C#-扩展方法-Linq

密封类

sealed，无法被继承

var

可以定义匿名对象

static void test1()
{var t = 1;t = "jack";//报错，类型已经确定好了var s = new{id = 1,name = "tom"};Console.WriteLine(s.id + s.name);
}

扩展方法

对现有类型做方法的扩展，密封类也可以实现
不在同一命名空间需要引入，返回类型根据自己需要来决定

系统类型扩展

密封类扩展 

Linq 

static void Main(string[] args)
{test1();
}static void test1()
{int[] nums = { 1, 7, 2, 6, 5, 4, 9, 13, 20 };List<int> list = new List<int>(nums);var res = nums.Where(x => x % 2 == 1).Select(x => x * x).OrderByDescending(x => x);foreach (var item in res){Console.WriteLine(item);}
}

class Program
{static void Main(string[] args){test1();}static void test1(){Student s1 = new Student() { id = 1, name = "tom1" };Student s2 = new Student() { id = 1, name = "tom2" };Student s3 = new Student() { id = 2, name = "tom3" };List<Student> list = new List<Student>() { s1, s2, s3 };//根据id升序，id相同按照name降序var res = list.OrderBy(s => s.id).ThenByDescending(s => s.name);foreach (var item in res){Console.WriteLine(item.ToString());}//从1开始，按顺序生成10个数var num1 = Enumerable.Range(1, 10);//生成10个abcdvar num2 = Enumerable.Repeat("abcd", 10);foreach (var item in num1){Console.WriteLine(item);}foreach (var item in num2){Console.WriteLine(item);}}}