Wie entmarshaliere ich dynamische JSON-Felder in Go basierend auf einem Typschlüssel?

type BigStruct struct {
    SomeData     string    `json:"some_data"`
    DynamicField Something `json:"dynamic_field"`
    OtherData    string    `json:"other_data"`
}

type Something interface {
    GetType() string
}

type BaseDynamicType struct {
    Type string `json:"type"`
}

type DynamicTypeA struct {
    BaseDynamicType
    Name string `json:"name"`
}

type DynamicTypeB struct {
    BaseDynamicType
    Address string `json:"address"`
}

func (d *BaseDynamicType) GetType() string {
    return d.Type
}

func (b *BigStruct) UnmarshalJSON(data []byte) error {
    var tmp struct {
        SomeData     string          `json:"some_data"`
        DynamicField json.RawMessage `json:"dynamic_field"`
        OtherData    string          `json:"other_data"`
    }

    if err := json.Unmarshal(data, &tmp); err != nil {
        return err
    }
    b.Unmarshal(tmp.DynamicField)

    return nil
}

func (b *BigStruct) Unmarshal(data json.RawMessage) error {
    switch UnmarshalledType(data) {
    case "A":
        var a DynamicTypeA
        if err := json.Unmarshal(data, &a); err != nil {
            return err
        }

        b.DynamicField = &a
    case "B":
        var b DynamicTypeB
        if err := json.Unmarshal(data, &b); err != nil {
            return err
        }

        b.DynamicField = &b
    }

    return nil
}

func UnmarshalledType(b json.RawMessage) string {
    var typ struct {
        Type string `json:"type"`
    }

    if err := json.Unmarshal(b, &typ); err != nil {
        log.Fatalf("Error extracting type from RawMessage: %v", err)
    }

    return typ.Type
}