php calling abstract static function from inside abstrac class

1abstract class AbstractFoo{
2    public static function foo() {
3        throw new RuntimeException("Unimplemented");
4    }
5    public static function getFoo(){
6        return static::foo();
7    }
8}
9
10class ConcreteFoo extends AbstractFoo{
11    public static function foo(){
12        return "bar";
13    }
14}
15
16echo ConcreteFoo::getFoo();
17