C# 3.0 新特性

  C# 3.0 新增了一些激动人心的特性。本文通过一个控制台应用程序来展示 C# 3.0 相对于C#2.0 的所有的新特性。

using System;
using System.Collections.Generic;
using System.Linq;
 
namespace CS30NEW
{
    ///<summary>
    ///
    /// C#3.0新特性
    ///
    /// Blog:http://xianfen.net
    ///
    /// Author:飘遥(Zxjay)
    ///
    /// Date:2007-12-22
    ///
    /// Email:tda7264@163.com
    ///
    ///</summary>
    class Program
    {
        static void Main(string[] args)
        {
            /*
             * C#3.0新特性之自动属性(Automatic Properties)
             * 自动属性不能实现自定义类型及数据完整性检查
             * 保留了属性的其他优点
            */
            Console.WriteLine("C#3.0新特性之自动属性(Automatic Properties)");
 
            Test1 t1 = new Test1();
 
            t1.String1 = "http://xianfen.net";
            t1.Int1 = 0;
 
            Console.WriteLine(t1.String1 + "\n" + t1.Int1);
 
 
            /*
             * C#3.0新特性之对象初始化器(Object Initializers)
             */
            Console.WriteLine("\nC#3.0新特性之对象初始化器(Object Initializers)");
 
            Test1 t2 = new Test1 { String1 = "http://xianfen.net", Int1 = 0 };
 
            Console.WriteLine(t2.String1 + "\n" + t2.Int1);
 
 
            /*
             * C#3.0新特性之匿名类型(Anonymous Types)
             * 变量初始化后改变量的类型就确定了，如果再赋值其他类型将抛出异常
             */
            Console.WriteLine("\nC#3.0新特性之匿名类型(Anonymous Types)");
 
            var t3 = new Test1 { String1 = "http://xianfen.net", Int1 = 0 };
 
            Console.WriteLine(t3.String1 + "\n" + t3.Int1);
 
 
            /*
             * C#3.0新特性之集合初始化器(Collection Initializers)
             */
            Console.WriteLine("\nC#3.0新特性之集合初始化器(Collection Initializers)");
 
            List<Test1> l = new List<Test1>
            {
                new Test1{ String1 = "http://xianfen.net", Int1 = 0 },
                new Test1{ String1 = "http://www.xianfen.net", Int1 = 1 },
                new Test1{ String1 = "http://zxjay.cn", Int1 = 2 }
            };
 
            Console.WriteLine(l.Count);
            Console.WriteLine(l[0].String1 + "\n" + l[0].Int1);
 
 
            /*
             * C#3.0新特性之Lambda表达式(Lambda Expressions)
             */
            Console.WriteLine("\nC#3.0新特性之Lambda表达式(Lambda Expressions)");
 
            IEnumerable<Test1> e = l.Where(tst => tst.Int1 > 0);
 
            foreach (Test1 t in e)
            {
                Console.WriteLine(t.String1 + "\n" + t.Int1);
            }
 
 
            /*
             * C#3.0新特性之查询语法(Query Syntax)
             * 语法跟SQL类似，select 放在最后
             */
            Console.WriteLine("\nC#3.0新特性之查询语法(Query Syntax)");
 
            IEnumerable<Test1> e1 = from t in l where t.Int1 < 2 orderby t.String1 descending select t;
 
            foreach (Test1 t in e1)
            {
                Console.WriteLine(t.String1 + "\n" + t.Int1);
            }
 
 
            /*
             * C#3.0新特性之扩展方法(Extension Methods)
             * 有点类似于JavaScript的prototype
             * 实现扩展方法的类及扩展的方法都必须是静态的，待扩展的类作为参数，前面加this关键字
             * 扩展方法容易造成程序混乱，给维护和升级造成麻烦，如果不是非常必要，尽量不要使用
             */
            Console.WriteLine("\nC#3.0新特性之扩展方法(Extension Methods)");
 
            var t4 = new Test1 { String1 = "http://xianfen.net", Int1 = 0 };
 
            Console.WriteLine(t4.AddDefaultPage());
 
 
            Console.ReadKey();
        }
    }
 
    public class Test1
    {
        public string String1 { set; get; }
        public int Int1 { set; get; }
    }
 
    public static class Test2
    {
        /*
         * C#3.0新特性之扩展方法(Extension Methods)
         * 有点类似于JavaScript的prototype
         * 实现扩展方法的类及扩展的方法都必须是静态的，待扩展的类作为参数，前面加this关键字
         */
        public static string AddDefaultPage(this Test1 t)
        {
            return t.String1 + "/Default.aspx";
        }
    }
}

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