/// <summary>
/// 無限リスト
/// </summary>
/// <typeparam name="T"></typeparam>
class InfiniteList<T> : IEnumerable<T>
{
    private readonly List<T> _list;

    public InfiniteList(IEnumerable<T> source)
    {
        _list = source.ToList();
    }

    public IEnumerator<T> GetEnumerator()
    {
        while (true)
        {
            foreach (T val in _list)
            {
                yield return val;
            }
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }
}

class Program
{
    static void Main(string[] args)
    {
        // 繰り返しな無限リスト
        int[] a12345 = new[] { 1, 2, 3, 4, 5 };
        InfiniteList<int> infiniteInt = new InfiniteList<int>(a12345);
        foreach(var x in infiniteInt.Take(20))
        {
            Console.WriteLine(x);
        }

        // ランダムな無限リスト
        var rnd = new Random();
        Func<int>[] r = new Func<int>[] { () => rnd.Next() };
        InfiniteList<Func<int>> infiniteFunc = new InfiniteList<Func<int>>(r);
        foreach(var x in infiniteFunc.Take(20))
        {
            Console.WriteLine(x());
        }
    }
}