<?php

interface ISingleton {

    public static function getInstance(): ISingleton;
}

abstract class Singleton implements ISingleton {

    private static $_instances = array();

    private function __construct () {}
    private function __clone() {}

    public static function getInstance() : ISingleton {

        $className = get_called_class();
        self::$_instances[$className] = self::$_instances[$className] ?? new static();
        return self::$_instances[$className];
    }

}

class Person extends Singleton {

    public $age = 0;
}

class Man extends Person {

}

class Woman extends Person {

}

$person1 = Person::getInstance();
$person1->age = 1;
$man1 = Man::getInstance();
$man1->age = 2;
$woman1 = Woman::getInstance();
$woman1->age = 3;

var_dump($person1, $man1, $woman1, Person::getInstance(), Man::getInstance(), Woman::getInstance());