Avoiding global state

bad.go

package main

import "fmt"

var Enabled bool

func LogEvent(msg string) {
	if Enabled {
		fmt.Println(msg)
	}
}

func doThing() {
	LogEvent("doing a thing")
}

func main() {
	Enabled = true
	doThing()
}

good.go

package main

import "fmt"

type Logger struct {
	Enabled bool
}

func (l *Logger) LogEvent(msg string) {
	if l.Enabled {
		fmt.Println(msg)
	}
}

func doThing(l *Logger) {
	l.LogEvent("doing a thing")
}

func main() {
	l := Logger{Enabled: true}
	doThing(l)
}