brainfuck.php

<?php
class Brainfuck
{
    public $ref;

    function &__get($x) {

        $this->ref = new class($this->ref) {

            private $p;

            function __construct(&$p) {
                $this->p = &$p;
            }

            function __isset($x) {
                $this->p = new Brainfuck;
                return false;
            }

            function __get($x) {

            }
            function __set($x, $y) {
                $this->$x = $y;
            }
        };
        return $this->ref;
    }
    function __set($x, $y) { /* not called */
        var_dump($x, $y);
    }
    function __isset($x) {
        return true;
    }
}

$a = new Brainfuck;
$a->b->c = $a->b->c  ?? 2;

$a->b->c ??= $b; 
isset($a->b) ? ( $_ = $a->b; $_->c ?? $_->c = $b ) : $a->b->c = $b;
var_dump($a);