implemented memento pattern

behavioral/memento/memento.go

@@ -0,0 +1,39 @@
+package memento
+
+import (
+	"errors"
+)
+
+type State struct {
+	Description string
+}
+
+type memento struct {
+	state State
+}
+
+type originator struct {
+	state State
+}
+func (o *originator) StoreStateToMemento() memento {
+	return memento{state: o.state}
+}
+func (o *originator) StoreStateFromMemento(m memento) {
+	o.state = m.state
+}
+
+type careTaker struct {
+	mementos []memento
+}
+func (c *careTaker) Push(m memento)  {
+	c.mementos = append(c.mementos, m)
+
+}
+func (c *careTaker) Get(i int) (memento, error)  {
+	var m memento
+	if len(c.mementos) < i || i< 0 {
+		return m, errors.New("Index is out of range")
+	}
+	
+	return c.mementos[i], nil
+}