go如何优雅的写单例？

package main

import "fmt"

var instance *singleton

func getInstance() *singleton {
    if instance == nil {
        instance = &singleton{}
    }
    return instance
}

type singleton struct{}

func (s *singleton) doSomething() {
    fmt.Println("Doing something...")
}

func main() {
    s1 := getInstance()
    s1.doSomething()

    s2 := getInstance()
    s2.doSomething()

    fmt.Printf("s1 and s2 are the same instance: %v\n", s1 == s2)
}