Command

Muammo: amalni (kim, nimani, qanday bajaradi) bitta obyektga o’rab olishingiz kerak - uni navbatga qo’yish, tarixini saqlash yoki bekor qilish (undo) uchun. Amalni oddiy funksiya chaqiruvi qilib qoldirsangiz, uni “ushlab” saqlab bo’lmaydi.

G’oya: har bir amalni Execute (va kerak bo’lsa Undo) metodli obyektga aylantirasiz. “Invoker” ularni bajaradi va tarixga yozadi - shu bilan undo, qayta bajarish, navbat oson bo’ladi.

command.go


package main
 
import "fmt"
 
// Command - bajariladigan va bekor qilinadigan amal.
type Command interface {
	Execute()
	Undo()
}
 
type Document struct {
	text string
}
 
// AppendCommand hujjatga matn qo'shadi.
type AppendCommand struct {
	doc   *Document
	added string
}
 
func (c *AppendCommand) Execute() { c.doc.text += c.added }
func (c *AppendCommand) Undo()    { c.doc.text = c.doc.text[:len(c.doc.text)-len(c.added)] }
 
// Invoker buyruqlarni bajaradi va tarixni saqlaydi.
type Invoker struct {
	history []Command
}
 
func (in *Invoker) Run(c Command) {
	c.Execute()
	in.history = append(in.history, c)
}
 
func (in *Invoker) UndoLast() {
	if len(in.history) == 0 {
		return
	}
	last := in.history[len(in.history)-1]
	in.history = in.history[:len(in.history)-1]
	last.Undo()
}
 
func main() {
	doc := &Document{}
	inv := &Invoker{}
 
	inv.Run(&AppendCommand{doc: doc, added: "Salom"})
	inv.Run(&AppendCommand{doc: doc, added: ", dunyo"})
	inv.Run(&AppendCommand{doc: doc, added: "!!!"})
	fmt.Printf("matn: %q\n", doc.text)
 
	inv.UndoLast()
	fmt.Printf("undo keyin: %q\n", doc.text)
}


$ go run command.go
matn: "Salom, dunyo!!!"
undo keyin: "Salom, dunyo"

Har bir amal obyekt bo’lgani uchun Invoker ularni tarixda saqlab, oxirgisini bekor qila oldi.

Qachon: undo/redo, vazifa navbati, tranzaksiya jurnali kerak bo’lganda. Go note: undo shart bo’lmasa, ko’pincha Command interfeysi o’rniga oddiy func() yetadi.

Manba / batafsil: refactoring.guru/design-patterns/command