Question

我正在尝试在golang中定义一个回调：

package main

func main() {
    x, y := "old x ", "old y"
    callback         := func() { print("callback: "        , x        , y       , "\n") }
    callback_bound   := func() { print("callback_bound: "  , x        , y       , "\n") }
    callback_hacked  := func() { print("callback_hacked: " , "old x " , "old y" , "\n") } 

    x, y = "new x ", "new y"

    callback()
    callback_bound()
    callback_hacked()
}

输出结果为：

callback: new x new y
callback_bound: new x new y
callback_hacked: old x old y

基本情况有效，但它使变量保持未绑定状态，即使用呼叫时的值。毫无疑问，这在某些情况下很有用，但是如何声明callback_bound以便使用声明时的值并且输出变为：

callback: new x new y
callback_bound: old x old y
callback_hacked: old x old y

Answer 1

例如，

package main

func callbackXY(x, y string) func() {
    return func() { print("callbackXY: ", x, y, "\n") }
}

func main() {
    x, y := "old x ", "old y"
    callback := callbackXY(x, y)
    x, y = "new x ", "new y"
    callback()
}

输出：

callbackXY: old x old y

或者

package main

func main() {
    x, y := "old x ", "old y"
    callback := func() {}
    {
        x, y := x, y
        callback = func() { print("callbackXY: ", x, y, "\n") }
    }
    x, y = "new x ", "new y"
    callback()
}

输出：

callbackXY: old x old y

Answer 2

bound := func(xx,yy int) { return func(){fmt.Println(xx,yy)} }(x,y)

未测试。

请在http://golang.org/doc/effective_go.html

看一下（或两个）

golang：在回调声明中评估变量

2 个答案: