package main

// defer is used to ensure that a function call is performed later in
// a program's execution, usually for purposes of cleanup.

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.

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

func createFile(p string) *os.File {
	fmt.Println("creating file", p)
	f, err := os.Create(p)
	if err != nil {
		panic(err)
	}
	return f
}

func closeFile(f *os.File) {
	fmt.Println("closing file")
	err := f.Close()

	if err != nil {
		fmt.Fprintf(os.Stderr, "error: %v\n", err)
		os.Exit(1)
	}
}

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