leveledLogger.go

package main

import "fmt"

const (
	debugLevel = iota
	infoLevel
	warnLevel
	errorLevel
	fatalLevel
	logLevelCount
)

type logFn func(s string, a ...interface{})

func initLogFuncs() []logFn {
	logFuncs := make([]logFn, logLevelCount)
	for level := 0; level <= fatalLevel; level++ {
		if logLevel <= level {
			logFuncs[level] = func(s string, a ...interface{}) {
				fmt.Printf(s, a...)
			}
			continue
		}

		logFuncs[level] = func(string, ...interface{}) {}
	}
	return logFuncs
}

var logFuncs = initLogFuncs()

var (
	logDebug = logFuncs[debugLevel]
	logInfo  = logFuncs[infoLevel]
	logWarn  = logFuncs[warnLevel]
	logError = logFuncs[errorLevel]
	logFatal = logFuncs[fatalLevel]
)

const logLevel = infoLevel

func main() {
	logDebug("debug message\n")
	logInfo("info message\n")
	logWarn("warning message\n")
	logError("error message\n")
	logFatal("fatal message\n")
}