What's the difference between :: (double colon) and -> (arrow) in PHP?

Question

There are two distinct ways to access methods in PHP, but what\'s the difference?

$response->setParameter(\'foo\', \'bar\');

and

Answer 1

:: is used in static context, ie. when some method or property is declared as static:

class Math {
    public static function sin($angle) {
        return ...;
    }
}

$result = Math::sin(123);

Also, the :: operator (the Scope Resolution Operator, a.k.a Paamayim Nekudotayim) is used in dynamic context when you invoke a method/property of a parent class:

class Rectangle {
     protected $x, $y;

     public function __construct($x, $y) {
         $this->x = $x;
         $this->y = $y;
     }
}

class Square extends Rectangle {
    public function __construct($x) {
        parent::__construct($x, $x);
    }
}

-> is used in dynamic context, ie. when you deal with some instance of some class:

class Hello {
    public function say() {
       echo 'hello!';
    }
}

$h = new Hello();
$h->say();

By the way: I don't think that using Symfony is a good idea when you don't have any OOP experience.