gistfile1.cs

class Person
{
	public Person(string firstname, string lastname)
	{
		Firstname = firstname;
		Lastname = lastname;
	}

	public string Firstname { get; private set; }

	public string Lastname { get; private set; }

	public EmailAddress EmailAddress { get; private set; }

	public void ChangeEmailAddress(EmailAddress newEmailAddress)
	{
		if (newEmailAddress == null)
		{
			throw new ArgumentNullException("newEmailAddress");
		}

		if (newEmailAddress == EmailAddress)
		{
			return;
		}

		EmailAddress = newEmailAddress;
	}
}

class EmailAddress
{
	public static readonly EmailAddress Empty = new EmailAddress(string.Empty);

	private EmailAddress(string emailAddress)
	{
		Value = emailAddress;
	}

	public string Value { get; private set; }

	public static implicit operator string(EmailAddress emailAddress)
	{
		return emailAddress.Value;
	}

	public static implicit operator EmailAddress(string emailAddress)
	{
		return Parse(emailAddress);
	}

	public static EmailAddress Parse(string emailAddress)
	{
		if (!IsValid(emailAddress))
		{
			throw new FormatException(emailAddress);
		}

		return new EmailAddress(emailAddress);
	}

	public static bool TryParse(string emailAddress, out EmailAddress parsedEmailAddress)
	{
		try
		{
			parsedEmailAddress = Parse(emailAddress);

			return true;
		}
		catch (FormatException)
		{
			return false;
		}
	}

	public override string ToString()
	{
		return Value;
	}

	private bool IsValid(string emailAddress)
	{
		if (string.IsNullOrEmpty(emailAddress))
		{
			return false;
		}

		return emailAddress.Contains("@");
	}
}

/**
 * The code above makes this possible:
 * var person = new Person("Person", "People");
 *
 * // Implicit string to email address conversion.
 * person.ChangeEmailAddress("person@example.com");
 *
 * // Using the .ToString() override
 * Console.WriteLine(person.EmailAddress);
 *
 *
 * // Implicit email address to string conversion
 * string emailAddress = person.EmailAddress;
 *
 * Console.WriteLine(emailAddress);
 */