dynamic json in lists

main.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
)

const inputSound = `
{
	"type": "sound",
	"msg": [{
    "this": "that",
    "sound": "stuff"
  }]
}`

const inputSound = `
{
	"type": "visual",
	"msg": [{
    "this": "that",
    "visual": "stuff"
  }]
}`

type Envelope struct {
	Type string
	Msg  interface{}
}

type Sound struct {
	This  string
	Sound string
}

type Visual struct {
	This   string
	Visual string
}

func main() {
	var msg json.RawMessage

	env := Envelope{
		Msg: &msg,
	}

	if err := json.Unmarshal([]byte(inputSound), &env); err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%+v", env)

	switch env.Type {
	case "sound":
		var sound Sound
		if err := json.Unmarshal(msg, &sound); err != nil {
			log.Fatal(err)
		}
		env.Msg = sound
	}

	for _, item := range env.Msg {
		fmt.Println(item.This)
	}
}