Chapter 4. Saying nothing with nullable types

Nullity is a concept that has provoked debate over the years. Is a null reference a value, or the absence of a value? Is “nothing” a “something”? Should languages support the concept of nullity at all, or should it be represented in other patterns?

In this chapter, I’ll try to stay more practical than philosophical. First we’ll look at why there’s a problem at all—why you can’t set a value type variable to null in C# 1 and what the traditional alternatives have been. After that, I’ll introduce you to our knight in shining armor—System.Nullable<T>—and then we’ll look at how C# 2 makes working with nullable types simple and compact. Like generics, nullable types sometimes have uses beyond what you might expect, and we’ll look at a few examples of these at the end of the chapter.

So, when is a value not a value? Let’s find out.

4.1. What do you do when you just don’t have a value?

The C# and .NET designers don’t add features just for kicks. There has to be a real, significant problem that needs fixing before they’ll go as far as changing C# as a language or .NET at the platform level. In this case, the problem is best summed up in one of the most frequently asked questions in C# and .NET discussion groups:

4.2. System.Nullable<T> and System.Nullable

4.3. C# 2’s syntactic sugar for nullable types

4.4. Novel uses of nullable types

4.5. Summary