Question

Consider this simple c# example:

var person = new Person {Name = "Fred", MailingAddress=null };
var result = String.Format("{0} lives at {1}",person.Name, person.MailingAddress.Street);

clearly this will throw a NullReferenceException because the MailingAddress proptery is null.

I could rewrite the second line as:

var result = String.Format("{0} lives at {1}", person.Name, person.MailingAddress == null ? (String)null : person.MailingAddress.Street);

Is there a simpler way to say express this?

Answer 1

There’s not really any good syntax for this. The coalesce operator is part of it, but you need to handle traversing through a null, not just replacing a null. One thing you could do would be to have a static “null object” for the class, something like:

public class Address 
{
  public static Address Null = new Address();
  // Rest of the class goes here
}

Then you could use the coalesce operator like so:

(person.MailingAddress ?? Address.Null).Street

If you want to go the extension method route, you could do something like this:

public static class NullExtension
{
    public static T OrNew<T>(this T thing)
        where T: class, new()
    {
        return thing ?? new T();
    }
}

Then you could do:

(person.MailingAddress.OrNew().Street)