PHP Value Objects

InvoiceNumber.php

<?php
namespace My\Namespace;

final class InvoiceNumber
{
    private $invoiceNumber;
    
    private function __construct(){};
    
    public static function fromString($string)
    {
      $invoiceNumber = new InvoiceNumber();
      $invoiceNumber->invoiceNumber = (string) $string;
      
      return $invoiceNumber;
    }
    
    public function getInvoiceNumber()
    {
      return $this->invoiceNumber;
    }
    
    public function equals(InvoiceNumber $invoiceNumber)
    {
      return $invoiceNumber->getInvoiceNumber === $this->getInvoiceNumber(); 
    }
}