C# in Depth

System.Nullable and System.Nullable117ToString on the value if there is. Equals is slightly more complicated—we’ll comeback to it when we’ve discussed boxing.Finally, two conversions are provided by the framework. First, there is an implicitconversion from T to Nullable. This always results in an instance where HasValuereturns true. Likewise, there is an explicit operator converting from Nullable toT, which behaves exactly the same as the Value property, including throwing an exceptionwhen there is no real value to return.NOTEWrapping and unwrapping—The C# specification names the process ofconverting an instance of T to an instance of Nullable wrapping, withthe obvious opposite process being called unwrapping. The C# specificationactually defines these terms with reference to the constructor takinga parameter and the Value property, respectively. Indeed these calls aregenerated by the C# code, even when it otherwise looks as if you’re usingthe conversions provided by the framework. The results are the sameeither way, however. For the rest of this chapter, I won’t distinguishbetween the two implementations available.Before we go any further, let’s see all this in action. Listing 4.1 shows everything youcan do with Nullable directly, leaving Equals aside for the moment.Listing 4.1Using various members of Nullablestatic void Display(Nullable x){Console.WriteLine ("HasValue: {0}", x.HasValue);if (x.HasValue){Console.WriteLine ("Value: {0}", x.Value);Console.WriteLine ("Explicit conversion: {0}", (int)x);}Console.WriteLine ("GetValueOrDefault(): {0}",x.GetValueOrDefault());Console.WriteLine ("GetValueOrDefault(10): {0}",x.GetValueOrDefault(10));Console.WriteLine ("ToString(): \"{0}\"", x.ToString());Console.WriteLine ("GetHashCode(): {0}", x.GetHashCode());Console.WriteLine ();}...Nullable x = 5;x = new Nullable(5);Console.WriteLine("Instance with value:");Display(x);x = new Nullable();Console.WriteLine("Instance without value:");Display(x);In listing 4.1 we first show the two different ways (in terms of C# source code) of wrappinga value of the underlying type, and then we use various different members on theLicensed to Rhona Hadida