identify the type of an object dynamically while reading json data

Quite new to go, sorry if this question sounds obvious.

I would like to use reflection in order to identify the type of an object while reading a json file.

The use case (please see the code below) is the following: I have two structs BoyGift and GirlGift that contain different fields. I have also a Boolean indicator IsBoy that is true if the recipient of the giftis a boy, false otherwise.

The type that encapsulates this behavior is the type Gift:

//Gift type
type Gift struct {
    IsBoy   bool     `json:"isBoy"`
    Payload ??? `json:"payload"`
}

that holds the data. How can I define that type in order the json unmarshal to convert dynamically to the correct type? The "json schema" in this case defines that a Gift should be either a BoyGift or a GirlGift. Is it possible to do this via reflection? How?

package main

import (
    "encoding/json"
    "fmt"
)

//BoyGift type
type BoyGift struct {
    Cars  uint32 `json:"cars"`
    Balls uint32 `json:"balls"`
}

//GirlGift type
type GirlGift struct {
    Dolls uint32 `json:"dolls"`
    Lego  uint32 `json:"lego"`
}

//Gift type
type Gift struct {
    IsBoy   bool     `json:"isBoy"`
    Payload GirlGift `json:"payload"`
}

func main() {

    b := []byte(`{
        "isBoy": true,
        "payload": {
          "cars": 1,
          "balls": 2
        }
      }`)

    var g Gift
    err := json.Unmarshal(b, &g)

    if err != nil {
        fmt.Println(err)
        return
    }

    fmt.Println(g)
}