Programming .NET 3.5

Extension Methods

LINQ is similar to SQL, so if you already know a little SQL the query expressions introduced in the previous sections should seem quite intuitive and easy to understand. However, as C# code is ultimately executed by the .NET CLR, the C# compiler has to translate the query expressions to a format that the .NET runtime understands. In other words, the LINQ query expressions written in C# must be translated into a series of method calls. The methods called are known as extension methods, and they are defined in a slightly different way than normal methods.

Example 9-5 is identical to Example 9-1, except it uses query operator extension methods instead of query expressions. The parts of the code that have not changed are omitted for brevity.

Example 9-5. Using query operator extension methods

using System;
using System.Collections.Generic;
using System.Linq;

namespace Programming_CSharp
{
   // Simple customer class
   public class Customer
   {
      // Same as in Example 9-1
   }

   // Main program
   public class Tester
   {
      static void Main()
      {
         List<Customer> customers = CreateCustomerList();

         // Find customer by first name
         IEnumerable<Customer> result =
             customers.Where(
                 customer => customer.FirstName == "Donna");
         Console.WriteLine("FirstName == \"Donna\"");
         foreach (Customer customer in result)
             Console.WriteLine(customer.ToString());
         Console.Read();
      }

      // Create a customer list with sample data
      private static List<Customer> CreateCustomerList()
      {
         // Same as in Example 9-1
      }
   }
}

Figure 9-6 ...