added singleton pattern

creational/main.go

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/jianhan/go-patterns/creational/singleton"
+)
+
+func main() {
+	instance := singleton.GetInstance()
+	fmt.Println(instance.AddOne())
+}

creational/singleton/singleton.go

@@ -0,0 +1,23 @@
+package singleton
+
+type Singleton interface {
+	AddOne() int
+}
+
+type singleton struct {
+	count int
+}
+
+func (s *singleton) AddOne() int {
+	s.count++
+	return s.count
+}
+
+var instance *singleton
+
+func GetInstance() Singleton {
+	if instance == nil {
+		instance = new(singleton)
+	}
+	return instance
+}