implemented observer pattern

README.md

@@ -1,6 +1,6 @@
-![alt text][gooopher]
+<img src="logo.png" alt="design patterns logo" align="center" />
-
+<br />
-[gooopher]:https://raw.githubusercontent.com/ismayilmalik/golang-design-patterns/master/gopher.jpg "Gooopher.."
+<br />
 
 # Design patterns in golang
 >A beginner guide... happy coding!
@@ -20,6 +20,7 @@
 - [Behavioral patterns](#behavioral-patterns)
     - [Chain of responsibility](#chain-of-responsibility)
     - [Strategy](#strategy)
+    - [Observer](#observer)
 - [Concurrency patterns](#concurrency-patterns)
 
 ---
@@ -78,5 +79,8 @@ request along the chain until an object handles it.
 Define a family oafl gorit h ms, encapsulate each one, and make them interchangeable.
 Strategy lets the algorithm vary independently from clients that use it.
 
+### Observer
+Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically
+
 ## Concurrency patterns
 Pattenrs for concurrent work and parallel execution in Go.

behavioral/observer/observer.go

@@ -0,0 +1,38 @@
+package observer
+
+import (
+	"fmt"
+)
+
+type Observer interface {
+	Notify(string)
+}
+
+type Publisher struct {
+	ObserverList []Observer
+}
+
+func (p *Publisher) Subscribe(o Observer) {
+	p.ObserverList = append(p.ObserverList, o)
+}
+
+func (p *Publisher) Unsubscribe(o Observer) {
+	var index int
+	for i, v := range p.ObserverList {
+		if v == o {
+			index = i
+			break
+		}
+	}
+
+	p.ObserverList = append(p.ObserverList[:index], p.ObserverList[index + 1:]...)
+}
+
+func (p *Publisher) Publish(m string) {
+	fmt.Println("Got new message! Publishing...")
+	for _, o := range p.ObserverList {
+		o.Notify(m)
+	}
+	fmt.Println("Puplished!")
+}
+