options.go

package main

import (
	"fmt"
	"reflect"
)

func main() {
	printUser("poying", 21)
	printUser("poying 2.0")
	printUser("poying 3.0", nil)
}

func printUser(name string, options ...interface{}) {
	age, _ := getOptVal(options, 0, 1).(int)
	fmt.Printf("name: %s\nage: %d\n\n", name, age)
}

func getOptVal(options interface{}, index int, defVal interface{}) interface{} {
	ret := defVal
	s := reflect.ValueOf(options)

	if s.Len() > index {
		ret = s.Index(index).Interface()
	}

	if ret == nil {
		ret = defVal
	}

	return ret
}

http://play.golang.org/p/8IiNcjem9u