<?php
class 🌐sphere {}
class 🌏planet extends 🌐sphere {}

class Copernicus
{
    public 🌐sphere $gravity;
}

class Galileo extends Copernicus
{
    public 🌏planet $gravity;
}
?>
Fatal error: Type of Galileo::$gravity must be 🌐sphere (as in class Copernicus)



Property types are in-variant: