Singleton

Оригинальная статья: https://medium.com/german-gorelkin/go-singleton-f408a6c11a55

import "sync"

var addCh chan bool = make(chan bool)
var getCountCh chan chan int = make(chan chan int)
var quitCh chan bool = make(chan bool)

type Singleton interface {
   AddOne()
   GetCount() int
   Stop()
}

type singleton struct {
   count int
}

var instance *singleton
var once sync.Once

func GetInstance() Singleton {
   once.Do(func() {
      instance = new(singleton)

      go func() {
         for {
            select {
            case <-addCh:
               instance.count++
            case ch := <-getCountCh:
               ch <- instance.count
            case <-quitCh:
               return
            }
         }
      }()
   })

   return instance
}

func (s *singleton) AddOne() {
   addCh <- true
}

func (s *singleton) GetCount() int {
   resCh := make(chan int)
   defer close(resCh)
   getCountCh <- resCh
   return <-resCh
}

func (s *singleton) Stop() {
   quitCh <- true
   close(addCh)
   close(getCountCh)
   close(quitCh)
   instance = nil
}