panic defer recover

defer

1. LIFO, 后进先出队列
2. 在return语句之后，在返回上层函数之前执行
3. 参数预编译，涉及到的参数，在定义defer的地方已经语句赋值了

func c() (i int) {
	defer func() { i++ }()
	return 1
}

func main() {
	fmt.Println(c())
}

return 1将1赋值给i，defer执行，对i进行加1，最终返回值i为2

panic

1. panic类似c语言里的throw，不再执行后面的语句
2. 返回上一层函数之前，依然会执行之前的defer语句
3. 直到遇到recover函数，处理异常，否则程序core

func main() {
	f()
	fmt.Println("Returned normally from f.")
}

func f() {
	defer func() {
		if r := recover(); r != nil {
			fmt.Println("Recovered in f", r)
		}
	}()
	fmt.Println("Calling g.")
	g(0)
	fmt.Println("Returned normally from g.")
}

func g(i int) {
	if i > 3 {
		fmt.Println("Panicking!")
		panic(fmt.Sprintf("%v", i))
	}
	defer fmt.Println("Defer in g", i)
	fmt.Println("Printing in g", i)
	g(i + 1)
}


Calling g.
Printing in g 0
Printing in g 1
Printing in g 2
Printing in g 3
Panicking!
Defer in g 3
Defer in g 2
Defer in g 1
Defer in g 0
Recovered in f 4
Returned normally from f.