json_structs.go

package main

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

var data = `
{"menu": {
  "id": "file",
  "value": "File",
  "tf": null,
  "popup": {
    "menuitems": [
      {"value": "New", "onclick": "CreateNewDoc()"},
      {"value": "Open", "onclick": "OpenDoc()"},
      {"value": "Close", "onclick": "CloseDoc()"}
    ]
  }
}}`

func main() {
	// a crazy specific struct with a huge number of levels
	// when declared on the fly like this, we call these anonymous structs
	s := struct {
		Menu struct {
			Id    string `json:"id"`
			Value string `json:"value"`
			Popup struct {
				MenuItems []struct {
					Value   string `json:"value"`
					OnClick string `json:"onclick"`
				} `json:"menuitems"`
			} `json:"popup"`
		} `json:"menu"`
	}{} // this last '{}' initializes the struct so it's an instance rather than a type

	// you can turn strings into an array of bites with this trick
	dataAsBytes := []byte(data)

	// always pass the pointer (the address of the thing) to what you're decoding into
	// this is what the '&' is for
	err := json.Unmarshal(dataAsBytes, &s)
	if err != nil {
		log.Fatal(err) // always check your errors
	}
	fmt.Printf(".menu.id: '%s'\n", s.Menu.Id)
	fmt.Printf(".menu.popup.menuitems.[0].value: '%s'\n", s.Menu.Popup.MenuItems[0].Value)
	fmt.Printf(".menu.popup.menuitems.[0].onclick: '%s'\n", s.Menu.Popup.MenuItems[0].OnClick)

	// we can totally just use the fields now
	items := s.Menu.Popup.MenuItems
	fmt.Printf(".menu.popup.menuitems: %s\n", items)
}