MergeSort for C# (Optimized for Unity3D)

MergeSort.cs

using System;
using System.Collections.Generic;

internal static class MergeSort<T> {
	
	public static void Sort (List<T> list, Comparison<T> comparison) {
		if (list.Count <= 1)
			return;

		var mid = list.Count / 2;

		var left = GetList();
		var right = GetList();

		for (var i = 0; i < mid; ++i) {
			left.Add(list[i]);
		}
		for (var i = mid; i < list.Count; ++i) {
			right.Add(list[i]);
		}

		Sort(left, comparison);
		Sort(right, comparison);

		Merge(list, left, right, comparison);

		ReturnList(left);
		ReturnList(right);
	}

	private static void Merge (List<T> merged, List<T> left, List<T> right, Comparison<T> comparison) {
		merged.Clear();

		while (left.Count > 0 && right.Count > 0) {
			if (comparison(left[0], right[0]) > 0) {
				merged.Add(right[0]);
				right.RemoveAt(0);
			} else {
				merged.Add(left[0]);
				left.RemoveAt(0);
			}
		}
		for (var i = 0; i < left.Count; ++i) {
			merged.Add(left[i]);
		}
		for (var i = 0; i < right.Count; ++i) {
			merged.Add(right[i]);
		}
	}
	
	private static Queue<List<T>> listPool_ = new Queue<List<T>>();

	private static List<T> GetList () {
		if (listPool_.Count > 0) {
			var list = listPool_.Dequeue();
			list.Clear();
			return list;
		}
		return new List<T>();
	}

	private static void ReturnList (List<T> list) {
		listPool_.Enqueue(list);
	}

}

Usage.cs

List<ABSSequentiable> sequences = ...;

MergeSort<ABSSequentiable>.Sort(sequences, SortSequenceObjs);

static int SortSequencedObjs(ABSSequentiable a, ABSSequentiable b) {
	if (a.sequencedPosition > b.sequencedPosition) return 1;
	if (a.sequencedPosition < b.sequencedPosition) return -1;
	return 0;
}