golang flag library

main.go

package "main"

import "somelibrary"
import "flags"

func main() {
  someFlag := somelibrary.Impls.Flag()
  flags.Parse()
  someImpl := somelibrary.GetImpl(someFlag)
  run(someImpl)
}

somelibrarythathasflags.go

package somelibrary

type Flag struct {
	param string
	def   string
	desc  string
}

var Impls = Flag{"some", "real", "Some Type"}

func (this Flag) Flag() *string {
	return flag.String(this.param, this.def, this.desc+" "+implUsage())
}

var impls = map[string]impl{
	"mock": mockImpl,
	"real": realImpl,
}

func implUsage() string {
	ss := make([]string, 0, len(impls))
	for i := range impls {
		ss = append(ss, i)
	}
	return "(" + strings.Join(ss, "|") + ")"
}

func GetImpl(impl string) impl {
	return impls[impl]
}