golang單例模式的優雅實現

通過sync.Once執行個體來保證一個Once執行個體的Do只會執行一次，無論Do裡的func有多個或者一個，利用這個特性來實現設計模式裡的單例模式，golang裡沒有類這個東西，所以拿結構體來測試:

type singleton struct{}

var ins *singleton

var once sync.Once 

func GetIns() *singleton {

  once.Do(func(){

  ins = &singleton{}

  //ins = new(singleton)

})

return ins

}

sync.Once doc:

type Once

Once is an object that will perform exactly one action.

type Once struct {

    // contains filtered or unexported fields

}

func (*Once) Do

func (o *Once) Do(f func())

Do calls the function f if and only if Do is being called for the first time for this instance of Once. In other words, given

var once Once

if once.Do(f) is called multiple times, only the first call will invoke f, even if f has a different value in each invocation. A new instance of Once is required for each function to execute.