effect

Used to ensure that the function is called later in the program execution . Usually used for cleaning purposes .

Case study

First implement the method ：

func createFile(p string) *os.File {
    
	fmt.Println("creating")

	f, err := os.Create(p)
	if err != nil {
    
		panic(err)
	}
	return f
}

func writeFile(f *os.File) {
    
	fmt.Println("writing")
	fmt.Fprintln(f, "data")
}

func closeFile(f *os.File) {
    
	fmt.Println("closing")
	err := f.Close()
	if err != nil {
    
		fmt.Fprintf(os.Stderr, "error:%v\n", err)
		os.Exit(1)
	}
}

And then call the method , Realize file creation 、 Data writing 、 File closing function .

f := createFile("/tmp/defer.txt")
defer closeFile(f)
writeFile(f)

The final result is as follows ：

creating
writing
closing