gistfile1.go

package main

import "sync"

type SingleCounter struct {
	count int
}

var counter *SingleCounter

type Manager struct {
	counter *SingleCounter
	once    sync.Once
}

func NewManager() *Manager {
	manager := new(Manager)
	manager.once.Do(func() {
		counter = new(SingleCounter)
	})
	manager.counter = counter
	return manager
}

gistfile2.go

package main

import "sync"

type SingleCounter struct {
	count int
}

var counter *SingleCounter
var counterInit sync.Once

func getCounter() *SingleCounter {
	counterInit.Do(func() {
		counter = new(SingleCounter)
	})
	return counter
}

type Manager struct {
	counter *SingleCounter
}

func NewManager() *Manager {
	return &Manager{counter: getCounter()}
}

gistfile3.go

package main

import "sync"

type SingleCounter struct {
	count int
}

var getCounter = func() func() *SingleCounter {
	var counter *SingleCounter
	var counterInit sync.Once

	return func() *SingleCounter {
		counterInit.Do(func() {
			counter = new(SingleCounter)
		})
		return counter
	}
}()

type Manager struct {
	counter *SingleCounter
}

func NewManager() *Manager {
	return &Manager{counter: getCounter()}
}