Question

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

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

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?

Answer 1

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.

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(); });