Late static binding in PHP

Interesting nugget of PHP behaviour I was not aware of. Check it out.

In static inheritance, when calling a parent method that itself calls other statically defined methods using self::, those calls reference method from parent class, even though we might have them overridden in our derived class.

Late static binding tries to fix this by introducing a way for those calls to reference method from derived class, if available, by calling them with static:: (instead of self);

Example:

class A {
	public function name() {
		echo __CLASS__;
	}

	public static function self_call() {
		return self::name();
	}

	public static function static_call() {
		return static::name();
	}
}

class B extends A {
}

B::self_call(); // A
B::static_call(); // A

As expected, we get A both times, since we don’t have anything in our B class. Now, if we override name method, in our B class, behaviour changes a bit.

class A {
	public static function name() {
		echo __CLASS__;
	}

	public static function self_call() {
		return self::name();
	}

	public static function static_call() {
		return static::name();
	}
}

class B extends A {
    public static function name() {
		echo __CLASS__;
	}
}

B::self_call(); // A
B::static_call(); // B

This is where late static binding comes to play - using the static::name() we’re binding the name method at runtime, to derived class B.

That was the saltiest thing I ever tasted! And I once ate a big heaping bowl of salt!

– Phillip J. Fry