泛型的性能优势

 最近在看《CLR via C#》，有关泛型的优势，感觉说的挺不错的特记录一下，以供以后查看。

    泛型为开发人员提供的优势：

1. 源代码保护
2. 类型安全
3. 更清晰的代码
4. 更佳的性能

为了理解泛型的优势，写了一个程序来比较泛型List算法和FCL的非泛型ArrayList算法的性能。同时使用值类型和引用类型的对象来测试这两个算法的性能：

static void Main(string[] args){ValueTypePerfTest();ReferenceTypePerfTest();Console.ReadLine();}public static void ValueTypePerfTest(){const Int32 count = 10000000;using (new OperationTimer("List<Int32>")){List<Int32> l = new List<Int32>(count);for (Int32 i = 0; i < count; i++){l.Add(i);Int32 x = l[i];}l = null;}using (new OperationTimer("ArrayList of Int32")){ArrayList a = new ArrayList();for (Int32 i = 0; i < count; i++){a.Add(i);Int32 x = (Int32)a[i];}a = null;}}public static void ReferenceTypePerfTest(){const Int32 count = 10000000;using (new OperationTimer("List<string>")){List<string> l = new List<string>();for (Int32 i = 0; i < count; i++){l.Add("X");string x = l[i];}l = null;}using (new OperationTimer("ArrayList of string")){ArrayList a = new ArrayList();for (Int32 i = 0; i < count; i++){a.Add("X");string x = (String)a[i];}a = null;}Console.ReadLine();}}internal sealed class OperationTimer : IDisposable{private Int64 m_startTime;private string m_text;private Int32 m_collectionount;public OperationTimer(string text){PrepareForOperation();m_text = text;m_collectionount = GC.CollectionCount(0);m_startTime = Stopwatch.GetTimestamp();}public void Dispose(){Console.WriteLine("{0,6:###.00} seconds (GCs={1,3})  {2}",(Stopwatch.GetTimestamp()-m_startTime)/(Double)Stopwatch.Frequency,GC.CollectionCount(0)-m_collectionount,m_text);}private static void PrepareForOperation(){GC.Collect();GC.WaitForPendingFinalizers();GC.Collect();}

输出结果如下：

    这个输出结果证明：将泛型list算法应用于Int32类型，速度比将非泛型ArrayList算法应用于Int32快的多，用ArrayList来操作值类型（Int32），会造成大量装箱操作，最终要进行44次垃圾回收次数（GC）。相应地，List算法需要的垃圾回收次数是0。使用引用类型来测试，差别就没有那么明显了。