http://play.golang.org/p/vtcFCyoLQJ

reflection.go

package main

import (
	"fmt"
	"reflect"
)

type Result interface {
	Value() string
}

type SpecialResult struct {
	value string
}

func (r *SpecialResult) Value() string {
	return r.value
}

func (r *SpecialResult) Special() string {
	return "look I am special!!"
}

func main() {
	sr := &SpecialResult{
		value: "1234",
	}

	doSomething(sr)
}

func doSomething(r Result) {
	switch reflect.TypeOf(r).String() {
	case "*main.SpecialResult":
		fmt.Printf("%s, %s\n", r.Value(), r.(*SpecialResult).Special())
		break
	default:
		fmt.Printf("%s\n", r.Value())
	}
}