using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Linq.Expressions;

namespace 阐述lambda

{

    class Program

    {

        delegate int GuangChaoshi(int a);

        /// <summary>

        /// 委托  逛超市

        /// </summary>

        /// <param name="a">花费</param>

        /// <param name="b">付钱</param>

        /// <returns>找零</returns>

        delegate int GuangChaoshi2(int a, int b);

        //结账

        public static int JieZhang(int a)

        {

            return a + ;

        }

        public class Person

        {

            public string Name { get; set; }

            public int Age { get; set; }

        }

        public static List<Person> PersonsList()

        {

            List<Person> persons = new List<Person>();

            for (int i = ; i < ; i++)

            {

                Person p = new Person() { Name = i + "儿子", Age =  - i, };

                persons.Add(p);

            }

            return persons;

        }

        static void Main(string[] args)

        {

            List<Person> persons = PersonsList();

            persons = persons.Where(p => p.Age > ).ToList();       //所有Age>6的Person的集合

            Person per = persons.SingleOrDefault(p => p.Age == );  //Age=1的单个people类

            persons = persons.Where(p => p.Name.Contains("儿子")).ToList();   //所有Name包含儿子的Person的集合

            //

            GuangChaoshi gwl = JieZhang;

            Console.WriteLine(gwl() + "");   //打印20，委托的应用

            Console.ReadKey();

            //

            GuangChaoshi gw2 = p => p + ;

            Console.WriteLine(gw2() + "");   //打印20，表达式的应用

            Console.ReadKey();

            //

            GuangChaoshi2 gw3 = (p, z) =>

            {

                int zuidixiaofei = ;

                if (p < zuidixiaofei)

                {

                    return ;

                }

                else

                {

                    return z - p - ;

                }

            };

            Console.WriteLine(gw3(, ) + "");   //打印80，z对应参数b，p对应参数a

            Console.ReadKey();

            //4

            //i*j+w*x

            ParameterExpression a = Expression.Parameter(typeof(int), "i");   //创建一个表达式树中的参数，作为一个节点，这里是最下层的节点

            ParameterExpression b = Expression.Parameter(typeof(int), "j");

            BinaryExpression be = Expression.Multiply(a, b);    //这里i*j,生成表达式树中的一个节点，比上面节点高一级

            ParameterExpression c = Expression.Parameter(typeof(int), "w");

            ParameterExpression d = Expression.Parameter(typeof(int), "x");

            BinaryExpression be1 = Expression.Multiply(c, d);

            BinaryExpression su = Expression.Add(be, be1);   //运算两个中级节点，产生终结点

            Expression<Func<int, int, int, int, int>> lambda = Expression.Lambda<Func<int, int, int, int, int>>(su, a, b, c, d);

            Console.WriteLine(lambda + "");   //打印‘(i,j,w,x)=>((i*j)+(w*x))’，z对应参数b，p对应参数a

            Func<int, int, int, int, int> f = lambda.Compile();  //将表达式树描述的lambda表达式，编译为可执行代码，并生成该lambda表达式的委托；

            Console.WriteLine(f(, , , ) + "");  //打印2

            Console.ReadKey();

            //

            Func<int, string> gw5 = p => p +  + "--返回类型为string";

            Console.WriteLine(gw5() + "");   //打印‘20--返回类型为string’，z对应参数b，p对应参数a

            Console.ReadKey();

            //

            Func<int, int, bool> gw6 = (p, j) =>

            {

                if (p + j == )

                {

                    return true;

                }

                return false;

            };

            Console.WriteLine(gw6(, ) + "");   //打印‘True’，z对应参数b，p对应参数a

            Console.ReadKey();

        }

    }

}