Handling errors in short programs

Propagating errors up to the callers is tedious. You end up with many lines looking like:

r, err := os.Open("my file")
if err != nil {
    return err
}

This kind of error handling diligence is crucial for writing robust software.

Sometimes you write shorter cmd-line programs where such discipline is not warranted.

You can simplify error handling with a helper functions PanicIfErr(err error, args ...interface{}):

r, err := os.Open("my file")
PanicIfErr(err)

Implementation of such helper:

// FmtArgs formats args as a string. First argument should be format string
// and the rest are arguments to the format
func FmtArgs(args ...interface{}) string {
	if len(args) == 0 {
		return ""
	}
	format := args[0].(string)
	if len(args) == 1 {
		return format
	}
	return fmt.Sprintf(format, args[1:]...)
}

func panicWithMsg(defaultMsg string, args ...interface{}) {
	s := FmtArgs(args...)
	if s == "" {
		s = defaultMsg
	}
	fmt.Printf("%s\n", s)
	panic(s)
}

// PanicIf panics if cond is true
func PanicIf(cond bool, args ...interface{}) {
	if !cond {
		return
	}
	panicWithMsg("PanicIf: condition failed", args...)
}

// PanicIfErr panics if err is not nil
func PanicIfErr(err error, args ...interface{}) {
	if err == nil {
		return
	}
	panicWithMsg(err.Error(), args...)
}

func main() {
	PanicIfErr(nil)                              // nothing happens
	PanicIfErr(errors.New("there was an error")) // will panic
}

try online

there was an error
panic: there was an error

goroutine 1 [running]:
main.panicWithMsg(0x4c5081, 0x12, 0x0, 0x0, 0x0)
	/tmp/src099150232/main.go:30 +0x126
main.PanicIfErr(0x4dc8c0, 0xc00005a1e0, 0x0, 0x0, 0x0)
	/tmp/src099150232/main.go:46 +0x6c
main.main()
	/tmp/src099150232/main.go:51 +0x84
exit status 2

Found a mistake? Have a question or improvement idea? Let me know.

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