CODESAMPLE

Module - Go

Module Go

The Module pattern (also known as the Memento pattern) captures and externalizes an object’s internal state so that it can be restored later, providing a way to save and restore previous states without violating encapsulation. This implementation uses a State struct to hold the object’s data, and Save() and Restore() methods to manage the memento. Go’s struct composition and method receivers naturally lend themselves to this pattern. The Originator struct encapsulates the state and the logic for saving and restoring it, while the Memento struct is an immutable snapshot of the state.

package main

import "fmt"

// State holds the internal state of the Originator.
type State struct {
	Value int
}

// Memento is an immutable snapshot of the Originator's state.
type Memento struct {
	State State
}

// Originator creates and manages its own state.
type Originator struct {
	currentState State
}

// NewOriginator creates a new Originator with an initial state.
func NewOriginator(initialValue int) *Originator {
	return &Originator{State{Value: initialValue}}
}

// SetValue changes the Originator's state.
func (o *Originator) SetValue(newValue int) {
	o.currentState.Value = newValue
}

// Value returns the current value of the originator.
func (o *Originator) Value() int {
	return o.currentState.Value
}

// Save creates a memento containing the current state.
func (o *Originator) Save() *Memento {
	return &Memento{State{Value: o.currentState.Value}}
}

// Restore sets the Originator's state to the one stored in the memento.
func (o *Originator) Restore(memento *Memento) {
	o.currentState = memento.State
}

func main() {
	originator := NewOriginator(10)
	fmt.Println("Initial value:", originator.Value())

	memento := originator.Save()

	originator.SetValue(20)
	fmt.Println("Value after change:", originator.Value())

	originator.Restore(memento)
	fmt.Println("Value after restore:", originator.Value())
}