add missing '&' causing temporary value to be modified

diff --git a/src/plugins/operation.cpp b/src/plugins/operation.cpp
index 28b186d..68977c4 100644 (file)
--- a/src/plugins/operation.cpp
+++ b/src/plugins/operation.cpp
@@ -86,7 +86,7 @@ void Operation::receive(Operation* source)
         break;
       }
     if (enough_tokens) {
-      for (auto [key, val] : predecessors_)
+      for (auto& [key, val] : predecessors_)
         val--;
       enqueue_execs(1);
     }