add m_key

src/layer/layer.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <string>
 #include "event/event.hpp"
 #include "utils/using.hpp"
 
@@ -23,6 +24,7 @@ namespace VE
 
     protected:
       event_fn<event> execute;
+      std::string m_key;
   };
 }