Fix ArenaVector::swap (#7115)

This was never right for over a decade, and just never used I suppose... it should
have been called "take" since it grabbed data from the other item and then set
that other item to empty. Fix it so it swaps properly.

1 files changed, 3 insertions, 6 deletions

diff --git a/src/mixed_arena.h b/src/mixed_arena.h
index 530fa9daa..057887b82 100644
--- a/src/mixed_arena.h
+++ b/src/mixed_arena.h
@@ -263,12 +263,9 @@ public:
   void operator=(SubType& other) { set(other); }
 
   void swap(SubType& other) {
-    data = other.data;
-    usedElements = other.usedElements;
-    allocatedElements = other.allocatedElements;
-
-    other.data = nullptr;
-    other.usedElements = other.allocatedElements = 0;
+    std::swap(data, other.data);
+    std::swap(usedElements, other.usedElements);
+    std::swap(allocatedElements, other.allocatedElements);
   }
 
   // iteration