Koto

value object

public sealed class Email : ValueObject
{
    public string Value { get; }
    private Email(string value) => Value = value;

    public static Result<Email> Create(string value) =>
        string.IsNullOrWhiteSpace(value) ? Errors.General.ValueIsRequired() :
        value.Length > 150              ? Errors.General.InvalidLength(1, 150) :
                                          new Email(value);
}

aggregate root

public class Order : AggregateRoot<OrderId>
{
    public static Result<Order> Place(Customer customer, IReadOnlyList<OrderItem> items)
    {
        if (items.Count == 0)
            return OrderErrors.NoItems();

        var order = new Order(OrderId.New(), customer.Id);
        order.AddDomainEvent(new OrderPlacedDomainEvent(order.Id, customer.Id));
        return order;
    }

    public Result<Unit> Cancel(string reason)
    {
        if (Status == OrderStatus.Cancelled)
            return OrderErrors.AlreadyCancelled();

        Status = OrderStatus.Cancelled;
        AddDomainEvent(new OrderCancelledDomainEvent(Id, reason));
        return Unit.Value;
    }
}