golangでデバッグ出力

debug.go

package main

import (
	"flag"
	"log"
	"os"
	"runtime"
)

var debug debugT = false

type debugT bool

func (d debugT) Printf(format string, args ...interface{}) {
	if d {
		pc, file, line, _ := runtime.Caller(1)
		args = append([]interface{}{pc, file, line}, args...)
		log.Printf("%d %s %d: " + format, args...)
	}
}

func init() {
	if os.Getenv("GODEBUG") != "" {
		debug = true
	} else {
		usage := "debug"
		ptr := (*bool)(&debug)
		flag.BoolVar(ptr, "debug", false, usage)
		flag.BoolVar(ptr, "d", false, usage + " (shorthand)")
	}
}

func main() {
	flag.Parse()

	debug.Printf("this is %s message", "DEBUG")
}

flagパッケージも組み合わせてみた