泛型（一）

来源：互联网发布：魅影传说坐骑进阶数据编辑：程序博客网时间：2024/04/30 18:41

泛型（Generics）：一种代码重用（算法重用algorithm reuse）的机制。

使用泛型类型或方法时，用于指定类型的变量称为类型实参。（When defining a generic type or method, any variables it specifies for types (such as T) are called type parameters.）

泛型的优势
1）源代码保护（Source code protection）；
2）类型安全（Type safety）；
3）更清晰的代码（Cleaner code）；
4）更佳的性能（Better performance）:在用于值类型时，可减少装箱（boxing）与拆箱（unboxing），间接减少垃圾回收次数；减少代码中强制类型转换的次数（CLR无需验证这种转换是否安全）。

不足
1）调用特定数据类型方法时，CLR都会为该方法生成本机代码，这会增大应用程序的工作集（working set），从而损害性能。

using System;using System.Collections;using System.Collections.Generic;using System.Linq;using System.Text;using System.Diagnostics;namespace MyGenerics{    class Program    {        static void Main(string[] args)        {            ValueTypePerfTest();            ReferenceTypePerfTest();            Console.ReadKey();        }        private static void ValueTypePerfTest()        {            const int count = 100000000;            using (new OperationTimer("List<int>"))            {                List<int> list = new List<int>();                for (int n = 0; n < count; n++)                 {                    list.Add(n);     // No boxing                    int x = list[n]; // No unboxing                }                list = null; // Make sure this gets garbage collected            }            using (new OperationTimer("ArrayList of Int32"))            {                 ArrayList a = new ArrayList();                for (int n = 0; n < count; n++)                {                    a.Add(n);           // Boxing                    int x = (int)a[n];  // Unboxing                }                a = null; // Make sure this gets garbage collected            }        }        private static void ReferenceTypePerfTest()        {            const int count = 100000000;            using (new OperationTimer("List<string>"))            {                List<string> list = new List<string>();                for (int n = 0; n < count; n++)                {                    list.Add("X");      // Reference copy                    string x = list[n]; // Reference copy                }                list = null; // Make sure this gets garbage collected            }            using (new OperationTimer("ArrayList of string"))            {                ArrayList a = new ArrayList();                for (int n = 0; n < count; n++)                {                    a.Add("X");               // Reference copy                    string x = (string)a[n];  // Cast check & reference copy                }            }        }    }    // This class is useful for doing operation performance timing    internal sealed class OperationTimer : IDisposable    {        private Stopwatch m_stopwacth;        private string m_text;        private int m_collectionCount;        public OperationTimer(string text)        {            PrepareForOperation();            m_text = text;            m_collectionCount = GC.CollectionCount(0);            // This should be the last statement in this            // method to keep timing as accurate as possible            m_stopwacth = Stopwatch.StartNew();        }        public void Dispose()        {            Console.WriteLine("{0} (GCs={1,3} {2})", m_stopwacth.Elapsed,                GC.CollectionCount(0) - m_collectionCount, m_text);        }        private static void PrepareForOperation()        {            GC.Collect();            GC.WaitForPendingFinalizers();            GC.Collect();        }    }}

0 0