When I was learning to code, I read up on the design patterns like a good boy. Long after this, I started to actually understand them.

Design discussions such as those on this site constantly try to make the rules more and more general, which is good. But there is a line, over which it becomes over-analysis starts to feed off itself and as such I think begins to obfuscate the original point - for example the "What's Alternative to Singleton" post and the links contained therein.

http://stackoverflow.com/questions/1300655/whats-alternative-to-singleton

I say this having been asked in both interviews I’ve had over the last 2 weeks what a singleton is and what criticisms I have of it.

I have used it a few times for items such as user data (simple key-value eg. last file opened by this user) and logging (very common i'm sure). I've never ever used it just to have what is essentially global application data, as this is clearly stupid.

In the first interview, I reply that I have no criticisms of it. He seemed disappointed by this but as the job wasn’t really for me, I forgot about it.

In the next one, I was asked again and, as I wanted this job, I thought about it on the spot and made some objections, similar to those contained in the post linked to above (I suggested use of a factory or dependency injection instead). He seemed happy with this.

But my problem is that I have used the singleton without ever using it in this kind of stupid way, which I had to describe on the spot. Using it for global data and the like isn’t something I did then realised was stupid, or read was stupid so didn’t do, it was just something I knew was stupid from the start. Essentially I’m supposed to be able to think of ways of how to misuse a pattern in the interview? Which class of programmers can best answer this question? The best ones? The medium ones? I'm not sure....

And these were both bright guys. I read more than enough to get better at my job but had never actually bothered to seek out criticisms of the most simple of the design patterns like this one.

Do people think such questions are valid and that I ought to know the objections off by heart? Or that it is reasonable to be able to work out what other people who are missing the point would do on the fly? Or do you think I’m at least partially right that the question is too unsubtle and that the questions ought to be better thought out in order to make sure only good candidates can answer.

PS. Please don’t think I’m saying that I’m just so clever that I know everything automatically - I’ve learnt the hard way like everyone else. But avoiding global data is hardly revolutionary.