Who's Afraid of the big-bad cast operator?

re: Who's Afraid of the big-bad cast operator?

Mike — Mon, 24 Mar 2008 20:13:13 GMT

Just a couple of days ago I saw "as" being used 4 times in 2 lines of code! Sheesh, especially that those 4 casts could have been reduced to just 2 but that's another story.

As for why people use "as" instead of "is" you may be right that they are sort of afraid of cast exceptions but when I see "as" being used without a subsequent null check I tend to believed that they simply started writing code, realised that they need to cast something to get what they need and just slapped an "as" in.

re: Who's Afraid of the big-bad cast operator?

Jeff Yates — Tue, 25 Mar 2008 21:24:03 GMT

Thanks for blogging this. It's been a battle on our project to highlight when and when not to use "as" and regular casts. You've put it succinctly, although i think "is" requires mention.

In my opinion, an "as" should be used if the code uses "is" followed by a cast if the "is" returns true, as the "as" does both these actions. If the value must ALWAYS be the type, a regular cast should be used; if the value doesn't matter and only the type does, the "is" should be used.

Like I said, thanks. :)

re: Who's Afraid of the big-bad cast operator?

Raj — Tue, 25 Mar 2008 22:57:14 GMT

We use the following pattern a lot in our asp.net applications:

Button btn = foo.FindControl("Button") as Button;

if (btn != null) {

btn.Visible = false;

}

.. in places where the button is not guaranteed to exist.

re: Who's Afraid of the big-bad cast operator?

Shahar — Tue, 25 Mar 2008 23:02:23 GMT

If a button is not guaranteed to exist or if .FindControl("button") may return a different class than Button, then this is, in mind, a great way of using "as".

If, on the other hand, your application is guaranteed to always have a button under that name (which it doesn't), a cast is probably better.

re: Who's Afraid of the big-bad cast operator?

thelever — Wed, 26 Mar 2008 11:14:33 GMT

If you embark on a voyage that will have you do both "is" and "as", you are most likely wasting time as "is" is basically "as" with a check for null. You are now doing that twice.