<?php
class Test
{
    private $props = ['a' => 'text', 'b' => 1];

    public function &__get($prop)
    {
        return $this->props[$prop];
    }

    public function __set($prop, $value)
    {
        if ($prop === 'b') $value = [$value];
        $this->props[$prop] = $value;
    }

    public function getProperties()
    {
        return [$this->props];
    }
}

$obj = new Test;
$obj->b = $obj->b;
print_r($obj->getProperties());
?>