How to specify parameter for generic list type extension method in c#

Question

Hi, I am trying to make an extension method that will shuffle the contents of a generic list collection regardless of its type however im not sure what to put in between the <..> as the parameter. do i put object? or Type? I would like to be able to use this on any List collection i have.

Thanks!

public static void Shuffle(this List<???????> source)
{
    Random rnd = new Random();

    for (int i = 0; i < source.Count; i++)
    {
        int index = rnd.Next(0, source.Count);
        object o = source[0];

        source.RemoveAt(0);
        source.Insert(index, o);
    }
}

Answer 1

You need to make it a generic method:

public static void Shuffle<T>(this List<T> source)
{
    Random rnd = new Random();

    for (int i = 0; i < source.Count; i++)
    {
        int index = rnd.Next(0, source.Count);
        T o = source[0];

        source.RemoveAt(0);
        source.Insert(index, o);
    }
}

That will allow it to work with any List<T>.

Answer 2

You just make your own method generic:

public static void Shuffle<T>(this List<T> source)

Answer 3

Slightly off-topic, but a Fisher-Yates shuffle will have less bias and better performance than your method:

public static void FisherYatesShuffle<T>(this IList<T> source)
{
    Random rng = new Random();

    for (int n = 0; n < source.Count; n++)
    {
        int k = rng.Next(n, source.Count);
        T tmp = source[k];
        source[k] = source[n];
        source[n] = tmp;
    }
}