defer.go

//
// gobyexample.com
// defer.go
//
package main

import (
	"fmt"
	"os"
)

func main() {

	// Suppose we wanted to create a file, write to it,
	// and then close when we’re done.
	//
	// Here’s how we could do that with defer.
	f := createFile("/tmp/defer.txt")
	defer closeFile(f)
	writeFile(f)
}

// Immediately after getting a file object with createFile,
// we defer the closing of that file with closeFile.
//
// This will be executed at the end of the enclosing function (main),
//  after writeFile has finished.

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")

}

// It’s important to check for errors when closing a file,
// even in a deferred function.
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)
	}
}