$this vs self vs static vs parent

$this

Refers to the current object instance within a class context. It is used to access non-static properties and methods. You cannot use it outside object context (e.g., in a static method).

class User {
    public $name = 'John';
    public function getName() {
        return $this->name;
    }
}

self

Refers to the current class (the class where it is written). It is used for static properties, static methods, and class constants.

class User {
    public static $count = 0;
    public function increment() {
        self::$count++;
    }
}

static (Late Static Binding)

Refers to the called class at runtime. It is used to access static properties or methods while considering class inheritance. Unlike self, static will resolve to the child class if the method was inherited and called from a child class.

class ParentClass {
    public static function who() {
        echo "ParentClass";
    }
    public static function test() {
        static::who(); // late static binding
        self::who();   // always ParentClass
    }
}

class ChildClass extends ParentClass {
    public static function who() {
        echo "ChildClass";
    }
}

ChildClass::test(); // output: ChildClass ParentClass

parent

Used to access methods, constants, or static properties of the parent class from within a child class.

class ChildClass extends ParentClass {
    public function __construct() {
        parent::__construct(); // call parent's constructor
    }
}