Go: a list of structure field names

package main

import (
 "fmt"
 "reflect"
)

type User struct {
 Name     string
 Age      int
 Password string
}

func GetFieldNames(s interface{}) []string {
 t := reflect.TypeOf(s)
 if t.Kind() == reflect.Ptr {
  t = t.Elem()
 }
 if kind := t.Kind(); kind != reflect.Struct {
  fmt.Printf("not a struct kind: %s", kind)
  return nil
 }
 var ret []string
 for i := 0; i < t.NumField(); i++ {
  field := t.Field(i)
  ret = append(ret, field.Name)
 }
 return ret
}

func main() {
 u := User{}
 fmt.Println(GetFieldNames(u))
 fmt.Println(GetFieldNames(&u))
}

At Go Playground: http://play.golang.org/p/6LDoCIKFeH
The function returns a slice of strings. Each is a name of a field. If a pointer is an argument the underlying type's field names are returned. The function ended up in: github.com/orian/utils/reflect. A documentation is browsable at: https://gowalker.org/github.com/orian/utils/reflect.
A short explanation:

• First get a reflect.Type of a given argument s
• If s' kind is a pointer, get a descriptor of underlying type.
• If underlying type is not a struct, return error..
• Iterate over fields, add field names and return the result slice.