Iterate through a hierarchical list of infinite child elements

Example that flattens a nested and, possibly infinite, hierarchical list of child elements.


    class Program
    {
        static void Main(string[] args)
        {
            // Create dummy categories - not especially pretty
            var categories = new List();
            categories.AddRange(new List()
                                    {
                                        new Category(){ Id = 1, Name = "Cat1", Children = new List()
                                                                                              {
                                                                                                  new Category(){ Id = 101, Name = "Subcat1"},
                                                                                                  new Category(){ Id = 102, Name = "Subcat2"},
                                                                                                  new Category(){ Id = 103, Name = "Subcat3WithChildren", Children = new List()
                                                                                                                                                                         {
                                                                                                                                                                             new Category() { Id = 10301, Name = "Subcat1-sub1" },
                                                                                                                                                                             new Category() { Id = 10302, Name = "Subcat1-sub2" }
                                                                                                                                                                        }
                                                                                                                }
                                                                                              }},
                                        new Category() { Id = 2, Name = "Cat2"}
                                    });

            // Flatten the nesteded list of *child* categories
            var flatCategories = new List();
            foreach (var rootCategory in categories)
                flatCategories.AddRange(IterateChildCategories(rootCategory));

            // Spit out the results
            foreach (var cat in flatCategories)
                Console.WriteLine(cat.Name);

            Console.ReadKey();

        }

        /// 
        /// Iterates through a list of child categories. 
        /// 
        /// 
        /// Note that this skips the parent categories, and focusses only on the children.
        /// 
        private static IEnumerable IterateChildCategories(Category parent)
        {
            if (parent.Children == null) yield break;

            foreach (var g in parent.Children)
            {
                yield return g;

                foreach (var sub in IterateChildCategories(g))
                    yield return sub;
            }
        }

        public class Category
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public List Children { get; set; }

            public Category()
            {
                this.Children = new List();
            }
        }
    }