golang之defer（统计函数执行时间）

 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 }

1 enter sum
2 exit sum (194.764µs)
3 17

 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 }

1 [root@docker pro]# go run arg.go 
2 [root@docker pro]# go run arg.go 
3 14