Go的panic和recover与错误处理

panic

停止当前函数执行
一直向上返回，执行每一层的defer
如果没有遇见recover，程序退出

func writeFile(filename string) {
	file, err := os.OpenFile(filename,
		os.O_EXCL|os.O_CREATE|os.O_WRONLY, 0666)

	if err != nil {
		if pathError, ok := err.(*os.PathError); !ok {
			panic(err)
		} else {
			fmt.Printf("%s, %s, %s\n",
				pathError.Op,
				pathError.Path,
				pathError.Err)
		}
		return
	}
	defer file.Close()

	writer := bufio.NewWriter(file)
	defer writer.Flush()

	for i := 0; i < 20; i++ {
		fmt.Fprintln(writer, i)
	}
}

recover

仅在defer调用中使用
可以获取panic的值，如果无法处理可以重新panic

func tryRecover() {
	defer func() {
		r := recover()
		if r == nil {
			fmt.Println("Nothing to recover. " +
				"Please try uncomment errors " +
				"below.")
			return
		}
		if err, ok := r.(error); ok {
			fmt.Println("Error occurred:", err)
		} else {
			panic(fmt.Sprintf(
				"I don't know what to do: %v", r))
		}
	}()

	// Uncomment each block to see different panic
	// scenarios.
	// Normal error
	//panic(errors.New("this is an error")) //recover这里是一个错误

	// Division by zero
	//b := 0
	//a := 5 / b
	//fmt.Println(a)

	// Causes re-panic
	//panic(123) //recover这里不知道是啥
}