Singleton Theory - PHP

Singleton design pattern ensures that the application creates only 1 object at run time. 
If it is necessary to use the same object many times in the application, we can prevent it from creating instances over and over again. We can achieve this by using static with singleton design pattern.

If the object has been created before, it continues its life through that object, if not, it continues its life by creating a new object.

In memory works via RAM.

It is recommended to create a private constructor.

class DbController
{
    private static $instance;
    public static $db;

    private function __construct()
    {
        $this->db = new PDO("mysql:host=localhost;dbname=***;", "root", "");
    }

    public static function getInstance()
    {
        if (!isset(self::$instance)) {
            self::$instance = new DbController;
        }
        return self::$instance;
    }

    public function dbConnection()
    {
        if (!isset(self::$db)) {
            self::$db = new PDO("mysql:host=localhost;dbname=***;", "root", "");
        }
        return self::$db;
    }
}

$cont1 = DbController::getInstance();
$cont2 = DbController::getInstance();
var_dump($cont1);
var_dump($cont2);
if ($cont1 === $cont2) echo 'Same';

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