<?php

class test {}
class Single {
    protected static $ins = null;

    public static function getIns()
    {
        if(self::$ins === null){
            self::$ins = new self();
        }
        return self::$ins;
    }

    final protected function __construct(){

    }

    final protected function __clone(){

    }
}

$a1 = Single::getIns();
$a2 = Single::getIns();
if($a1 === $a2) {
    echo '是同一个对象', PHP_EOL;
}else{
    echo '不是同一个对象', PHP_EOL;
}