defer2.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This file contains the code snippets included in "Defer, Panic, and Recover."

package main

import "fmt"
import "io" // OMIT
import "os" // OMIT

func main() {
	f()
	fmt.Println("Returned normally from f.")
}

func f() {
	defer func() {
		if r := recover(); r != nil {
			fmt.Println("Recovered in f", r)
		}
	}()
	fmt.Println("Calling g.")
	g(0)
	fmt.Println("Returned normally from g.")
}

func g(i int) {
	if i > 3 {
		fmt.Println("Panicking!")
		panic(fmt.Sprintf("%v", i))
	}
	defer fmt.Println("Defer in g", i)
	fmt.Println("Printing in g", i)
	g(i + 1)
}

// STOP OMIT

// Revised version.
func CopyFile(dstName, srcName string) (written int64, err error) {
	src, err := os.Open(srcName)
	if err != nil {
		return
	}
	defer src.Close()

	dst, err := os.Create(dstName)
	if err != nil {
		return
	}
	defer dst.Close()

	return io.Copy(dst, src)
}

// STOP OMIT