Default value in a struct

/*
    set default values for a struct being Unmarshaled from json
*/
package main

import (
    "encoding/json"
    "fmt"
)

type Out struct {
    A string `json:"a"`
    B string `json:"b"`
    C string `json:"c"`
    D int    `json:"d"`
}

func main() {
    in := []byte(`{"a":"1"}`)
    out := Out{
        A: "defaultA",
        B: "defaultC",
        C: "defaultD",
        D: 99,
    }
    json.Unmarshal(in, &out)
    fmt.Printf("%+v\n ", out)
}