From the C# 2.0 Spec - very cool stuff!
Nullable types are constructed using the ? type modifier.
For example, int? is the nullable form of the predefined type int. A
nullable type’s underlying type must be a value type.
int? x = 123;
int? y = null;
if (x.HasValue) Console.WriteLine(x.Value);
if (y.HasValue) Console.WriteLine(y.Value);
Some examples of nullable conversions are shown in the
following.
int i = 123;
int? x = i; // int --> int?
double? y = x; // int? --> double?
int? z = (int?)y; // double? --> int?
int j = (int)z; // int? --> int
A new null coalescing operator, ??, is provided. The
result of a ?? b is a if a is non-null; otherwise, the result is b.
Intuitively, b supplies the value to use when a is null.
Console.WriteLine(s ?? "Unspecified");
...outputs the value of s, or outputs Unspecified if s is
null.
