feat add dispatcher to sled.h

src/sled/experimental/design_patterns/dispatcher.h

@@ -4,6 +4,7 @@
 #include "sled/synchronization/mutex.h"
 #include <memory>
 #include <set>
+#include <type_traits>
 
 namespace sled {
 namespace experimental {
@@ -11,12 +12,13 @@ namespace experimental {
 template<typename T>
 class Dispatcher {
 public:
+    static_assert(!std::is_rvalue_reference<T>::value, "must be a value type");
     enum class DispatchResult { kHandled, kNotFound };
 
     struct Handler {
         virtual ~Handler()                    = default;
         virtual bool HandleMessage(const T &) = 0;
-        virtual bool OnMessage(T &&)          = 0;
+        virtual bool OnMessage(const T &)     = 0;
     };
 
     virtual ~Dispatcher() = default;

src/sled/sled.h

@@ -9,6 +9,9 @@ namespace async {}
 #include "inja.hpp"
 #include "rx.h"
 
+// experimental
+#include "sled/experimental/design_patterns/dispatcher.h"
+
 // event_bus
 #include "sled/event_bus/event_bus.h"