Question

I’m new to writing singletons and I have to use one for a current iOS project. One of the requirements is that it can be killed. I know this goes against the design of a singleton, but is this something that should/could be done?

Answer 1

Of course it could be done, but if you’re looking for an object that can be created, and then released when not needed… that sounds like a regular object. 🙂

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Generally singletons control their own lifecycles. You’re going to get one-sided discussion here unless you say more about the two requirements (one, that you use a singleton, and two, that it can be released at will), and why they both make sense in your case.

It might be because the singleton wraps some other resource that is inherently unique (like a file resource or network connection). If this is true, then generally the singleton is the “manager” of that resource, and you’d expose control of that resource via the singleton’s interface.

Or it might be because the singleton object holds on to a ton of memory (a buffer of some sort), and you want to be sure that’s flushed as necessary. If this is the case, then you can be smarter about each of its methods creating and releasing memory as necessary, or you can have the singleton listen for the low memory system notifications and behave appropriately.

Essentially, I’d be hard pressed to construct a case where it really made sense for the singleton object itself to be released. A single basic object takes only a handful of bytes in memory, and hurts no one by hanging around.