如何在PHP中设置变量类型

Question

I created a class MySQLConnector with the field connection. I have a connect function that can set the $this->connection variable:

public function connect($host, $user, $password, $database)
{
    $mysqli = new mysqli($host, $user, $password, $database);

    if(!$mysqli->connect_errno)
        $this->connection = $mysqli;
}

The problem is: $this->connection isn't a mysqli type. It doesn't have a type. How can I cast or set the type correctly? I want to use $this->connection->query(). In other places of this class and from outside of this class.

Answer 1

You could, for example user PDO instead of mysqli for its benefits. Or, you could simiply typecast like

public function setMysqli(mysqli $mysqli) {
    $this->mysqli = $mysqli;
}

A better way around would be to have those kind of stuff in the constructor as it is initialization:

class MySQLConnector implements DatabaseConnector {

    private $connection;

    /**
     * Initialize connector instance.
     * Not using OO API of mysqli here because it's junk anyways - you should use PDO.
     * @param $host The host of the SQL server.
     * @param $username The user for the database.
     * @param $password The password of the user.
     * @param $database The database to be used.
     * @throws RuntimeException if connection fails.
     */
    public function MySQLConnector($host, $username, $password, $database) {
        if (!$this->connection = mysqli_connect($host, $username, $password, $database)) {
            throw new RuntimeException(mysqli_connect_error());
        }
    }

    /**
     * Retrieve the connection reference for use.
     * The field $connection will always be a valid mysqli instance since
     * it is already initialized by the constructor.
     * @return A connection handle to the database for use with persistence operations.
     */
    public function getConnection() {
        return $this->connection;
    }

}