学习lamda表达式

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 + 10;
}

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 = 0; i < 7; i++)
{
Person p = new Person() { Name = i + "儿子", Age = 8 - i, };
persons.Add(p);
}
return persons;
}

static void Main(string[] args)
{
List<Person> persons = PersonsList();
persons = persons.Where(p => p.Age > 6).ToList();       //所有Age>6的Person的集合
Person per = persons.SingleOrDefault(p => p.Age == 1);  //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
//1
GuangChaoshi gwl = JieZhang;
Console.WriteLine(gwl(10) + "");   //打印20，委托的应用
Console.ReadKey();
//2
GuangChaoshi gw2 = p => p + 10;
Console.WriteLine(gw2(10) + "");   //打印20，表达式的应用
Console.ReadKey();

//3
GuangChaoshi2 gw3 = (p, z) =>
{
int zuidixiaofei = 10;
if (p < zuidixiaofei)
{
return 100;
}
else
{
return z - p - 10;
}

};
Console.WriteLine(gw3(10, 100) + "");   //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(1, 1, 1, 1) + "");  //打印2
Console.ReadKey();

//5
Func<int, string> gw5 = p => p + 10 + "--返回类型为string";
Console.WriteLine(gw5(10) + "");   //打印‘20--返回类型为string’，z对应参数b，p对应参数a
Console.ReadKey();
//6
Func<int, int, bool> gw6 = (p, j) =>
{
if (p + j == 10)
{
return true;
}
return false;
};
Console.WriteLine(gw6(5, 5) + "");   //打印‘True’，z对应参数b，p对应参数a
Console.ReadKey();
}

}
}