collections: Use IterMut to indicate mutable borrow

This way we don't need PhantomData

Author: Ulrik Sverdrup

src/libcollections/vec.rs

@@ -765,14 +765,16 @@ impl<T> Vec<T> {
         unsafe {
             // set self.vec length's to start, to be safe in case Drain is leaked
             self.set_len(start);
-            let range_slice = slice::from_raw_parts(self.as_ptr().offset(start as isize),
-                                                    end - start);
+            // Use the borrow in the IterMut to indicate borrowing behavior of the
+            // whole Drain iterator (like &mut T).
+            let range_slice = slice::from_raw_parts_mut(
+                                        self.as_mut_ptr().offset(start as isize),
+                                        end - start);
             Drain {
                 tail_start: end,
                 tail_len: len - end,
-                iter: range_slice.iter(),
+                iter: range_slice.iter_mut(),
                 vec: self as *mut _,
-                _marker: PhantomData,
             }
         }
     }
@@ -1832,9 +1834,8 @@ pub struct Drain<'a, T: 'a> {
     /// Length of tail
     tail_len: usize,
     /// Current remaining range to remove
-    iter: slice::Iter<'a, T>,
+    iter: slice::IterMut<'a, T>,
     vec: *mut Vec<T>,
-    _marker: PhantomData<&'a mut Vec<T>>,
 }
 
 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}