gistfile1.txt

<?php

class number
{
  private $value = 0;
  
  public function addNumber(number $number)
  {
    return $number->add($this->value);
  }
  
  public function add($value)
  {
    return new self($this->value + $value); // Is it east oriented? Seems that only void, self and boolean are ok as return value…
  }
}