Func代表vs功能 [英] Func Delegate vs Function

问题描述

有人可以告诉我使用代理的优点，而不是如下所示调用函数本身（或者换句话说，为什么选择选项A超过选项B）？昨天晚上我正在看一个人的linq代码，他们有一个类似于Option A的东西，但它被用来返回一个编译的linq查询。

我意识到前者现在可以被传递到其他功能..只是不确定其实用性。 BTW，我意识到这将不会按原样编译..在发布之前未注释的功能之一。 TYIA

  class Program 
 {
 static void Main（string [] args）
 { 
 Console.WriteLine（SayTwoWords（Hello，World））; 
 Console.ReadKey（）; 
} 
 
 //选项A 
 private static Func< string，string，string> 
 SayTwoWords =（a，b）=> String.Format（{0} {1}，a，b）; 
 
 //选项B 
私有静态字符串SayTwoWords（string a，string b）
 {
 return String.Format（{0} {1}， a，b）; 
} 
} 
  

*********** *编辑************

不知道如果它更好地解释了我的问题，但这里是一个原始类型的代码的例子我想到这一点：

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

以这种方式编写函数有什么好处吗？

解决方案

您发布的代码没有任何优势。在您的代码中，使用代理只会增加复杂性以及额外的运行时费用，所以您最好直接调用方法。

但是，代理有很多用途。 传递到其他方法是主要的用法，虽然存储函数和使用它以后也是非常有用的。

LINQ完全基于这个概念。当你这样做：

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

您正在传递一个委托（定义为lambda： item => ; item ==Foo）到LINQ库中的其中函数。这是什么使它正常工作。

Can someone tell me the advantages of using a 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 A but it was being used to return a compiled linq query.

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

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

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

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

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

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

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

Is there any advantage to writing a function in this way?

解决方案

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

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

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

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

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

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