How to marshal struct when some members are protected/inner/hidden

How do ensure the fields in this LookupCode struct are included when marshalling?

package main

import (
	"encoding/json"
	"fmt"
)

type LookupCode struct {
	code string `json:"code"`
	name string `json:"name"`
}

func (l *LookupCode) GetCode() string {
	return l.code
}

func main() {
	c := &LookupCode{
		code: "A",
		name: "Apple",
	}

	b, _ := json.MarshalIndent(c, "", "\t")

	fmt.Println(string(b))
}

http://play.golang.org/p/my52DAn0-Z

You can by implementing the json.Marshaller interface:

Full Example: http://play.golang.org/p/8mIcPwX92P

// Implement json.Unmarshaller
func (l *LookupCode) UnmarshalJSON(b []byte) error {
	var tmp struct {
		Code string `json:"code"`
		Name string `json:"name"`
	}
	err := json.Unmarshal(b, &tmp)
	if err != nil {
		return err
	}
	l.code = tmp.Code
	l.name = tmp.Name
	return nil 
}

func (l *LookupCode) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		Code string `json:"code"`
		Name string `json:"name"`
	}{
		Code: l.code,
		Name: l.name,
	})
}

encode/json cannot marshal unexported fields. Change your code to:

type LookupCode struct {
    Code string `json:"code"`
    Name string `json:"name"`
}

and do the same wherever you use code or name.

Playground: http://play.golang.org/p/rak0nVCNGI

Edit

The limitation is due to the reflection used when marshalling the struct. If you need to keep your values unexported, you must implement the json.Marshaller interface and do the encoding manually.

if the struct has only string-type fields,you can try this hack way.

package main

import (
    "fmt"
    "reflect"

    "github.com/bitly/go-simplejson"
)

type A struct {
    name string `json:"name"`
    code string `json:"code"`
}

func marshal(a A) ([]byte, error) {
    j := simplejson.New()
    va := reflect.ValueOf(&a)
    vt := va.Elem()
    types := reflect.TypeOf(a)
    for i := 0; i < vt.NumField(); i++ {
        j.Set(types.Field(i).Tag.Get("json"), fmt.Sprintf("%v", reflect.Indirect(va).Field(i)))
    }
    return j.MarshalJSON()
}

func main() {
    a := A{name: "jessonchan", code: "abc"}
    b, _ := marshal(a)
    fmt.Println(string(b))
}