什么是扩展方法？ [英] What are Extension Methods?

问题描述

什么是.NET扩展方法？

编辑： 我已经发布的后续问题，在扩展方法 用法

解决方案

  

扩展方法允许开发者添加新的方法向公众   现有的CLR类型的合同，   而无需子类，或   重新编译原来的类型。

     

扩展方法帮助交融   的鸭打字支持的灵活性   动态语言在当今流行   与性能和编译时   强类型的验证   语言。

参考：<一href="http://weblogs.asp.net/scottgu/archive/2007/03/13/new-orcas-language-feature-extension-methods.aspx" rel="nofollow">http://weblogs.asp.net/scottgu/archive/2007/03/13/new-orcas-language-feature-extension-methods.aspx

下面是一个扩展方法的样本（注意这关键字盈方的第一个参数）：

 公共静态布尔IsValidEmailAddress（这个字符串s）
{
    正则表达式的regex ​​=新的正则表达式（@^ [\ W  -​​  \。] + @（[\ w  - ] + \）+ [\ w  - ] {2,4} $）;
    返回regex.IsMatch（多个）;
}
 

现在，上面的方法，可直接从任何字符串调用，像这样的：

  BOOL的isValid =[e-mail]（）;
 

然后添加的方法也将出现在智能感知：

至于实际使用的扩展方法，你可以添加新的方法到类没有派生新类。

看看下面的例子：

 公共类扩展{
    公众诠释总和（）{
        返回7 + 3 + 2;
    }
}

公共静态类扩展{
    公共静态持股量平均（这个扩展extnd）{
        返回extnd.Sum（）/ 3;
    }
}
 

正如你所见，类扩展是加入了一个名为方法平均上课扩展。为了获得平均，你叫平均的方法，因为它属于扩展类：

 扩展EX =新的扩展（）;

Console.WriteLine（ex.average（））;
 

参考：<一href="http://aspguy.word$p$pss.com/2008/07/03/a-practical-use-of-serialization-and-extension-methods-in-c-30/" rel="nofollow">http://aspguy.word$p$pss.com/2008/07/03/a-practical-use-of-serialization-and-extension-methods-in-c-30/

What are extension methods in .NET?

EDIT: I have posted a follow up question at Usage of Extension Methods

解决方案

Extension methods allow developers to add new methods to the public contract of an existing CLR type, without having to sub-class it or recompile the original type.

Extension Methods help blend the flexibility of "duck typing" support popular within dynamic languages today with the performance and compile-time validation of strongly-typed languages.

Reference: http://weblogs.asp.net/scottgu/archive/2007/03/13/new-orcas-language-feature-extension-methods.aspx

Here is a sample of an Extension Method (notice the this keyword infront of the first parameter):

public static bool IsValidEmailAddress(this string s)
{
    Regex regex = new Regex(@"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$");
    return regex.IsMatch(s);
}

Now, the above method can be called directly from any string, like such:

bool isValid = "[e-mail]".IsValidEmailAddress();

The added methods will then also appear in IntelliSense:

As regards a practical use for Extension Methods, you might add new methods to a class without deriving a new class.

Take a look at the following example:

public class Extended {
    public int Sum() {
        return 7+3+2;
    }
}

public static class Extending {
    public static float Average(this Extended extnd) {
        return extnd.Sum() / 3;
    }
}

As you see, the class Extending is adding a method named average to class Extended. To get the average, you call average method, as it belongs to extended class:

Extended ex = new Extended();

Console.WriteLine(ex.average());

Reference: http://aspguy.wordpress.com/2008/07/03/a-practical-use-of-serialization-and-extension-methods-in-c-30/

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