Alternative union representation

// union foo {
//     int i;
//     float f;
// };
type foo struct {
    data [4]byte
}

func (f foo) i() int32 {
    return int32(f.data)
}

func (f foo) setI(i int32) {
    f.data = [4]byte(b)
}

func (f foo) f() float32 {
    return float32(f.data)
}

func (f foo) setF(f float32) {
    f.data = [4]byte(b)
}

// Read a foo from r into data
func readFoo(r io.Reader, order binary.ByteOrder, data *foo) error {
    b := make([]byte, 4)
    if _, err := io.ReadFull(r, b); err != nil {
        return err
    }

    *data = foo{data: [4]byte(order.PutUint32(b))}
    return nil
}

// Write a foo from data into w
func writeFoo(w io.Writer, order binary.ByteOrder, data foo) error {
    b := make([]byte, 4)
    order.PutUint32(b, uint32(data))
    _, err := w.Write(b)
    return err
}