anonymous-class.php

<?php
class CoolDto
{
    public $master = 'admin';
    public $child;

    public function __construct()
    {
        $this->child = $this->createChildDto();
    }

    protected function createChildDto()
    {
        return new class() {
            public $x1 = 1;
            public $x2 = 2;
        };
    }
}

$x = new CoolDto();
$x->child->x1 += 80;
echo json_encode($x);

// output: {"master":"admin","child":{"x1":81,"x2":2}}