组播代理必须具有void的返回类型。为什么？ [英] Multicast Delegates must have a return type of void. Why?

问题描述

组播代理必须有一个返回类型为void否则将抛出异常。

我想知道背后的原因是什么，如果多个方法可以与代理人相同的返回类型？

解决方案

前提是错误的;它工作正常：

  Func< int> func = delegate {Console.WriteLine（first part）;返回5; }; 
 func + = delegate {Console.WriteLine（second part）;返回7; }; 
 int result = func（）; 
  

这是一个具有非void结果的多播委托，工作正常。您可以从控制台看到两个部分都执行。最后一个项目的结果是返回的结果。我们可以证明这是一个真正的多播委托：

  if（func是MulticastDelegate）Console.WriteLine（我是多播）; 
  

即使在第一行之后，它也会写我是多播 em>（当只列出一种方法时）

如果您需要对单个结果的更多控制，请使用 GetInvocationList（）：

  foreach（Func< int> part in func.GetInvocationList（））
 {
 int result = part（）; 
} 
  

可让您查看每个单独的结果。

在IL术语中：

  .class public auto ansi sealed Func< + TResult> 
扩展System.MulticastDelegate` 
  

这就是说： Func< ; T> 继承自 MulticastDelegate 。基本上，对于所有意图和目的，.NET中的所有代表都是多播代理。您可以可以在托管C ++中获取非多播委托，我不知道。但肯定不是从C＃。

Multicast Delegates must have a return type of void Otherwise it will throw an exception.

I want to know whats the reason behind it, what if multiple methods could have a same return type as of a delegate ?

解决方案

The premise is wrong; it works fine:

Func<int> func = delegate { Console.WriteLine("first part"); return 5; };
func += delegate { Console.WriteLine("second part"); return 7; };
int result = func();

That is a multicast delegate with a non-void result, working fine. You can see from the console that both parts executed. The result of the last item is the one returned. We can demonstrate that this is a true multicast delegate:

if(func is MulticastDelegate) Console.WriteLine("I'm multicast");

and it will write "I'm multicast" even after just the first line (when there is only a single method listed).

If you need more control over individual results, then use GetInvocationList():

foreach (Func<int> part in func.GetInvocationList())
{
    int result = part();
}

which allows you to see each individual result.

In IL terminology:

.class public auto ansi sealed Func<+ TResult>
    extends System.MulticastDelegate`

which is to say: Func<T> inherits from MulticastDelegate. Basically, to all intents and purposes, all delegates in .NET are multicast delegates. You might be able to get a non-multicast delegate in managed C++, I don't know. But certainly not from C#.

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