C＃新[代表]没有必要？ [英] C# new [delegate] not necessary?

问题描述

我一直在玩的HttpWebRequest 取值最近，和教程他们总是这样：

I've been playing with HttpWebRequests lately, and in the tutorials they always do:

IAsyncResult result = request.BeginGetResponse(
  new AsyncCallback(UpdateItem),state);

但新的AsyncCallback 似乎不是necesary。如果的updateItem 具有正确的签名，则似乎没有成为一个问题。那么，为什么人们有吗？是否在所有做什么？

But new AsyncCallback doesn't seem to be necesary. If UpdateItem has the right signature, then there doesn't seem to be a problem. So why do people include it? Does it do anything at all?

推荐答案

这是同样的事情，主要是（也有少数超载规则来想想，虽然未在这个简单的例子）。但在C＃以前的版本中，没有任何委托类型推断。所以这本手册是要么（一）笔试前，委托类型推断可用，或（b），他们希望能详细解释之用。

It's the same thing, mostly (there are a few overload rules to think about, although not in this simple example). But in previous versions of C#, there wasn't any delegate type inference. So the tutorial was either (a) written before delegate type inference was available, or (b) they wanted to be verbose for explanation purposes.

下面是一些摘要方式的不同可以采取委托类型推断的优势：

Here's a summary of a few of the different ways you can take advantage of delegate type inferencing:

// Old-school style.
Chef(new CookingInstructions(MakeThreeCourseMeal));

// Explicitly make an anonymous delegate.
Chef(delegate { MakeThreeCourseMeal });

// Implicitly make an anonymous delegate.
Chef(MakeThreeCourseMeal);

// Lambda.
Chef(() => MakeThreeCourseMeal());

// Lambda with explicit block.
Chef(() => { AssembleIngredients(); MakeThreeCourseMeal(); AnnounceDinnerServed(); });

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