using System;

using System.Collections.Generic;

using System.Linq;

​

class LambdaDemo

{

    // 1. 委托类型声明

    delegate int MathOperation(int x, int y);

    static void Main()

    {

        // 2. 基本委托赋值

        MathOperation add = (a, b) => a + b;

        Console.WriteLine($"加法结果：{add(3, 5)}");  // 输出8

​

        // 3. 无参数Lambda

        Action greet = () => Console.WriteLine("\n你好，世界！");

        greet();

​

        // 4. 多参数Lambda

        Func<int, int, string> compare = (x, y) => 

            x > y ? $"{x} 大于 {y}" : $"{x} 不大于 {y}";

        Console.WriteLine(compare(7, 5));  // 输出"7 大于 5"

​

        // 5. 集合操作（LINQ）

        List<int> numbers = new List<int> { 2, 5, 8, 13, 21 };

        var squared = numbers.Select(n => n * n);

        Console.WriteLine("\n平方数：" + string.Join(", ", squared));

​

        // 6. 条件过滤

        var evens = numbers.Where(num => 

        {

            bool isEven = num % 2 == 0;

            return isEven;  // 语句Lambda需要return

        });

        Console.WriteLine("偶数：" + string.Join(", ", evens));

​

        // 7. 事件处理

        var button = new Button();

        button.Click += (sender, e) => 

            Console.WriteLine("\n按钮被点击！时间：" + DateTime.Now);

        button.SimulateClick();

​

        // 8. 异步Lambda

        System.Threading.Tasks.Task.Run(async () => 

        {

            await System.Threading.Tasks.Task.Delay(500);

            Console.WriteLine("\n异步操作完成！");

        });

​

        // 9. 闭包示例

        int factor = 3;

        Func<int, int> multiplier = n => n * factor;

        Console.WriteLine($"\n乘数结果：{multiplier(5)}");  // 输出15

    }

}

​

// 辅助类用于事件示例

class Button

{

    public event EventHandler Click;

    public void SimulateClick()

    {

        Click?.Invoke(this, EventArgs.Empty);

    }

}

​