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        Func Delegate vs Function(函数委托与函数)
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                • 本文介绍了函数委托与函数的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!


                  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 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"));
                      // 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);




                  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?


                  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. 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 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. When you do:

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

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

                  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.




                  Multicast delegate weird behavior in C#?(C# 中的多播委托奇怪行为?)
                  Parameter count mismatch with Invoke?(参数计数与调用不匹配?)
                  How to store delegates in a List(如何将代表存储在列表中)
                  How delegates work (in the background)?(代表如何工作(在后台)?)
                  C# Asynchronous call without EndInvoke?(没有 EndInvoke 的 C# 异步调用?)
                  Delegate.CreateDelegate() and generics: Error binding to target method(Delegate.CreateDelegate() 和泛型:错误绑定到目标方法)

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