public class Price : ValueObject
{
    public decimal Amount { get; set; }
    public string Currency { get; set; }

    public override IEnumerable<object?> GetAtomicValues()
    {
        return [Amount, Currency];
    }
}

public class UserName : SingleValueObject<string>
{
    public UserName(string value)
    {
        if (value.Length > 20)
            throw new Exception("Name is not valid!");

        Value = value;
    }
}

public class UserName : SingleValueObject<string>
{
    [MaxLength(20)]
    public override required string Value { get; init; }
}