1 Lambda表达式1.1 Lambda 表达式1.1.1 创建委托或表达式树“Lambda 表达式”是一个匿名函数，它可以包含表达式和语句，并且可用于创建委托或表达式树类型。    class Program    {        static void Main(string[] args)        {            del myDelegate = x => x * x;            int j = myDelegate(5); //得到j = 25             Console.WriteLine(j);            Console.Read();        }    }    delegate int del(int i);    class Program    {        static void Main(string[] args)        {            Expression<del> myET = x => x * x;            Console.WriteLine(myET);//得到x => ( x * x )             Console.Read();        }    }    delegate int del(int i);    class Program    {        static void Main(string[] args)        {            del myET = new del((x, y) => x + y);             Console.WriteLine(myET(7,8));//15             Console.Read();        }    }    delegate int del(int i,int y); 1.2 带有标准查询运算符的 Lambda许多标准查询运算符都具有输入参数，其类型是泛型委托的 Func<T, TResult> 系列的其中之一。 Func<T, TResult> 委托使用类型参数定义输入参数的数目和类型，以及委托的返回类型。            Func<int, bool> myFunc = x => x == 5;            bool result = myFunc(6); //得到false            Console.WriteLine(result);            int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };            int oddNumbers = numbers.Count(n => n % 2 == 1);//得到5(除2取余等于1的数字个数)            Console.WriteLine(oddNumbers);1.3 Lambda 表达式创建表达式树在将 lambda 表达式分配给 Expression<TDelegate> 类型的变量时，编译器将发出代码以生成一个表示 lambda 表达式的表达式树。             Expression<Func<int, bool>> lambda = num => num < 5;            Console.WriteLine(lambda);//得到num =>( num < 5 ) 1.4 API 创建表达式树            ParameterExpression numParam = Expression.Parameter(typeof(int), "num");            ConstantExpression five = Expression.Constant(5, typeof(int));            BinaryExpression numLessThanFive = Expression.LessThan(numParam, five);            Expression<Func<int, bool>> lambda1 =                Expression.Lambda<Func<int, bool>>(                    numLessThanFive,                    new ParameterExpression[] { numParam });             Console.WriteLine(numParam);//得到num            Console.WriteLine(five);//5            Console.WriteLine(numLessThanFive);//得到( num < 5 ) 1.5 分析表达式树            Expression<Func<int, bool>> exprTree = num => num < 5;             ParameterExpression param = (ParameterExpression)exprTree.Parameters[0];            BinaryExpression operation = (BinaryExpression)exprTree.Body;            ParameterExpression left = (ParameterExpression)operation.Left;            ConstantExpression right = (ConstantExpression)operation.Right;             Console.WriteLine("Decomposed expression: {0} => {1} {2} {3}",                              param.Name, left.Name, operation.NodeType, right.Value);//得到Decomposed expression:num => num LessThan 5 1.6 编译表达式树            Expression<Func<int, bool>> expr = num => num < 5;            Func<int, bool> result = expr.Compile();             Console.WriteLine(result(4));//True            Console.WriteLine(expr.Compile()(5));//False1.7 执行表达式            BinaryExpression be = Expression.Power(Expression.Constant(2D), Expression.Constant(3D));            Expression<Func<double>> le = Expression.Lambda<Func<double>>(be);            Func<double> compiledExpression = le.Compile();            double result = compiledExpression();            Console.WriteLine(result);//得到8