Singleton in go

Question

How does one implement the Singleton design pattern in the go programming language?

Answer 1

You can do initialization using the once package:

This will ensure that your init methods only get called once.

Answer 2

Just put your variables and functions at the package level.

Also see similar question: How to make a singleton in Python

Answer 3

Easy peasy as you can see in the following code:

package main

import (
    "fmt"
    "sync"
)

type singleton struct {
    count int
    sync.RWMutex
}

var instance singleton 

func GetInstance() *singleton {
    return &instance 
}

func (s *singleton) AddOne() {
    s.Lock()
    defer s.Unlock()
    s.count++
}

func (s *singleton) GetCount() int {
    s.RLock()
    defer s.RUnlock()
    return s.count
}

func main() {
    obj1 := GetInstance()
    obj1.AddOne()
    fmt.Println(obj1.GetCount())
    obj2 := GetInstance()
    obj2.AddOne()
    fmt.Println(obj2.GetCount())    
    obj3 := GetInstance()
    obj3.AddOne()
    fmt.Println(obj3.GetCount())
}

Expected result would be:

1 2 3

Because you're accessing to the same resource. That's the reason I've added mutex in order to be concurrent proven accessing count attribute from multiple processes. :-)

Source:

https://play.golang.org/p/2XnLztX8Gs5