package main

import (
    "fmt"
    "encoding/json"
)

type Base struct {
    A int `json:"a"`
}

type Container struct {
    Base
    B int `json:"b"`
}

func main() {
    data := []byte("{\"a\":10,\"b\":20}")
    var c Container

    if err := json.Unmarshal(data, &c); err != nil {
        panic(err)
    }

    fmt.Println(c)
}