Kris' blog - Testing upon Nullable types in C# 2.0

Wednesday, June 28, 2006

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Most people that use C# are quite familiar with the if() expression and the (?:) conditional/ternary operator. In C# 2.0, the Visual C# team introduced another operator that's less known: the ?? or null coalescing operator. A quick demo explains how to use it. The result can be seen in Figure 1:

    1 using System;
    2 using System.Collections.Generic;
    3 using System.Text;
    4 
    5 namespace ConsoleApplicationNullableTypes
    6 {
    7     class Program
    8     {
    9         static void Main(string[] args)
   10         {
   11             int? input = null;
   12 
   13             IfStatements(input);
   14 
   15             // Now fill up the nullable input with some value.
   16             input = 99999;
   17 
   18             IfStatements(input);
   19 
   20             Console.ReadLine();
   21         }
   22 
   23         /// <summary>
   24         /// Show the 3 different ways to write the same if functionality in C# 2.0.
   25         /// </summary>
   26         /// <param name="input"></param>
   27         private static void IfStatements(int? input)
   28         {
   29             int result;
   30             // Scenario 1, normal if statement
   31             if (input.HasValue)
   32                 result = input.Value;
   33             else
   34                 result = 200;
   35 
   36             Console.WriteLine("Scenario 1, result: " + result.ToString());
   37 
   38             // Scenario 2, using the conditional/ternary operator
   39             result = input.HasValue ? input.Value : 200;
   40 
   41             Console.WriteLine("Scenario 2, result: " + result.ToString());
   42 
   43             // Scenario 3, using the null coalescing operator new to C# 2.0.
   44             result = input ?? 200;
   45 
   46             Console.WriteLine("Scenario 3, result: " + result.ToString());
   47             Console.WriteLine();
   48         }
   49     }
   50 }

The 3 different manners of writing the same test. Scenario 1, line number 31, is the normal if statement. Scenario 2 uses the conditional/ternary operator and just like in scenario 1 the new method HasValue is used to check if the nullable type has a value. If so then one could fetch the value by using the Value property on the nullable type.
Scenario 3, line number 44, uses the new null coalescing operator which is only available in C# 2.0.

Since I started developing with C# 2.0 in May 2005 I used to use the code like described in scenario 2 until I found out about the null coalescing operator. I find it easier to read and to use in my code. But because I found out that not too many people seem to be aware of this new gem in the C# 2.0 language I wanted to show it off in an article.

Figure 1: The result of the test.