除非复制变量，否则go例程中的闭包的作用域不正确

Question

I am seeing incorrect values in the functions run as goroutines. They don't seem to be capturing the values from the scope in which they were invoked unless copied into new variables.

http://play.golang.org/p/YZYi-IVuYm

vs.

http://play.golang.org/p/z88G99XSi6

Answer 1

You either need to re-assign the variable in the local context so that the closure can capture the values:

http://play.golang.org/p/-NO4S4qCZf

package main

import "fmt"
import "time"

func main() {
    l := []int{1, 2, 3}
    for idx, item := range l {
        theIdx, theItem := idx, item
        go func() {
            fmt.Println(theIdx, theItem)
        }()
    }
    time.Sleep(time.Second)
}

or you pass the values to the goroutine and add parameters to the function

http://play.golang.org/p/5gNToDWSQR

package main

import "fmt"
import "time"

func main() {
    l := []int{1, 2, 3}
    for idx, item := range l {
        go func(idx, item int) {
            fmt.Println(idx, item)
        }(idx, item)
    }
    time.Sleep(time.Second)
}