feat: new post on observer pattern

content/posts/design-patterns-observer-pattern.mdx

@@ -0,0 +1,60 @@
+---
+published: true
+title: "Observer pattern - Design Patterns"
+excerpt: "The observer pattern is a behavioural pattern."
+category: "Programming"
+tags: ["oop", "programming", "design-patterns"]
+date: "2024-10-23T07:35:00.322Z"
+author:
+name: "M Ferreira"
+picture: "https://res.cloudinary.com/mannuel/image/upload/f_auto/v1604067445/images/mee.jpg"
+ogImage:
+  url: "https://res.cloudinary.com/mannuel/image/upload/v1729574243/mfcom/uvqa1m0nuuoahqii7mof.png"
+coverImage: "https://res.cloudinary.com/mannuel/image/upload/v1729574243/mfcom/uvqa1m0nuuoahqii7mof.png"
+---
+
+## Pattern type
+
+This is a behavioural pattern that allows a one-to-many relationship between objects so that when the state of one object changes all its children objects are notified and updated automatically.
+
+## Intent
+
+The pattern intent is to make it easier to maintain consistency between related objects without making them tightly coupled.
+
+## Problem
+
+...
+
+## Pattern
+
+```mermaid
+classDiagram
+    class Observer {
+        +calculateTotal()
+        +calulateShipping()
+    }
+
+```
+
+## Code example
+
+````python
+class Subject:
+    def __init__(self):
+        pass
+
+```python
+class Observer:
+    def __init__(self):
+        pass
+````
+
+```python
+...
+```
+
+prints out:
+
+```text
+...
+```