Decorator

Muammo: mavjud obyektga yangi xatti-harakat (log, vaqt o’lchash, kesh) qo’shmoqchisiz, lekin uning kodini o’zgartirmasdan va har bir kombinatsiya uchun alohida tur yaratmasdan.

G’oya: obyektni bir xil interfeysli boshqa obyekt bilan o’raysiz. O’ragich (decorator) o’z ishini bajaradi va ichkaridagiga murojaat qiladi. Qatlamlarni istagancha ustma-ust qo’yish mumkin - bu HTTP middleware’ning asosidir.

decorator.go


package main
 
import (
	"fmt"
	"strings"
)
 
type Handler interface {
	Handle(request string) string
}
 
// Yadro handler.
type EchoHandler struct{}
 
func (EchoHandler) Handle(request string) string {
	return "javob: " + strings.ToUpper(request)
}
 
// LoggingDecorator boshqa Handler ni o'rab, log qo'shadi.
type LoggingDecorator struct {
	next Handler
}
 
func (d LoggingDecorator) Handle(request string) string {
	fmt.Printf("LOG: so'rov keldi -> %q\n", request)
	resp := d.next.Handle(request)
	fmt.Printf("LOG: javob qaytdi -> %q\n", resp)
	return resp
}
 
func main() {
	var h Handler = EchoHandler{}
	h = LoggingDecorator{next: h} // yadroni o'raymiz
 
	fmt.Println(h.Handle("salom"))
}


$ go run decorator.go
LOG: so'rov keldi -> "salom"
LOG: javob qaytdi -> "javob: SALOM"
javob: SALOM

EchoHandler o’zgarmadi; log qatlamini uning ustidan kiydik. Yana bir decorator qo’shsangiz, h = TimingDecorator{next: h} deb davom etasiz.

Qachon: funksionallikni qatlam-qatlam qo’shish kerak bo’lganda. Go note: bu pattern Go da middleware ko’rinishida gullab-yashnaydi - Middleware sahifasiga qarang.

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