PHP'de Immutable Value Object Pattern

final class Money {
    public function __construct(
        public readonly int $amount,
        public readonly string $currency,
    ) {}

    public function add(Money $other): self {
        if ($this->currency !== $other->currency) {
            throw new InvalidArgumentException('Para birimi uyuşmuyor');
        }
        return new self($this->amount + $other->amount, $this->currency);
    }

    public function equals(Money $other): bool {
        return $this->amount === $other->amount
            && $this->currency === $other->currency;
    }
}