Yield Return with Null

Question

Is there any way to optionally return a null with a "return yield" driven iterator?

I would like to return a null in some cases and I don't think this is particular to IEnumerable of type string. Same goes for IEnumerable of type int etc. Thanks

static void Main(string[] args) {     var Items = GetItems();      if (Items != null)     {         foreach (var item in Items)         {             Console.WriteLine(item);         }     }     else     {         Console.WriteLine("<null>");     } }  static IEnumerable<string> GetItems() {     if (false)     {         yield return "Andy";         yield return "Jennifer";     }      return null; // <- Compiler Error:     // Cannot return a value from an iterator.      // Use the yield return statement to return a value,     // or yield break to end the iteration. } 

Answer 1

If you need to things like that (or throw things like ArgumentException immediately), you need to separate your iterator into two methods:

 public IEnumerable<string> GetItems() {      if (something) return null;      return GetItemsInternal();  }   private IEnumerable<string> GetItemsInternal() {      // the actual iterator with "yield return" goes here.  } 

Answer 2

You're not using an enumerable as it was intended (to iterate objects in a collection). If you want to keep your code similar to what it is now, you should do something like this:

static void Main(string[] args) {     var Items = GetItems();      foreach (var item in Items) //this will not enter the loop because there are no items in the Items collection     {             Console.WriteLine(item);     }      //if you still need to know if there were items, check the Count() extension method     if(Items.Count() == 0)     {       Console.WriteLine("0 items returned");     }   }  static IEnumerable<string> GetItems() {     if (false)     {         yield return "Andy";         yield return "Jennifer";     }      yield break; }