go panic And recover

go Unlike python equally , Yes try-except grammar , The method of exception capture is also not recommended , It's the way to return the exception directly , And it will be more convenient to exit directly than to return layer by layer . therefore go Implemented in the panic- recover Mechanism . It is specially used to throw and recover these exceptions . however stay go It is more recommended to use Wrong type , instead of Use panic and recover. Only when the program cannot continue to run , Should use panic-recover Mechanism .

panic

panic For active throwing of exceptions , Be similar to python Medium raise

panic There are two reasonable use cases .

1. An unrecoverable error occurred , The program cannot continue at this time . One example is web The server was unable to bind the required port . under these circumstances , You should use panic, Because if you can't bind the port , Nothing can be done .

2. A programming error has occurred . Let's say we have a way to receive pointer parameters , And others use it nil It is called as an argument . under these circumstances , We can use panic, Because this is a programming error ： use nil Parameter called a method that can only receive legal pointers .

Example

func main() {
    
	fmt.Println(" I started a ")
	panic(" I made a mistake ")
	fmt.Println(" I'm finished ")
}

recover

recover Used to restore program operation , however recover The correct use of 2 Point needs attention

1. recover Must cooperate defer Use
2. recover Must be in defer The first layer under closures or calling functions uses

Example

func main() {
    
	fmt.Println(" I started a ")
	// recover() //  No error is reported during execution , So it doesn't work 
	defer func() {
         //  Use... Correctly 1
		recover()
	}()
	// defer Test4() //  Use... Correctly 2
	panic(" I made a mistake ")
	// recover() //  After reporting an error, it cannot be implemented here , So it doesn't work 
	fmt.Println(" I'm finished ")
}

func Test4()  {
    
	recover()
}

It should be noted that ,recover It can resume the operation of the program , however This floor The subsequent code of will not be executed . The function or method will be skipped directly , Execute other code

func main() {
    
	f1()
	f2()
	f3()
}

func Test4()  {
    
	recover()
}

func f1()  {
    
	fmt.Println(" I am a f1")
}
func f2()  {
    
	defer Test4()  //  Use... Correctly 2
	panic("f2 Wrong report ")
	fmt.Println(" I am a f2")
}
func f3()  {
    
	fmt.Println(" I am a f3")
}

go Exception handling template in

contrast python Medium try-except-finallly, stay go We can also use recover + defer + if The way of judgment , The code is as follows :

defer func() {
    
	if err := recover(); err != nil {
    
		fmt.Println(err)   //  Type of printing error , python in  except  The code in 
	}
	fmt.Println("python in finally Code for ")
}

Put this code , Just put it above the code that may go wrong , Of course, you can also write the above correct use 2, To use .