How to pass a database object to a class?

Question

PHP

Guys, I'm confused. There is a base App class to which the PDO database object must be passed. I have three solutions, but I’m even confused with the transfer, I don’t understand which one is better (correct), although they all work.
Option 1

class App{
  protected $db;
  public function __construct(){
    $this->db = new PDO('mysql:host=localhost;dbname=dbname', 'user', 'pass');
  }
}

Option 2

class App{
  protected $db;
  public function initDB(PDO $db){		
    $this->db = $d;
  }
}

class DB{
  public $db;
  public function instance(){
    $this->db = new PDO('mysql:host=localhost;dbname=dbname','user','pass');
    return $this->db;
  }
}

$app = new App();
$db = new DB();
$app->initDB($db->instance());

Option 3

class App{
  protected $db;
  public function initDB(PDO $db){
    $this->db = $d;
  }
}

class DB{
  public $db;
  public function __construct(){
    $this->db = new PDO('mysql:host=localhost;dbname=dbname','user','pass');
  }
}
$db = new DB();
$app = new App();
$app->initDB($db);

Answer 1

Classic DI

class App{
  protected $db;
  public function __construct($db){
    $this->db = $db;
  }
}

Answer 2

Why do you need an extra DB object? If it is needed only to initialize the connection to the database, then you are just wasting memory.
In fact, you've made a wrapper class over PDO. Although in the current implementation, I do not see any need for this.
I would not complicate what works without complication. What for to fence superfluous classes and objects??
Go from need. Need to control connection creation? - do initDB (), you do not need to control, and the object is always created when declaring App (), then the extra class is not needed.
As someone said: "to complicate is easy, to simplify is difficult." Don't make life difficult for yourself

Answer 3

<?
class App{
  protected static $_instance;

  private function __construct(){
    return new PDO('mysql:host=localhost;dbname=dbname','user','pass');
  }

  # Singlton methods
  public static function getInstance()
  {
    self::$_instance = self::$_instance ?? new self;
    return self::$_instance;
  }

  private function __clone() {}

  private function __wakeup() {}
}

# Init
App::getInstance();
?>

lifeexample.ru/php-primeryi-skriptov/php-singleton...

Answer 4

Option 2 is needed if an instance of the DB class will be used somewhere else besides App. And also, if the classes are slightly corrected, then you can make a LazyLoad connection to the database in the App class.