vault backup: 2025-01-17 17:10:15

5 Media/8 Courses/Design Patterns by Construx.md

@@ -338,9 +338,27 @@ Forces:
 
 > [!Note] Implementation Notes
 > - same notification interface for all observers on same subject (even if information needs are different)
+> - update() might carry new the updated data, or its just a ping and the observer needs to pull upon the notification
+> - no control over the order
+> - subject may need prevent modification of state until all observers were notified
+> - implementation is an interface and not a base class
 
+Observer design patterns are often used with model-view-controller architectures
+![[Pasted image 20250117162946.png]]
 
+Variation on the theme: Event Channel: many publishers and many subscribers
 #### Design Principles
+- high cohesion / loose coupling
+- design to invariants / design for change
+- encapsulation
+
+
+
+> [!NOTE] Key Points
+> - pattern allows to notify many others when state changes
+> - decoupling of information provider from information consumers
+> - state data can be pushed on update() or pulled by observers
+> - event channels (variant) supports many publishers and many subscribers on the same channel
 
 ### Template Method