"Decorator Pattern in Go" learned from GopherCon 2015.

decorator-sample.go

package main

import (
	"fmt"
	"time"
)

type Worker interface {
	Do(string) bool
}

type WorkerFunc func(s string) bool

func (w WorkerFunc) Do(s string) bool {
	return w(s)
}

type WorkerDecorator func(Worker) Worker

func LoggingDecorator(header string) WorkerDecorator {
	return func(w Worker) Worker {
		return WorkerFunc(func(s string) bool {
			fmt.Printf("%s: start.\n", header)
			defer fmt.Printf("%s: End.\n", header)
			return w.Do(s)
		})
	}
}

func AuthorizationDecorator(token string) WorkerDecorator {
	return func(w Worker) Worker {
		return WorkerFunc(func(s string) bool {
			fmt.Printf("Authorizing with token: %s\n", token)
			return w.Do(s)
		})
	}
}

func RetryDecorator(attempts int, interval time.Duration) WorkerDecorator {
	return func(w Worker) Worker {
		return WorkerFunc(func(s string) (res bool) {
			for i := 1; i <= attempts; i++ {
				fmt.Printf("Attempt: %d.\n", i)
				if res = w.Do(s); res == true {
					break
				}
				time.Sleep(interval)
			}
			return res
		})
	}
}

func WorkerDecorate(w Worker, ds ...WorkerDecorator) Worker {
	decorated := w
	for _, decorator := range ds {
		decorated = decorator(decorated)
	}
	return decorated
}

type PrintWorker struct{}

func (*PrintWorker) Do(s string) bool {
	fmt.Printf("PrintWorker: Doing %s.\n", s)
	return true
}

func main() {
	decoratedWorker := WorkerDecorate(&PrintWorker{},
		LoggingDecorator("Decorator-sample logging"),
		AuthorizationDecorator("jhfaHkjfhwGquadN"),
		RetryDecorator(3, 2*time.Second))
	decoratedWorker.Do("some serious works")
}