May 2. 2008 21:41

I'd prefer just to have the null coalesce operator be expanded to mean "if ANYTHING to the left of me, evaluated from the left to the right, is null, then return what is to the right of me."

That doesn't change the existing behavior, and doesn't require any new syntax.

Now, could it be accomplished without taking the easy route and catching a NRE in the IL?

Will

May 2. 2008 21:41

It is possible to do this in C# 3.0 by using extension methods (see blogs.msdn.com/.../...methods-on-null-objects.aspx for details).

Golo Roden

May 2. 2008 21:42

Something like that would come in handy, but also maybe you shouldn't be violating the Law of Demeter so much that something like this would be that useful

Chad Myers

May 2. 2008 21:42

Interesting idea. The example can be considered a little bit extreme for completely obliterating the Law of Demeter (http://c2.com/cgi/wiki?LawOfDemeter), which helps avoid this type of code to begin with.

Sergio Pereira

May 2. 2008 21:43

Yes! Yes! Yes! I've been in the same situation, and I've even complained to co-workers that there should be a better way. I should have posted about it.

superjason

May 2. 2008 21:43

Great suggestion, I've suffered with this kind of issue as well. It's especially prevalent when using LINQ to SQL and you want to return an anonymous object that is built from a LEFT JOIN query.

Denny Ferrassoli

May 2. 2008 21:43

That is a good one mate, however it will only make a difference at the code readability level, no difference at all to the performance of execution or efficiency of the code execution.

But it is a good one to have. Hopefully Microsoft is listening to you!!!

Thanks,
Kaushik

Kaushik R

May 2. 2008 21:44

Interesting idea. How would you express a case where you wanted to nest the construct inside of a property access chain? E.g., in this situation:

Staff.Manager.PersonalDetails.??{Address}.Location.Postcode

Address is potentially null. I want to abort the property chain access in favor of the default value when Address is null, but I maintain that if is isn't null, it must contain a non-null Location reference.

Seems like things could get pretty ugly pretty quickly. Even if the operator is terse, there is still a lot of interpretation that the reader must do in a chain that long. Whereas to something like this:

string postCodeValue = null;
try
{
postCodeValue = Staff.Manager.PersonalDetails.Address.Location.Postcode
}
catch
{
postCodeValue = "No postcode";
}

while not an optimal implementation is a more readable form of the same effect.

Another alternative would be to return "Null Implementations" instead of null references when a property has no value. That is, return a valid object reference that is a do-nothing or default-value implementation instead of null.

I wonder if there isn't a way to accomplish your operator using extension methods and lambas ... something like a Coalesce() implementation that could abstract property access.

beefarino

May 2. 2008 21:45

I would argue that the best way to ensure that you don't get a null reference in an object hierarchy such as the one you presented would be to handle it in the code for each object in the hierarchy, i.e. to ensure that the Location object doesn't ever have a null Postcode field/property, etc. You could do it in C# or you could try doing as part of a Spec# contract.

Randolpho

May 2. 2008 21:45

I like it. Code debris like the frequent null checks we have to do is only getting in our way and wasting our time.

Brent

May 2. 2008 21:45

Thanks a lot for posting this article. It's an interesting read and a great help as well as learning. Keep posting nice articles like these. Thanks a ton.

Kaushik R

May 2. 2008 21:46

You could use this technique to do the same :
blogs.msdn.com/.../...-i-m-just-a-little-slow.aspx

This is not as easy to write as your suggested way for writing it, but it does the trick.

Jerome

Jerome Laban

May 2. 2008 21:46

I agree completely - an operator with the functionality you described would make the code much more elegant. Some may avoid the use because of code readability but I personally like the ?? and ?: operators.

Jerry

May 2. 2008 21:46

Not that what you propose would not be useful, but if you are accessing objects that deep then you are certainly violating the law of demeter (or principle of least knowledge) and are potentially creating some very brittle software. If you truly do have a need for accessing variables like that, then I would suggest looking into the "Null Object" pattern which may give you a few good ideas for how to create "Null objects" in your domain model so that you don't need to check for null references. Hope this helps!

Justin Etheredge

May 2. 2008 21:47

Maybe I'm missing the point, but... Staff.Manager.PersonalDetails.Address.Location.Postcode - that is code I would never allow a developer to write. The need to do that looks like violation of SRP. Either way, something like the Maybe monad in Haskell for C#...Functional programmers beating the crap out of C# to the front! Woops, just see from the link above that the guy does something like that. GRReat! I'd say, enough language extensions, expand the libraries instead...

Frank Quednau

May 2. 2008 21:47

I really don't think that is desirable. The syntax is tough to read and alien from most other operators (I know, that's not the point, sorry . This is also a somewhat too specific operation in my opinion, both the ? and ?? operators solve small common problems.

Also, in most cases you wouldn't have to check all the way through. There'd usually be business rules stating that a Manager will always have personal details, allowing you to skip that check - you get the point. I'm not saying that's always the case, but it just adds up to my thinking that this is a case so rare that there is no reason for an operator to do this specific task.

Alternatively you could solve this using a null object pattern.

Mark S. Rasmussen

May 2. 2008 21:48

Groovy has an operator like this.

http://groovy.codehaus.org/Operators

Joe

May 2. 2008 21:49

Take a look at themechanicalbride.blogspot.com/.../...n-c-30.html. It is describing how to implement a run-time macro in C# 3.0 by employing lambda expressions.

Kaveh Shahbazian

May 4. 2008 16:26

I would do it as
return ?(Staff.Manager.PersonalDetails.Address.Location.Postcode) ?? “No Postcode”;
so that first operator just returns null if anything is null, and then it is possible to select a value for null.

Andrey Shchekin