Question

Is there any meaning to it?

public static function a(){

  static::_b();

}

private static function _b(){

}

static here is same as self in any situation, because you cannot override a private function in the child class, right?

Answer 1

As Germann Arlington said in the comment. A subclass can have it’s own implementation of _b() – even with a different visibility.

<?php
class Foo {
    public static function a() { static::_b(); }
    private static function _b() { echo 'Foo'; }
}

class FooEx extends Foo {
    public static function _b() { echo 'FooEx'; }
}

FooEx::a();

prints FooEx