函数委托与函数

问题描述

有人可以告诉我使用委托而不是调用函数本身的优势，如下所示(或者换句话说，为什么选择选项 A 而不是选项 B)?昨晚我在查看某人的 linq 代码，他们有类似于选项 A 的内容，但它被用于返回已编译的 linq 查询.

Can someone tell me the advantages of using a free vpn 免费vpn下载 delegate as opposed to calling the function itself as shown below (or in other words why choose Option A over Option B)? I was looking at someone's linq code last night and they had something similar to Option vpn free A but it was being used to return a compiled vpn下载 免费vpn下载 linq query.

我意识到前者现在可以传递给其他功能......只是不确定它的实用性.顺便说一句，我意识到这不会按原样编译.在发布之前取消注释其中一个功能.TYIA

I realize the former can now be passed free vpn around to other functions.. just not vpn下载 sure of its practicality. BTW, I realize this 免费vpn wouldn't compile as-is.. uncommented one of the functions before posting. TYIA

class Program
{
    static vpn free void Main(string[] args)
  vpn free   { vpn下载   
     免费vpn下载    Console.WriteLine(SayTwoWords("Hello", "World"));
        Console.ReadKey();
    }

    // Option A
    private static Func<string, string, string>
        SayTwoWords = (a, b) => String.Format("{0} {1}", 免费vpn a, b);

  免费vpn   // Option B
    private static string SayTwoWords(string a, string b)
    {
        return String.Format("{0} {1}", a, b);
    } 免费vpn        
}

************编辑************

************EDIT************

不确定它是否更好地解释了我的问题，但这里是最初让我想到这个的代码类型的示例:

Not sure if it explains my question better vpn下载 but here is an example of the type 免费vpn下载 of code that originally got me thinking about this:

public static class clsCompiledQuery
{
 free vpn    public static Func<DataContext, string, IQueryable<clsCustomerEntity>>
        getCustomers = CompiledQuery.Compile((DataContext db, string strCustCode)
    vpn free      免费vpn    => from objCustomer in db.GetTable<clsCustomerEntity>()
            where 免费vpn objCustomer.CustomerCode == strCustCode
            select objCustomer);
}

这样写函数有什么好处吗?

Is there any advantage 免费vpn下载 to writing a function in free vpn this way?

推荐答案

你贴的代码没有优势.在您的代码中，使用委托只会增加复杂性以及额外的运行时成本 - 所以您最好直接调用该方法.

There is no advantage in the code you posted. vpn free In your code, using 免费vpn the delegate just adds complexity as vpn下载 well as an extra vpn下载 runtime cost - so you're better off just calling the method directly.

但是，委托有很多用途.传递"给其他方法是主要用法，但存储一个函数并在以后使用它也非常有用.

However, delegates vpn下载 have many uses. "Passing around" to other methods is the primary usage, though storing a function and using it later 免费vpn is also very useful.

LINQ 完全建立在这个概念之上.当你这样做时:

LINQ is built on top of this concept entirely. vpn下载 When you do:

var results vpn下载 = myCollection.Where(item => item == "Foo");

您将委托(定义为 lambda:item => item == "Foo")传递给 LINQ vpn下载 库中的 Where 函数.这就是让它正常工作的原因.

You're passing a delegate (defined 免费vpn下载 as a 免费vpn lambda: item vpn下载 => item == "Foo") to the Where function in the LINQ libraries. This is what makes it work properly.

这篇关于函数委托与函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！