package main

import (
    "fmt"
    "encoding/json"
    ms "github.com/mitchellh/mapstructure"
)

type Value struct {
    Key      string
    OtherKey interface{}
}

type OtherKeyValue struct {
    OtherOtherKey string
}

func main() {
    // Construct value to marshal
    val := Value{Key: "yo", OtherKey: OtherKeyValue{OtherOtherKey: "yo2"}}
    fmt.Printf("Struct: %v\n", val)

    // Marshal
    b, err := json.Marshal(val)
    if err != nil {
        fmt.Printf("Error marshalling: %s\n", err)
        return
    }
    fmt.Printf("Marshalled: %s\n", string(b))

    // Unmarshal
    var toFill Value
    if err := json.Unmarshal(b, &toFill); err != nil {
        fmt.Printf("Error unmarshalling: %s\n", err)
        return
    }
    fmt.Printf("Unmarshalled: %v\n", toFill)

    // Cast
    var otherKeyValue OtherKeyValue
    ms.Decode(toFill.OtherKey, &otherKeyValue)
    fmt.Printf("Other key value: %v\n", otherKeyValue)
}