std.sql Level 2

int main(string[] args)
{
    IDatabaseFactory factory;

    if(args[0] == "MySQL")
        factory = new MySQLFactory();
    else
        factory = new PostreSQLFactory();

    updatePricelist(factory);
    return 0;
}

public interface IDatabase {
    //common database stuff
    alias open connect;
    public void open(string host, string db, string user, string pw);
    public void open(string host, string db, string user, string pw, const string[string] params);

    //alias close disconnect;
    //public void close();
    // exec(); prepare() etc...
}

public interface IDatabaseFactory {

   public  IDatabase createDatabaseInstance();
}

final class PostgreSQL : IDatabase {
    // common
    public void open(string host,string db,string user,string pw,
        const string[string] params) {

    }
    public void open(string host,string db,string user,string pw) {
    }
   //PostgreSQL specific
   public void funkyPGstuff() {}
}

final class PostreSQLFactory : IDatabaseFactory {

   public IDatabase createDatabaseInstance() {

      return new PostgreSQL();

   }
}

final class MySQL : IDatabase {
    // common
   public void open(string host,string db,string user,string pw,
        const string[string] params) {

    }
    public void open(string host,string db,string user,string pw) {
    }
   //MySQL specific
   public void funkyMySQLstuff() {}
}

final class MySQLFactory : IDatabaseFactory {
    public IDatabase createDatabaseInstance() {
        return new MySQL();
   }
}

// Update PriceList without knowing the database
void updatePricelist(IDatabaseFactory factory) {
    IDatabase db = factory.createDatabaseInstance();
    db.connect("localhost", "test", "bls", "secret");

    //db.exec("UPDATE ...");

}