英文:
golang: evaluate variable in callback declaration
问题
我正在尝试在Go语言中定义一个回调函数：
package main
func main() {
x, y := "old x ", "old y"
callback := func() { print("callback: ", x, y, "\n") }
callback_bound := func(a, b string) func() {
return func() { print("callback_bound: ", a, b, "\n") }
}(x, y)
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: old x old y
callback_hacked: old x old y
基本情况下是可以工作的，但它会使变量未绑定，即在调用时使用的是值。毫无疑问，这在某些情况下是有用的，但我该如何声明callback_bound，以便在声明时使用变量的值，使输出变为：
callback: new x new y
callback_bound: old x old y
callback_hacked: old x old y
英文:
I am trying to define a callback in golang:
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()
}
The output is:
callback: new x new y
callback_bound: new x new y
callback_hacked: old x old y
The basic case works, but it leaves the variables unbound, i.e. the values at call-time are used. No doubt, this is useful in some cases, but how do I declare callback_bound so that the values at declaration-time are used and the output becomes:
callback: new x new y
callback_bound: old x old y
callback_hacked: old x old y
答案1
得分: 2
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
英文:
For example,
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()
}
Output:
callbackXY: old x old y
Or
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()
}
Output:
callbackXY: old x old y
答案2
得分: -1
bound := func(xx, yy int) { return func() { fmt.Println(xx, yy) } }(x, y)
未经测试。
请查看（或两次）http://golang.org/doc/effective_go.html
英文:
bound := func(xx,yy int) { return func(){fmt.Println(xx,yy)} }(x,y)
Untested.
Please have a look (or two) at http://golang.org/doc/effective_go.html
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