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Go 备忘录模式讲解和代码示例

备忘录是一种行为设计模式， 允许生成对象状态的快照并在以后将其还原。

备忘录不会影响它所处理的对象的内部结构， 也不会影响快照中保存的数据。

** 进一步了解备忘录模式 **

概念示例

备忘录模式让我们可以保存对象状态的快照。 你可使用这些快照来将对象恢复到之前的状态。 这在需要在对象上实现撤销-重做操作时非常实用。

** originator.go:  原发器

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:  备忘录

package main

type Memento struct {
    state string
}

func (m *Memento) getSavedState() string {
    return m.state
}

** caretaker.go:  负责人

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:  客户端代码

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:  执行结果

originator Current State: A
originator Current State: B
originator Current State: C
Restored to State: B
Restored to State: A