C#知识：匿名方法、Lambda表达式与闭包

闭包乍一听感觉很复杂，其实一点也不简单

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1、匿名方法

• 没有方法名的方法
• 一般用于委托和事件

Func<int, int, int> myAction  = delegate(int a, int b) { return a + b; };
Console.WriteLine( myAction(1, 2)); //3

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2、Lambda表达式

• 作用类似匿名函数
• 可以省略参数类型，大括号和return关键字

myAction = (a, b) => a * b;
Console.WriteLine(myAction(2,3));   //6

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3、闭包

• 是内层函数与引用的外层函数中的外部变量的绑定
• 闭包会延长所引用的外部变量的生命周期
• 从绑定关系角度来看，闭包中的外部变量对于内层函数，类似于静态成员变量对于类变量

static void Test(ref Func<int> myFunc)
{
    int value = 2;
    myFunc = () => ++value;
}

Func<int> myFunc = null;
Test(ref myFunc);
Console.WriteLine(myFunc());    //3
Console.WriteLine(myFunc());    //4

• 内层函数会捕获外部变量的引用

这里闭包中捕获的是myCake对象的引用，在外面修改了myCake对象的成员变量的值，修改也会反映到闭包中。

static Cake Test2(ref Func<int> myFunc) 
{
    Cake myCake = new Cake(100);
    myFunc = () => ++myCake.price;
    myCake.price += 10;
    return myCake;
}

Func<int> myFunc2 = null;
Cake fruitCake = Test2(ref myFunc2);
Console.WriteLine(myFunc2());   //111
Console.WriteLine(myFunc2());   //112
fruitCake.price = 10086;
Console.WriteLine(myFunc2());   //10087
Console.WriteLine(myFunc2());   //10088

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4、完整代码示例

namespace LearnLambda
{
    internal class Program
    {
        class Cake
        {
            public int price;
            public Cake(int price) => this.price = price;
        }
        static void Test(ref Func<int> myFunc)
        {
            int value = 2;
            myFunc = () => ++value;
        }
        static Cake Test2(ref Func<int> myFunc) 
        {
            Cake myCake = new Cake(100);
            myFunc = () => ++myCake.price;
            myCake.price += 10;
            return myCake;
        }
        static void Main(string[] args)
        {
            //匿名方法
            Func<int, int, int> myAction  = delegate(int a, int b) { return a + b; };
            Console.WriteLine( myAction(1, 2)); //3
            //Lambda表达式
            myAction = (a, b) => a * b;
            Console.WriteLine(myAction(2,3));   //6
            //闭包
            Func<int> myFunc = null;
            Test(ref myFunc);
            Console.WriteLine(myFunc());    //3
            Console.WriteLine(myFunc());    //4

            Func<int> myFunc2 = null;
            Cake fruitCake = Test2(ref myFunc2);
            Console.WriteLine(myFunc2());   //111
            Console.WriteLine(myFunc2());   //112
            fruitCake.price = 10086;
            Console.WriteLine(myFunc2());   //10087
            Console.WriteLine(myFunc2());   //10088
        }
    }
}

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5、参考资料

1. 《唐老狮C#》
2. C#—闭包详解

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本篇结束，感谢您的阅读~