Short-circuits op-assignment for indexing and dotting.

src/fn_call.rs

@@ -287,6 +287,11 @@ impl Engine {
 
         // See if it is built in.
         if args.len() == 2 {
+            match run_builtin_binary_op(fn_name, args[0], args[1])? {
+                Some(v) => return Ok((v, false)),
+                None => (),
+            }
+
             if is_ref {
                 let (first, second) = args.split_first_mut().unwrap();
 
@@ -295,11 +300,6 @@ impl Engine {
                     None => (),
                 }
             }
-
-            match run_builtin_binary_op(fn_name, args[0], args[1])? {
-                Some(v) => return Ok((v, false)),
-                None => (),
-            }
         }
 
         // Return default value (if any)