Value Object

Postcode.cs

public class Postcode
{
    private readonly string value;

    public Postcode(string value)
    {
        if (CheckPostcodeIsValid(value))
        {
            throw new InvalidPostcodeException();
        }

        this.value = value;
    }

    public static bool TryParse(string candidate, out Postcode postcode)
    {
        postcode = null;

        if (CheckPostcodeIsValid(candidate))
        {
            return false;
        }

        postcode = new Postcode(candidate.Trim().ToUpper());
        return true;
    }

    public static implicit operator string (Postcode postcode)
    {
        return postcode.value;
    }
    
    public override string ToString()
    {
        return this.value;
    }

    public override bool Equals(object obj)
    {
        var other = obj as Postcode;

        if (other == null)
        {
            return base.Equals(obj);
        }

        return object.Equals(this.value, other.value);
    }

    public override int GetHashCode()
    {
        return this.value.GetHashCode();
    }

    private static bool CheckPostcodeIsValid(string value)
    {
        var regex = new Regex(@"(GIR 0AA)|((([A-Z-[QVX]][0-9][0-9]?)|(([A-Z-[QVX]][A-Z-[IJZ]][0-9][0-9]?)|(([A-Z-[QVX]][0-9][A-HJKPSTUW])|([A-Z-[QVX]][A-Z-[IJZ]][0-9][ABEHMNPRVWXY])))) [0-9][A-Z-[CIKMOV]]{2})");
        var match = regex.Match(value);

        return match.Success;
    }
}