Question

I have defined classes like Email,Url,Alphabet,Number and … just to centralize the validation logic needed for each of these objects , like :

public class Email
{
    private string value;
    private bool isValid;

    const string RegexPattern = @"^(?("")("".+?""@)|(([0-9a-zA-Z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-zA-Z])@))(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,6}))$";


        public Email(string address, int minLength = 8, int maxLength = 50)
        {
            value = address;

            isValid = Validator.IsValid(address,RegexPattern,minLength,maxLength);
        }

        public string Address
        {
            get
            {
                return value;
            }
        }

        public bool IsValid
        {
            get
            {
                return isValid;
            }
        }


}

can this be called a value object ?if not what it lacks ?

Answer 1

The implementation is one I would expect for a value object. It is immutable (though you may want to add readonly modifiers on the fields) and doesn’t seem to have its own identity.

You need to consider whether it is indeed a value object depending on the domain – that’s how you decide whether this should be a value object or not.