Immutable classes - mutator function

mutator.php

<?php

final immutable class Currency {}
final immutable class Money {
  public $amount;
  public $currency;
  public function __construct(float $amount, Currency $currency) {
    $this->amount = $amount;
    $this->currency = $currency;
  }
  public transformer function withCurrency(Currency $currency) {
    $this->currency = $currency; // $this is newly created clone
    return $this;
  }
  public transformer function withAmount(float $amount) {
    $this->amount = $amount; // $this is newly created clone
    return $this;
  }
}

$eur = new Cuurency('EUR');
$usd = new Currency('USD');

$totalAmount = new Money(100, $eur);
$usdTotalAmount = $totalAmount->withCurrency($usd)->withAmount(150);