1 package main
2
3 import (
4 "fmt"
5 "time"
6 )
7
8 func sum(a ...int) int {
9 defer trace("sum")() // note:不要忘记defer语句后的圆括号，否则本该在进入时执行的操作会在退出时执行，而本该在退出时执行的，永远不会执行
10 total := 0
11 for _, val := range a {
12 total += val
13 }
14 return total
15 }
16
17 func trace(msg string) func() {
18 start := time.Now()
19 fmt.Printf("enter %s\n", msg)
20 return func() {
21 fmt.Printf("exit %s (%s)\n", msg, time.Since(start))
22 }
23 }
24
25 func main() {
26 count := sum(3, 5, 9)
27 fmt.Printf("%d\n", count)
28 }
执行结果：
1 enter sum
2 exit sum (194.764µs)
3 17
利用defer修改函数的返回值：
1 package main
2
3 import (
4 "fmt"
5 "time"
6 )
7
8 func sum(a, b int) (result int) {
9 //defer trace("sum")() // note:不要忘记defer语句后的圆括号，否则本该在进入时执行的操作会在退出时执行，而本该在退出时执行的，永远不会执行
10 defer func() { result += a }() //被延时执行的匿名函数甚至可以修改函数返回给调用者的返回值
11 result = 0
12 result += a
13 result += b
14 return result
15 }
16
17 func trace(msg string) func() {
18 start := time.Now()
19 fmt.Printf("enter %s\n", msg)
20 return func() {
21 fmt.Printf("exit %s (%s)\n", msg, time.Since(start))
22 }
23 }
24
25 func main() {
26 count := sum(3, 8)
27 fmt.Printf("%d\n", count)
28 }
执行结果：
1 [root@docker pro]# go run arg.go
2 [root@docker pro]# go run arg.go
3 14
