go - Adding Arbitrary fields to json output of an unknown struct

Question

In this stackoverflow post it's explained how to add arbitrary fields to a golang struct by using it as an anonymous. This works fine if you are working with known struct types, but I'm wondering how to do the same thing when dealing with an unknown struct or interface.

I wrote the following example to demonstrate:

package main

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

type example interface{}
type Data struct {
    Name string
}

func printInterface(val interface{})    {
    example1 := struct {
        example
        Extra string
    }{
        example: val,
        Extra: "text",
    }
    json.NewEncoder(os.Stdout).Encode(example1)
}

func printStructPointer(val *Data)  {
    example2 := struct {
        *Data
        Extra string
    }{
        Data: val,
        Extra: "text",
    }
    json.NewEncoder(os.Stdout).Encode(example2)
}


func main() {
    d := Data{Name:"name"}
    fmt.Println("Example 1:")
    printInterface(&d)
    fmt.Println("Example 2:")
    printStructPointer(&d)
}

This prints the following:

Example 1:
{"example":{"Name":"name"},"Extra":"text"}
Example 2:
{"Name":"name","Extra":"text"}

I'm so assuming that I was working within printInterface how do get the JSON output to look like the JSON output of printStructPointer?

Answer 1

Waitting for answers