Why does Go handle closures differently in goroutines?

Question

Consider the following Go code (also on the Go Playground):

package main

import "fmt"
import "time"

func main() {
    for _, s := range []string{"foo", "bar"} {
        x := s
        func() {
            fmt.Printf("s: %s
", s)
            fmt.Printf("x: %s
", x)
        }()
    }
    fmt.Println()
    for _, s := range []string{"foo", "bar"} {
        x := s
        go func() {
            fmt.Printf("s: %s
", s)
            fmt.Printf("x: %s
", x)
        }()
    }
    time.Sleep(time.Second)
}

This code produces the following output:

s: foo
x: foo
s: bar
x: bar

s: bar
x: foo
s: bar
x: bar

Assuming this isn't some odd compiler bug, I'm curious why a) the value of s is interpreted differently in the goroutine version then in the regular func call and b) and why assigning it to a local variable inside the loop works in both cases.

Answer 1

Waitting for answers