C#中的通用Mergesort

我正试图在C#中实现一个通用的Mergesort算法，但我在Constraints方面遇到了困难。我已经搜索了很多参考文献，但我找不到任何像我这样实现算法的参考文献。

C#中的MergeSort算法

排序算法的通用实现

无论如何，我试图提供一种只允许用户对从IComparable接口继承的数据集进行Mergesort的实现。

以下是我到目前为止所拥有的：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SortUtil
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> testList = new List<int> { 1, 5, 2, 7, 3, 9, 4, 6 };
            Mergesort.mergeSort<int>(testList); // Compiler Error at this Line.
        }
    }
    class Mergesort
    {   
        public static void mergeSort<T>(ref List<T> inputData)
            where T: IComparable<T>
        {
            mergeSort(ref inputData, 0, inputData.Count - 1);
        }
        private static void mergeSort<T>(ref List<T> inputData, int firstIndex, int lastIndex)
            where T: IComparable<T>
        {
            // If the firstIndex is greater than the lastIndex then the recursion 
            // has divided the problem into a single item. Return back up the call 
            // stack.
            if (firstIndex >= lastIndex)
                return;
            int midIndex = (firstIndex + lastIndex) / 2;
            // Recursively divide the first and second halves of the inputData into
            // its two seperate parts.
            mergeSort(ref inputData, firstIndex, midIndex);
            mergeSort(ref inputData, midIndex + 1, lastIndex);
            // Merge the two remaining halves after dividing them in half.
            merge(ref inputData, firstIndex, midIndex, lastIndex);
        }
        private static void merge<T>(ref List<T> inputData, int firstIndex, int midIndex, int lastIndex)
            where T: IComparable<T>
        {
            int currentLeft = firstIndex;
            int currentRight = midIndex + 1;
            T[] tempData = new T[(lastIndex - firstIndex) + 1];
            int tempPos = 0;
            // Check the items at the left most index of the two havles and compare
            // them. Add the items in ascending order into the tempData array.
            while (currentLeft <= midIndex && currentRight <= lastIndex)
                if (inputData.ElementAt(currentLeft).CompareTo(inputData.ElementAt(currentRight)) < 0)
                {
                    tempData[tempPos++] = inputData.ElementAt(currentLeft++);
                }
                else
                {
                    tempData[tempPos++] = inputData.ElementAt(currentRight++);
                }
            // If there are any remaining items to be added to the tempData array,
            // add them.
            while (currentLeft <= midIndex)
            {
                tempData[tempPos++] = inputData.ElementAt(currentLeft++);
            }
            while (currentRight <= lastIndex)
            {
                tempData[tempPos++] = inputData.ElementAt(currentRight++);
            }
            // Now that the items have been sorted, copy them back into the inputData
            // reference that was passed to this function.
            tempPos = 0;
            for (int i = firstIndex; i <= lastIndex; i++) {
                inputData.Insert(firstIndex, tempData.ElementAt(tempPos));
            }
        }
    }
}

My issue:我在Program类的Main方法中遇到编译器错误；然而，当我静态调用mergeSort函数时，我不应该为它提供参数化类型吗？

我收到错误"The best overloaded method match for... has some invalid arguments."

我将非常感谢任何实施建议和/或任何纠正这一错误的方式。注意，我对Java最熟悉，因为C#不直接支持通配符，所以这种方法对我来说是陌生的。对此的任何解释都将不胜感激。

Mergesort.mergeSort(testList);

Mergesort.mergeSort<int>(ref testList);