di2.go

type Database interface {
    SaveData(data string) error
}

type MySQL struct {
    // fields and methods
}

func (m *MySQL) SaveData(data string) error {
    // code to save data to MySQL
}

type ProcessData struct {
    db Database
}

func (p *ProcessData) SaveData(data string) error {
    return p.db.SaveData(data)
}

func main() {
    db := &MySQL{}
    process := &ProcessData{db: db}
    process.SaveData("data")
}