c# extension methods for generic array

I’m trying to make extension methods for generic array, so I could takeout random set of elements.
I made following extension methods for List<T> type and they work great, but I can’t work out how to do exactly the same for generic array:

public static T Random<T>(this List<T> list)
{
    return list[GameManager.instance.functions.RandomInt(list.Count - 1)];
}

public static IEquatable Random<IEquatable>(this List<IEquatable> list, List<IEquatable> hits)
{
    int rand = GameManager.instance.functions.RandomInt(list.Count - 1);
    while (hits.Exists(h => h.Equals(list[rand])))
        rand = GameManager.instance.functions.RandomInt(list.Count - 1);
    return list[rand];
}

public static List<T> Random<T>(this List<T> list, int count)
{
    List<T> result = new List<T>();
    for (int i = 0; i < count; i++)
    {
        result.Add(list.Random());
    }
    return result;
}

public static List<IEquatable> RandomUnique<IEquatable>(this List<IEquatable> list, int count)
{
    List<IEquatable> result = new List<IEquatable>();
    for (int i = 0; i < count; i++)
    {
        result.Add(list.Random(result));
    }
    return result;
}

I tried to rework the first method like this:

public static IEnumerable Random<IEnumerable>(this IEnumerable list)

but it doesn’t recognize list as an array so I can’t get to it’s length value.
I see a workaround, to do a List from Array, then get my random values and make array again, but it’s seems like too much action for just taking eg. 2 random from 4 elements array.
Please advise

>Solution :

Instead of implementing extensions methods for List<T>, T[] etc. you can try implementing a
single routine for IEnumerable<T>, e.g.

public static partial class EnumerableExtensions {
  public static T Random<T>(this IEnumerable<T> source) {
    //DONE: do not forget to validate public methods' arguments
    if (source is null)
      throw new ArgumentNullException(nameof(source));

    // If enumerable is a collection (array, list) we can address items explictitly
    if (source is ICollection<T> collection) {
      if (collection.Count <= 0)
        throw new ArgumentOutOfRangeException(nameof(source), 
          $"Empty {nameof(source)} is not supported.");

      return collection[GameManager.instance.functions.RandomInt(collection.Count - 1)];
    }

    // In general case we have to materialize the enumeration
    var list = source.ToList();

    if (list.Count <= 0)
      throw new ArgumentOutOfRangeException(nameof(source), 
        $"Empty {nameof(source)} is not supported.");

    return list[GameManager.instance.functions.RandomInt(list.Count - 1)];
  }
}

Then you can use the same extension method with list, array etc.:

// Array
int demo1 = new int[] {4, 5, 6}.Random();
// List
double demo2 = new List<double>() {1.0. 3.0}.Random(); 
// String is not array or list but implements IEnumerable<char>
char demo3 = "abcdef".Random();