basic_6.go

package main

import (
	"encoding/xml"
	"fmt"
)

type Cat struct {
	XMLName xml.Name `xml:"cat"`
	Name    string   `xml:"name,omitempty"`
	Breed   string   `xml:"breed,omitempty"`
	Age     int      `xml:"age,omitempty"`
	Toy     Toy      `xml:",omitempty"`
}

type Toy struct {
	XMLName xml.Name `xml:"toy"`
	Type    string   `xml:"type,omitempty"`
	Color   string   `xml:"color,omitempty"`
}

func main() {
	cat := Cat{
		Name:  "Olive",
		Breed: "Oriental Shorthair",
		Age:   1,
	}

	bytes, err := xml.MarshalIndent(cat, "", "  ")
	if err != nil {
		panic(err)
	}
	fmt.Println(string(bytes))
}

<cat>
  <name>Olive</name>
  <breed>Oriental Shorthair</breed>
  <age>1</age>
  <toy></toy>
</cat>