When NOT to use yield (return) [duplicate]

Answer 1

What are the cases where use of yield will be limiting, unnecessary, get me into trouble, or otherwise should be avoided?

I can think of a couple of cases, IE:

• Avoid using yield return when you return an existing iterator. Example:

  // Don't do this, it creates overhead for no reason
  // (a new state machine needs to be generated)
  public IEnumerable GetKeys() 
  {
      foreach(string key in _someDictionary.Keys)
          yield return key;
  }
  // DO this
  public IEnumerable GetKeys() 
  {
      return _someDictionary.Keys;
  }
  

• Avoid using yield return when you don't want to defer execution code for the method. Example:

  // Don't do this, the exception won't get thrown until the iterator is
  // iterated, which can be very far away from this method invocation
  public IEnumerable Foo(Bar baz) 
  {
      if (baz == null)
          throw new ArgumentNullException();
       yield ...
  }
  // DO this
  public IEnumerable Foo(Bar baz) 
  {
      if (baz == null)
          throw new ArgumentNullException();
       return new BazIterator(baz);
  }