#1,118 – foreach Works with Iterator Returned by yield

You can use the yield keyword in a method to implement an iterator.  The method in which it is defined returns an IEnumerable or IEnumerator.  The resulting iterator can be consumed using the foreach statement.

Below is an example of a method that returns an IEnumerable<T> which can then be iterated upon using a foreach statement.

        static IEnumerable<Dog> DogsWithKids(IEnumerable<Dog> dogList)
            foreach (Dog d in dogList)
                yield return d;
                yield return new Dog(d.Name + " Jr.",
                                     Math.Max(d.Age - 3, 1));

        static void Main(string[] args)
            List<Dog> myDogs = new List<Dog>
                    new Dog {Name = "Kirby", Age = 15},
                    new Dog {Name = "Ruby", Age = 2}

            // Iterate through dogs w/offsprings
            foreach (Dog d in DogsWithKids(myDogs))


The result is a sequence with twice as many elements as the original List<T>.



About Sean
Software developer in the Twin Cities area, passionate about software development and sailing.

2 Responses to #1,118 – foreach Works with Iterator Returned by yield

  1. Pingback: Dew Drop – June 16, 2014 (#1798) | Morning Dew

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