C#中使用泛型對比使用通用基礎類型效率降低近一倍

C#中使用泛型對比使用通用基礎類型效率降低近一倍

下面是測試結果：

CSharp class and generic TotalMilliseconds: 270772.9229
CSharp generic TotalMilliseconds: 269963.3999
CSharp normal TotalMilliseconds: 159716.9094

測試代碼：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static class InsertionSort where T : IComparable
        {
            public static void Sort(T[] a)
            {
                for (var i = 0 + 1; i <= a.Length - 1; i++)
                {
                    var tmp = a[i];
                    int j = i;

                    while (j > 0 && a[j - 1].CompareTo(tmp) > 0)
                        a[j] = a[--j];

                    a[j] = tmp;
                }
            }
        }

        public static void CSharpInsertionSortGeneric(T[] a) where T : IComparable
        {
            for (var i = 0 + 1; i <= a.Length - 1; i++)
            {
                var tmp = a[i];
                int j = i;

                while (j > 0 && a[j - 1].CompareTo(tmp) > 0)
                    a[j] = a[--j];

                a[j] = tmp;
            }
        }

        public static void CSharpInsertionSort(int[] a)
        {
            for (var i = 0 + 1; i <= a.Length - 1; i++)
            {
                var tmp = a[i];
                int j = i;

                while (j > 0 && a[j - 1].CompareTo(tmp) > 0)
                    a[j] = a[--j];

                a[j] = tmp;
            }
        }

        static void Main(string[] args)
        {
            DateTime start = DateTime.Now;
            int[] a = new int[200000];
            for (int i = 0; i < 200000; i++)
            {
                a[i] = 100 - i;
            }
            InsertionSort.Sort(a);
            DateTime end = DateTime.Now;
            Console.WriteLine(string.Format("CSharp class and generic TotalMilliseconds: {0}", (end - start).TotalMilliseconds));

            int[] a2 = new int[200000];
            for (int i = 0; i < 200000; i++)
            {
                a2[i] = 100 - i;
            }
            CSharpInsertionSortGeneric(a2);
            DateTime end2 = DateTime.Now;
            Console.WriteLine(string.Format("CSharp generic TotalMilliseconds: {0}", (end2 - end).TotalMilliseconds));

            int[] a3 = new int[200000];
            for (int i = 0; i < 200000; i++)
            {
                a3[i] = 100 - i;
            }
            CSharpInsertionSort(a3);
            DateTime end3 = DateTime.Now;
            Console.WriteLine(string.Format("CSharp normal TotalMilliseconds: {0}", (end3 - end2).TotalMilliseconds));


            //Console.WriteLine(String.Join(" ", a));
            Console.ReadKey();
        }
    }
}

很顯然，泛型降低了效率但提高了靈活性。

但是從MSDN上https://msdn.microsoft.com/en-us/library/ms172192.aspx 看到泛型有個有優點：

Better performance. Generic collection types generally perform better for storing and manipulating value types because there is no need to box the value types.

性能很好？很懷疑這不是每種情況下都是性能很好！為什麼會這樣？可能是運行時泛型會做更多的內存操作由此產生了效率的降低。