Is '@' Error Suppression a Valid Technique for Testing for an Optional Array Key?

Question

Rarst and I were debating offline about the use of the '@' error suppression operator in PHP, specifically for use to test for existence of "optional" array keys, i.e. array keys that are being used as a switch here a their lack of existence in the array is functionally equivalent to the array having the key with a value equaling false.

Here is pseudo-code for this scenario:

 function do_something( $args = array() ) {
   if ( @$args['switch'] ) {
      // Do something with this switch
   }
   // continue on...
 }

vs. this approach:

 function do_something( $args = array() ) {
   if ( ! empty( $args['switch'] ) && $args['switch'] ) {
      // Do something with this switch
   }
   // continue on...
 }

Of course in most use-cases, suppressing errors would not be A Good Thing(tm). However in this use-case where an array is passed with an optional element, it seems to me that it is actually a very good technique but I could be wrong and would like to hear other's opinions on the subject before I make up my mind.

I do know that there are alleged performance hits for using the former approach but I'd like to know how they compare with the alternative and if they performance hits really matter in real world scenarios?

P.S. I decided to post this because, after debating this offline with Rarst, he asked a more general question here on Programmers but didn't actually give a detailed example of the specific use-case we were debating. And since I'm pretty sure he'll want to use the out-of-context answers on that other question as justification for why the above is "bad" I decided I needed to get opinions on this specific use-case.

Answer 1

First, when talking about performance penalties, you cannot get a sensible answer unless there is context to where it is to happen.

To illustrate, is a 100ms delay to log a stackdump when a program terminates acceptable? More than likely.

Is that same 100ms delay acceptable in a tight loop that runs each time you process a record from 100 million? Of course not.

Second, how is someone to know you have suppressed the error because you are actually using it for logic-flow control as opposed to not knowing any better and just trying to implement 'See no evil'. Self-documenting code is better than needing explicit comments to assure people of your intentions.

Third, as noted by Yannis in the other question, you are really setting yourself up for failure because of the potential for unintended consequences.

---

So, for the sake of those poor souls that have to maintain your code in the future, just don't do it!

After all, what are you really gaining?