json-test2.go

package main

import (
  "encoding/json"
	"log"
)

func main() {
	// JSON wrapping test
	var data struct {
		X  float64          `json:"x,string"`
		Id *json.RawMessage `json:"id"`
		Y  float32          `json:"y"`
	}
	const msg = `{"x":"0.1","id":["\u0056",null],"y":0.2}`
	err := json.Unmarshal([]byte(msg), &data)
	if err != nil {
		panic(err.Error())
	}
	log.Println(data)

	replace := []byte(`{"msg":"this is replaced json"}`)
	if err = data.Id.UnmarshalJSON(replace); err != nil {
		panic(err.Error())
	}
	data.X = data.X * 2

	log.Println(data)

	b, err := json.Marshal(&data)
	if err != nil {
		panic(err.Error())
	}

	log.Println(string(b))
}