#1,196 – Using Fluent-Style Syntax when Chaining Iterators

You can chain iterator code together using a fluent-style syntax if you define extension methods for the corresponding IEnumerable<T> type that you’re using.  In the code below, we chain several iterators together, progressively filtering an IEnumerable<Dog> collection.

    class Program
        static void Main(string[] args)
            foreach (Dog d in AllMyDogs().YoungDogs().HerdingDogs())
                if (d.Breed == Breed.JackRussell)


        private static IEnumerable<Dog> AllMyDogs()
            yield return new Dog("Kirby", Breed.BorderCollie, 14);
            yield return new Dog("Jack", Breed.JackRussell, 15);
            yield return new Dog("Ruby", Breed.Mutt, 4);
            yield return new Dog("Lassie", Breed.Collie, 19);
            yield return new Dog("Shep", Breed.Collie, 2);
            yield return new Dog("Foofoo", Breed.Sheltie, 8);
            yield return new Dog("Pongo", Breed.Dalmatian, 4);
            yield return new Dog("Rooster", Breed.WestHighlandTerrier, 1);

    static class DogFilters
        public static IEnumerable<Dog> YoungDogs(this IEnumerable<Dog> dogs)
            foreach (Dog d in dogs)
                if (d.Age < 10)
                    yield return d;

        public static IEnumerable<Dog> HerdingDogs(this IEnumerable<Dog> dogs)
            foreach (Dog d in dogs)
                if ((d.Breed == Breed.BorderCollie) ||
                    (d.Breed == Breed.Collie) ||
                    (d.Breed == Breed.Sheltie))
                    yield return d;

Here’s the output:

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

6 Responses to #1,196 – Using Fluent-Style Syntax when Chaining Iterators

  1. Pingback: Dew Drop – October 3, 2014 (#1869) | Morning Dew

  2. This is super fun! I normally filter using lambda syntax, but it ends up looking quite ugly IMO:

    foreach (Dog d in AllMyDogs()
    .Where(dog => dog.Age youngDog.Breed == Breed.BorderCollie ||
    youngDog.Breed == Breed.Collie ||
    youngDog.Breed == Breed.Sheltie))

    I love the look of your code much more. For readability, it definitely seems well worth the effort to write out the extra methods the way you did! Thanks for this!

  3. Sean says:

    Thanks! Apologies if WordPress mangles your comments.

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