defer的执行程序

多个defer是一个栈的构造，是先进后出，上面这个代码的输入程序是CBA。

package mainimport "fmt"func main() {    defer func1()    defer func2()    defer func3()}func func1() {    fmt.Println("A")}func func2() {    fmt.Println("B")}func func3() {    fmt.Println("C")}

defer和return的程序

先执行return，再执行defer。

package mainimport "fmt"func deferFunc() {    fmt.Println("defer func called")}func returnFunc() int {    fmt.Println("return func called")    return 0}func returnAndDefer() int {    defer deferFunc()    return returnFunc()}func main() {    returnAndDefer()}// output:// return func called // defer func called

函数命名返回值遇见defer

package mainimport "fmt"func foo() (t int) {    defer func() {        t = t * 10    }()    return 1}func main() {    fmt.Println(foo())}// output: 10

defer和panic

panic阻断defer

import (    "fmt")func deferFn() {    defer func() { fmt.Println("defer before panic 1") }()    defer func() { fmt.Println("defer before panic 2") }()    panic("exit")    defer func() { fmt.Println("defer after panic") }()}func main() {    deferFn()    fmt.Println("main exit")}/*output:defer before panic 2defer before panic 1panic: exit...*/

defer外面的recover

defer在panic 后仍然无效

package mainimport (    "fmt")func deferFn() {    defer func() {        fmt.Println("defer before panic 1")        if err := recover(); err != nil {            fmt.Println(err)        }    }()    defer func() { fmt.Println("defer before panic 2") }()    panic("panic info")    defer func() { fmt.Println("defer after panic") }()}func main() {    deferFn()    fmt.Println("main exit")}/*output:defer before panic 2defer before panic 1panic infomain exit*/

defer中蕴含panic

panic仅有最初一个能够被revover捕捉

package mainimport (    "fmt")func main() {    defer func() {        if err := recover(); err != nil {            fmt.Println(err)        } else {            fmt.Println("defer call")        }    }()    defer func() {        panic("defer panic")    }()    panic("main panic")}// output: defer panic

defer中函数有参数和蕴含子函数

package mainimport "fmt"func foo(index int, value int) int {    fmt.Println(index)    return index}func main() {    defer foo(1, foo(3, 0))    defer foo(2, foo(4, 0))}// output: 3 4 2 1

测试练习

package mainimport "fmt"func DeferFunc1(i int) (t int) {    t = i    defer func() {        t += 3    }()    return t}func DeferFunc2(i int) int {    t := i    defer func() {        t += 3    }()    return t}func DeferFunc3(i int) (t int) {    defer func() {        t += i    }()    return 2}func DeferFunc4() (t int) {    defer func(i int) {        fmt.Println(i)        fmt.Println(t)    }(t)    t = 1    return 2}func main() {    fmt.Println(DeferFunc1(1))    fmt.Println(DeferFunc2(1))    fmt.Println(DeferFunc3(1))    DeferFunc4()}