di.php

<?php

// fix this error please

class DBConnection
{

    private $connection;

    public function __construct($connection)
    {
        $this->connection = $connection;
    }

    public function connect()
    {
        echo sprintf("Connecting to %s", $this->connection);
    }
}

class MysqlConnection
{

    private $connection = "mysql";
}

class PgsqlConnection
{

    private $connection = "pgsql";
}

function connect(DBConnection $connection)
{
    $connection->connect();
}

connect(new MysqlConnection()); // Connecting to mysql
echo "<br />";
connect(new PgsqlConnection()); // Connecting to pgsql