I believe some of you already know about this but for me I never used it. Yield keyword has been existed since .NET 2.0 so I decided to look up of what it does and try to understand it

Based on MSDN

Yield is used in an iterator block to provide a value to the enumerator object or to signal the end of iteration, it takes one of the following form

Based on my understanding

Yield is a concatenation for a collection, or in SQL we normally use UNION

Yield break; is used to exit from the concatenation (remember it is not used to skip !)

One practical sample that I can think of is to get the enumerable of exception from inner exception (e.g stack trace)

sample code

Code Snippet
  1. class Program
  2.     {
  3.         ///<summary>
  4.         /// simple function to return IEnumerable of integer
  5.         ///</summary>
  6.         ///<returns></returns>
  7.         private static IEnumerable<int> GetIntegers()
  8.         {
  9.             for (int i = 0; i <= 10; i++)
  10.                 yield return i;
  11.         }
  13.         ///<summary>
  14.         /// simple function to return collection of class
  15.         ///</summary>
  16.         ///<returns></returns>
  17.         private static IEnumerable<MyClass> GetMyNumbers()
  18.         {
  19.             for (int i = 0; i <= 10; i++)
  20.                 if (i > 5)
  21.                     yield break;
  22.                 else
  23.                     yield return new MyClass() { Number = i };
  24.         }
  26.         internal class MyClass
  27.         {
  28.             public int Number { get; set; }
  29.             public string PrintNumber
  30.             {
  31.                 get {
  32.                     return “This is no “ + Number.ToString();
  33.                 }
  34.             }
  35.         }
  37.         static void Main(string[] args)
  38.         {
  39.             Console.WriteLine(“Simple array of integer”);
  40.             foreach (var number in GetIntegers())
  41.                 Console.WriteLine(number.ToString());
  43.             Console.WriteLine();
  44.             Console.WriteLine(“Collection of classes”);
  45.             foreach (var myclass in GetMyNumbers())
  46.                 Console.WriteLine(myclass.PrintNumber);
  48.             Console.ReadLine();
  49.         }
  50.     }

Output

Simple array of an integer
0
1
2
3
4
5
6
7
8
9
10Collection of classes
This is no 0
This is no 1
This is no 2
This is no 3
This is no 4
This is no 5