Command 命令模式:

將訊息封裝成物件, 以便能用各種不同訊息, 暫佇, 紀律, 復原等方式加以參數化處理

將一個請求封裝為一個物件, 讓你可以用不同的請求對客戶進行參數化; 對請求排隊或紀錄請求日誌, 以及支援可取消的操作

不要為程式碼加上基於猜測的, 實際上不需要的功能. 如果不清楚一個系統是否需要命令模式, 就不要急著實現它. 事實上, 在需要的時候透過重構實現這個模式並不難, 只有在真正需要如取消/恢復等功能時, 把原本的程式碼重構為命令模式才有意義

Example

https://github.com/kimi0230/DesignPatternGolang/tree/master/Command

package command

import (
    "fmt"
    "time"
)

// Waiter : Invoker
type Waiter struct {
    orders []Command
}

func (w *Waiter) SetOrder(c Command) {
    if w == nil {
        return
    }
    w.orders = append(w.orders, c)
    fmt.Printf("增加訂單: %s, 時間: %s \n", c.ToString(), time.Now().UTC().String())
}

func (w *Waiter) CancelOrder(c Command) {
    if w == nil {
        return
    }
    for i := 0; i < len(w.orders); i++ {
        if w.orders[i] == c {
            w.orders = removeCommand(w.orders, i)
            break
        }
    }
    fmt.Printf("刪除訂單: %s, 時間: %s \n", c.ToString(), time.Now().UTC().String())
}
func removeCommand(slice []Command, s int) []Command {
    slice[s] = nil
    return append(slice[:s], slice[s+1:]...)
}
func (w *Waiter) Notify() {
    for _, cmd := range w.orders {
        cmd.Execute()
    }
}

// Command : Command
type Command interface {
    ToString() string
    Execute()
}

// BakeMuttonCommand : 烤羊肉命令 ConcreteCommand
type BakeMuttonCommand struct {
    name     string
    receiver Barbecuer
}

func NewBakeMuttonCommand(name string) *BakeMuttonCommand {
    return &BakeMuttonCommand{name, Barbecuer{}}
}
func (c *BakeMuttonCommand) SetReceiver(r Barbecuer) {
    if c == nil {
        return
    }
    c.receiver = r
}
func (c *BakeMuttonCommand) ToString() string {
    if c == nil {
        return ""
    }
    return c.name
}
func (c *BakeMuttonCommand) Execute() {
    c.receiver.BakeMutton()
}

// BakeChickenWingCommand : 烤雞翅命令 ConcreteCommand
type BakeChickenWingCommand struct {
    name     string
    receiver Barbecuer
}

func NewBakeChickenWingCommand(name string) *BakeChickenWingCommand {
    return &BakeChickenWingCommand{name, Barbecuer{}}
}
func (c *BakeChickenWingCommand) SetReceiver(r Barbecuer) {
    if c == nil {
        return
    }
    c.receiver = r
}
func (c *BakeChickenWingCommand) ToString() string {
    if c == nil {
        return ""
    }
    return c.name
}
func (c *BakeChickenWingCommand) Execute() {
    c.receiver.BakeChickenWing()
}

// Barbecuer :烤肉串者 Receiver
type Barbecuer struct{}

func (r *Barbecuer) BakeMutton() {
    if r == nil {
        return
    }
    fmt.Println("烤羊肉串")
}
func (r *Barbecuer) BakeChickenWing() {
    if r == nil {
        return
    }
    fmt.Println("烤雞翅")
}