint()
     }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
 }
 
 #[stable(feature = "slice_rsplit", since = "1.27.0")]
@@ -3766,6 +3789,11 @@ fn next(&mut self) -> Option<&'a mut [T]> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.inner.size_hint()
     }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
 }
 
 #[stable(feature = "slice_rsplit", since = "1.27.0")]
@@ -4150,6 +4178,22 @@ fn next_back(&mut self) -> Option<&'a [T]> {
             Some(snd)
         }
     }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) {
+        let (end, overflow) = self.v.len().overflowing_sub(n);
+        if end < self.v.len()  || overflow {
+            self.v = &[];
+            None
+        } else {
+            let start = match end.checked_sub(self.chunk_size) {
+                Some(sum) => cmp::min(self.v.len(), sum),
+                None => self.v.len(),
+            };
+            let nth = &self.v[start..end];
+            self.v = &self.v[end..];
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]