static void Main(string[] args)
        {
            var trainings = new TrainingsCollection <Training>();

            trainings.Add(new Training {
                Name = "C#", Cost = 10
            });
            trainings.Add(new Training()
            {
                Name = "Java", Cost = 10
            });

            // This loop with trigger to IEnumerator<T> GetEnumerator() from our custom TraningsEnumerator
            foreach (var item in trainings)
            {
                Console.WriteLine($"Traning Name {item.Name} and cost {item.Cost}");
            }

            Console.ReadKey();
        }
 public TraningsEnumerator(TrainingsCollection <T> collection)
 {
     this.collection = collection;
 }