Linq101-QueryExecution

 using System;
 using System.Linq;

 namespace Linq101
 {
     class QueryExecution
     {
         /// <summary>
         /// The following sample shows how query execution is deferred until the query is enumerated at a foreach statement.
         /// </summary>
         public void Linq99()
         {
             int[] numbers = new int[] { , , , , , , , , ,  };

             int i = ;

             //延迟执行
             var q = from n in numbers select ++i;

             foreach (int n in q)
             {
                 Console.WriteLine("n={0},i={1}", n, i);
             }
         }

         /// <summary>
         /// The following sample shows how queries can be executed immediately with operators such as ToList().
         /// </summary>
         public void Linq100()
         {
             int[] numbers = new int[] { , , , , , , , , ,  };

             int i = ;

             //ToList->立即执行
             var q = (from n in numbers select ++i).ToList();

             foreach (int n in q)
             {
                 Console.WriteLine("n={0},i={1}", n, i);
             }
         }

         /// <summary>
         /// The following sample shows how, because of deferred execution, queries can be used again after data changes and will then operate on the new data.
         /// </summary>
         public void Linq101()
         {
             int[] numbers = { , , , , , , , , ,  };

             //可重用
             var lowNumbers = from n in numbers
                              where n <=
                              select n;

             Console.WriteLine("First run numbers <=3:");
             foreach (int number in lowNumbers)
             {
                 Console.WriteLine(number);
             }

             lowNumbers = (from n in numbers select -n).ToArray();

             Console.WriteLine("Second run numbers <=3:");
             foreach (int number in lowNumbers)
             {
                 Console.WriteLine(number);
             }
         }
     }
 }