using System;

using System.Linq;

using System.Collections.Generic;

​

public class SomeStrangeCollectionType<T>

{

    private List<T> _myList = new List<T>();

    public void Gibberish(T value)

    {

        _myList.Add(value); 

    }

    public T[] ToArray()

    {

        return _myList.ToArray();   

    }

}

public class Program

{

    public static T Convert<T, TArray>(IEnumerable<TArray> src, Action<T, TArray> addMethod) where T : new()

    {

        var myType = (T)Activator.CreateInstance(typeof(T));

        foreach (var element in src)

            addMethod(myType, element);

        return myType;

    }

    public static void Main()

    {

        int[] src = { 4, 5, 6 };

        var stack = Convert<Stack<int>, int>(src, (lst, i) => lst.Push(i) );

        var strange = Convert<SomeStrangeCollectionType<int>, int>(src, (c, i) => c.Gibberish(i));

        Console.WriteLine(string.Join(",", stack.ToArray()));

        Console.WriteLine(string.Join(",", strange.ToArray()));

    }

}