added observer to repository and updated tests

include/matador/object/object_info.hpp

@@ -2,12 +2,28 @@
 #define OBJECT_INFO_HPP
 
 #include "matador/object/basic_object_info.hpp"
+#include "matador/object/observer.hpp"
 
 #include <functional>
 
 namespace matador::object {
 class repository_node;
 
+template<typename Type>
+class observer_ptr {
+public:
+  explicit observer_ptr(std::unique_ptr<observer<Type>> &&observer)
+  : observer(std::move(observer)) {}
+
+  operator bool() const { return observer != nullptr; }
+
+  observer<Type> *get() const { return observer.get(); }
+  observer<Type> &operator*() const { return *observer; }
+  observer<Type> *operator->() const { return observer.get(); }
+
+private:
+  std::unique_ptr<observer<Type>> observer;
+};
 template<typename Type>
 class object_info final : public basic_object_info {
 public:
@@ -27,9 +43,25 @@ public:
   const Type &prototype() const { return prototype_; }
   std::unique_ptr<Type> create() const { return creator_(); }
 
+  void on_attach() const override {
+    for (auto &observer : observers_) {
+      observer->on_attach(*node_, prototype_);
+    }
+  }
+
+  void on_detach() const override {
+    for (auto &observer : observers_) {
+      observer->on_detach(*node_, prototype_);
+    }
+  }
+
+  void register_observer(observer_ptr<Type> observer) {
+    observers_.push_back(std::move(observer));
+  }
 private:
   Type prototype_;
   create_func creator_{[]{ return std::make_unique<Type>(); }};
+  std::vector<observer_ptr<Type>> observers_;
 };
 
 template<typename Type>