class flexibleAccess{

  var $dbName = 'mydatabase';
	
class flexibleAccess{

      var $dbName = $_SESSION['mydatabase'];
	
class flexibleAccess{

   private $dbName;

   function __construct() {
         $this->dbName = $_SESSION['mydatabase'];
   }
}
	
constant("DBNAME", 'mydatabase');
	
require_once 'dbconfig.php';

class flexibleAccess {
  private $dbname;

  // set the default database name to the constant DBNAME
  // but allow override
  public function __construct ( $dbname = DBNAME )
  {
    $this->dbname = $dbname;
  }
}
	
require_once 'flexibleaccess.php';

$db = new flexibleaccess();
	
<?php
$login = new flexibleAccess();
$login->dbName = $_SESSION['mydatabase'];
?>