Unmarshal de interface{}

main.go

package main

import (
	"encoding/xml"
	"fmt"
)

type Person struct {
	XMLName   xml.Name    `xml:"person"`
	FirstName string      `xml:"firstname"`
	Parents   interface{} `xml:"parent"`
}

func (p *Person) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	type person struct {
		XMLName   xml.Name `xml:"person"`
		FirstName string   `xml:"firstname"`
		Parents   intf     `xml:"parent"`
	}
	var pp person
	pp.Parents = intf{p.Parents}
	if err := d.DecodeElement(&pp, &start); err != nil {
		return err
	}
	p.FirstName = pp.FirstName
	return nil
}

type intf struct {
	value interface{}
}

func (i intf) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	return d.DecodeElement(i.value, &start)
}

func main() {
	type Parent struct {
		FirstName string `xml:"name"`
		LastName  string `xml:"lastname"`
	}
	var p Person
	p.FirstName = "Steve"
	p.Parents = []Parent{{"Jack", "Doe"}, {"Lynne", "Doe"}}
	data, err := xml.Marshal(p)
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println("Marshalled:", string(data))
	var p2 Person
	p2.Parents = new([]Parent)
	err = xml.Unmarshal(data, &p2)
	if err != nil {
		fmt.Println(err)
	}
	fmt.Printf("Unmarshalled: %s\n", p2)
}