using System;

using System.Collections;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<int> list = new();

        list.Add(1);

        list.AddRange(new MyCollection<int>());

        Console.WriteLine($"list.Count: {list.Count}, list.Capacity: {list.Capacity}");

    }

​

    class MyCollection<T> : ICollection<T>

    {

        public int Count => Int32.MaxValue;

        public void CopyTo(T[] array, int arrayIndex) { } // Do nothing

​

        public bool IsReadOnly => throw new NotImplementedException();

        public void Add(T item) => throw new NotImplementedException();

        public bool Remove(T item) => throw new NotImplementedException();

        public void Clear() => throw new NotImplementedException();

        public bool Contains(T item) => throw new NotImplementedException();

        public IEnumerator<T> GetEnumerator() => throw new NotImplementedException();

        IEnumerator IEnumerable.GetEnumerator() => throw new NotImplementedException();

    }

​

}