理解Lambda表达式和闭包

了解由函数指针到Lambda表达式的演化过程

Lambda表达式的这种简洁的语法并不是什么古老的秘法,因为它并不难以理解(难以理解的代码只有一个目的,那就是吓唬程序员)

 #include "stdafx.h"
 using namespace System;

 typedef void(*FunctionPointer)(System::String ^str);

 void HelloWorld(System::String ^str)
 {
     Console::WriteLine(str);
     Console::ReadLine();
 }

 int main(array<System::String ^> ^args)
 {
     FunctionPointer fp = HelloWorld;
     fp("Hello World");
     return ;
 }

函数指针

 using System;
 using System.Collections.Generic;
 using System.Text;

 namespace CharpFunctionPointer {
     class Program {

         delegate void FunctionPointer(string str);

         static void Main(string[] args) {
             FunctionPointer fp = HelloWorld;
             fp("Hello World!");
         }

         static void HelloWorld(string str) {
             Console.WriteLine(str);
             Console.ReadLine();
         }
     }

 }

委托

 using System;
 using System.Collections.Generic;
 using System.Text;

 namespace CharpFunctionPointer {
     class Program {

         delegate void FunctionPointer(string str);

         static void Main(string[] args) {
             FunctionPointer fp = delegate (string s) {
                 Console.WriteLine(s);
                 Console.ReadLine();
             };
             fp("Hello World!");
         }
     }

 }

匿名委托

 using System;
 using System.Collections.Generic;
 using System.Text;

 namespace CharpFunctionPointer {
     class Program {

         delegate void FunctionPointer(string str);

         static void Main(string[] args) {
             FunctionPointer fp =
                 s => Console.WriteLine(s);

             fp("Hello World!");
             Console.ReadLine();
         }
     }
 }

Lambda表达式

 using System;
 using System.Collections.Generic;
 using System.Text;

 namespace CharpFunctionPointer {
     class Program {

         static void Main(string[] args) {
             Action<string> fp = s => Console.WriteLine(s);

             fp("Hello World!");
             Console.ReadLine();
         }
     }
 }

将Lambda表达式赋值给一个预定义的泛型委托

Lambda表达式和闭包

 using System;
 using System.Collections.Generic;
 using System.Text;
 using System.Linq;

 namespace LambdaClosure {
     class Program {

         static void Main(string[] args) {
             UsesClosure();
         }

         static void UsesClosure() {
             string toFind = "ed";
             var words = new string[] {
                 "ended","friend","closed","potato"
             };

             var matches = words.Select(s => s.Contains(toFind));
             foreach(var str in matches) {
                 Console.WriteLine(str);
             }
             Console.ReadLine();
         }
     }
 }

使用本地变量toFind就会通知编译器生成一个闭包(或包装器类),这样,toFind就不会成为"未定义"

柯里化(Currying)

 using System;
 using System.Collections.Generic;
 using System.Text;
 using System.Linq;

 namespace LambdaCurry {
     class Program {

         static void Main(string[] args) {
             Func<int,int,int> longLambda = (x,y) => x + y;
             Console.WriteLine(longLambda(,));

             //currying
             Func<int,Func<int,int>> curry = x => y => x + y;
             Console.WriteLine(curry()());

             Console.ReadLine();
         }
     }
 }

LambdaCurry