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Memento in Go
Memento is a behavioral design pattern that allows making snapshots of an object’s state and restoring it in future.
The Memento doesn’t compromise the internal structure of the object it works with, as well as data kept inside the snapshots.
Conceptual Example
The Memento pattern lets us save snapshots for an object’s state. You can use these snapshots to revert the object to the previous state. It’s handy when you need to implement undo-redo operations on an object.
originator.go: Originator
package main
type originator struct {
state string
}
func (e *originator) createMemento() *memento {
return &memento{state: e.state}
}
func (e *originator) restoreMemento(m *memento) {
e.state = m.getSavedState()
}
func (e *originator) setState(state string) {
e.state = state
}
func (e *originator) getState() string {
return e.state
}
memento.go: Memento
package main
type memento struct {
state string
}
func (m *memento) getSavedState() string {
return m.state
}
caretaker.go: Caretaker
package main
type caretaker struct {
mementoArray []*memento
}
func (c *caretaker) addMemento(m *memento) {
c.mementoArray = append(c.mementoArray, m)
}
func (c *caretaker) getMemento(index int) *memento {
return c.mementoArray[index]
}
main.go: Client code
package main
import "fmt"
func main() {
caretaker := &caretaker{
mementoArray: make([]*memento, 0),
}
originator := &originator{
state: "A",
}
fmt.Printf("Originator Current State: %s\n", originator.getState())
caretaker.addMemento(originator.createMemento())
originator.setState("B")
fmt.Printf("Originator Current State: %s\n", originator.getState())
caretaker.addMemento(originator.createMemento())
originator.setState("C")
fmt.Printf("Originator Current State: %s\n", originator.getState())
caretaker.addMemento(originator.createMemento())
originator.restoreMemento(caretaker.getMemento(1))
fmt.Printf("Restored to State: %s\n", originator.getState())
originator.restoreMemento(caretaker.getMemento(0))
fmt.Printf("Restored to State: %s\n", originator.getState())
}
output.txt: Execution result
originator Current State: A
originator Current State: B
originator Current State: C
Restored to State: B
Restored to State: A
Based on: Golang By Example
