dlist_arc: cursor support

ghostcell/src/dlist_arc.rs

@@ -116,6 +116,16 @@ impl<'id, T> Node<'id, T> {
             cur = node.next.as_deref();
         }
     }
+
+    pub fn cursor_mut<'curs>(
+        node: NodePtr<'id, T>,
+        token: &'curs mut GhostToken<'id>,
+    ) -> CursorMut<'id, 'curs, T> {
+        CursorMut {
+            cur: Some(node),
+            token,
+        }
+    }
 }
 
 /// An immutable iterator.
@@ -142,3 +152,28 @@ where
         }
     }
 }
+
+pub struct CursorMut<'id, 'curs, T> {
+    cur: Option<NodePtr<'id, T>>,
+    token: &'curs mut GhostToken<'id>,
+}
+
+impl <'id, 'curs, T> CursorMut<'id, 'curs, T> {
+    pub fn current(&mut self) -> Option<&mut T> {
+        if let Some(ref mut node) = self.cur {
+            Some(&mut node.borrow_mut(self.token).data)
+        } else {
+            None
+        }
+    }
+
+    pub fn move_next(&mut self) -> Result<(), ()> {
+        if let Some(ref mut node) = self.cur {
+            let next = node.borrow(self.token).next.clone();
+            self.cur = next;
+            Ok(())
+        } else {
+            Err(())
+        }
+    }
+}