<?php
class foo {
    public $a1;
    public $a2 = array();
    public $a3;
    public $o1;
    public $o2;

    public function f1() {
        return $this->a1;
    }

    public function f2() {
        return $this->a2;
    }

    public function f3() {
        $this->a3 = array();
        return $this->a3;
    }

    public function f4() {
        return $this->o1;
    }

    public function f5() {
        $this->o2 = new stdClass;
        return $this->o2;
    }

    public function &f6() {
        return $this->a1;
    }

    public function f7(&$x) {
        $x = 2;
    }

}

$foo = new foo;

$foo->f1()[0] = 1;
var_dump($foo->a1);

$foo->f2()[0] = 1;
var_dump($foo->a2);

$foo->f3()[0] = 1;
var_dump($foo->a3);

try {
    $foo->f4()->a = 1;
} catch (Error $e) {
    echo $e->getMessage(), "\n";
}
var_dump($foo->o1);

$foo->f5()->a = 1;
var_dump($foo->o2);

$foo->a1[0] = 1;
$foo->f7($foo->f6()[0]);
var_dump($foo->a1[0]);
$foo->f1()[0]++;
var_dump($foo->a1[0]);
$foo->f6()[0]++;
var_dump($foo->a1[0]);
?>