database singleton

/** Sample dog class */
class dog
{
    /** Creates new dog's instance */
    public function __construct() { echo 'aww aww <br/>'; }
}

$chappi = new dog();
$rex = new dog();

/** Sample dog class */
class dog
{
    public static $name = 'bob';
   
    /** Creates new dog's instance */
    public function __construct() { echo 'aww aww <br/>'; }
   
    /** Changes dog's name
     * @param string $name new dog's name     */
    public function change_name($name) { self::$name = $name; }
   
    /** Output's dogs name */
    public function say_name() { echo 'I am ', self::$name ,'<br/>'; }
}

$chappi = new dog();
$rex = new dog();

$chappi->change_name('chappi');

$chappi->say_name();
$rex->say_name();

/** Sample dog class */
class dog
{
    private static $the_dog = null;
   
    /** Creates new dog's instance */
    private function __construct() { echo 'NEW DOG created <br/>'; }

    /** Prevents creating an object by cloning */
    private function __clone() { }
       
    /** Returns singlton instance of a dog */
    public static function get_dog()
    {
        /*
         נבדוק האם יש משהו במשתנה המשותף
         אם אין — ניצור מופע חדש ונכניס אותו למשתנה המשותף
        כדי שהבאים אחרי יוכלו לבדוק את המשתנה הזה ולדעת האם
        כבר קיים מופע של המחלקה, או צריך ליצור אחד חדש
         */
        if( self::$the_dog === null)
        {
            self::$the_dog = new dog();
        }
        return self::$the_dog;
    }
}

$rex     = dog::get_dog();
$chompie = dog::get_dog();
$bob     = dog::get_dog();

/** Mysqli Wrapper */
class db extends mysqli
{
    private $connected = false;
    private static $instance = null;
   
    /** Returns singleton instance */
    public static function get_instance()
    {
        if (self::$instance === null)
        {
            self::$instance = new self('localhost', 'user', 'pass', 'base1');
        }
        return self::$instance;
    }
   
   
    /**
     * Performs MySQLI database connection
     * @param string $host the machine/host the database is located at
     * @param string $user database user
     * @param string $pass password for database user
     * @param string $db database's name
     * @param string $charset  connection collation charset
     */
    private function __construct($host, $user, $pass, $db, $charset = 'utf8')
    {
        parent::__construct($host, $user, $pass, $db);  
        if ($this->connect_error) die("Connection Error: ".$this->connect_error );
        $this->set_charset($charset);
        $this->connected = true;
    }

    /** Prevents creating an object by cloning */
    private function __clone() { }
   
    /**
     * Executes sql query against the database and handles failures
     * @param string $query the SQL to execute
     * @param int $resultmode MYSQLI_STORE_RESULT or MYSQLI_USE_RESULT
     * @return resource result to iterate or dies on error
     */
    public function query($query, $resultmode = MYSQLI_STORE_RESULT )
    {
        $res = parent::query($query, $resultmode);
        if($res === false) die("SQL Error: ".$this->error );
        return $res;
    }

    /** Closes the connection to the database */
    function __destruct()   {    if($this->connected) $this->close(); }
}

$db1 = db::get_instance();
$db2 = db::get_instance();

function do_something()
{
    $db3 = db::get_instance();
    $db3->query('SELECT `something` FROM `do`');
}