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Consider the following: I have controllers and views in a client-application. As this runs purely on the client side, each controller must only exist once.

At first I thought about implementing everything as Singletons but this doesn't really feel right for a few reasons.

A few is instantiated like so: 

abstract class View(controller: Controller)

now in each view I do certain things, based on the controller I got.

Some controllers need to have parameters set upon initialization, this speaks for a class, rather than a singleton. (Of course I could do: MyObject.set(whatever) but that's neither clean nor nice)

Now my idea was to create a simple mutable HashMap for the controllers and store the classes as keys and exactly one corresponding object as a value.

Now upon each initialization I just check the HashMap for an instance and if there is one already, I return that instead.

Seems hacky though.

Of course I could just stick with classes all the way, but I'm not sure if this is a good way. I mean, if I instantiate new Controllers every few seconds ... (It's a game we're talking about, so there is already a lot of calculations going on)

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  • You have an unusual interpretation of Controllers and Views. If you followed the MVC pattern you wouldn't have this issue because a View is decided by the Controller and always receives the same Model definition. I'm not saying that you're wrong because I don't know your problem. However I thought it worth pointing this out in case it helps
    – Brad
    Jul 18, 2015 at 17:08
  • I'm not using MVC per se. I'm using my own MVC "light" for a game. There a controller has a view and if you click a button in a few, you call a controller method. Some of these methods create new instances of other controllers to delegate the logic there. Like for example: goToMainMenu() called in a SubMenu would activate the MainMenuController and init its view. A View here does not get any model, well, the "models" here are just Singleton-Loaders and some wrapper-classes that load/parse some data to be represented :) Now I don't want to create new Controllers each time I hit"back" and "forth
    – Sorona
    Jul 18, 2015 at 17:17

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At a high level, you're essentially asking:

Is building a Controller cache better than using singletons?

I would argue that in your situation, yes, it is. And here's why.

From your description it doesn't sound like you need the semantics of a singleton here. Your game would be just fine if you instantiated a new Controller every time one was needed.

In other words, your requirement isn't: All references to a Controller must resolve to a single unique Controller state."

Instead, your requirement seems to be: When retrieving a Controller instance, it should be fast.

That is an argument for using a cache. Not singletons.

If you want to implement that cache using a HashMap then go for it :)

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  • Thanks! What other options, apart from a HashMap do you see? Class as key is fine? Or would String-comparison be faster?
    – Sorona
    Jul 18, 2015 at 11:48
  • I haven't built a cache (or focused on performance for that matter) in years, so I wouldn't be able to tell you. sorry!
    – MetaFight
    Jul 18, 2015 at 11:51
  • For very small datasets, iterating an ArrayList can be faster than looking up in a HashMap. I am not sure though where the limit was. I think I read it somewhere on Stackoverflow, but I can't find the question right now.
    – Philipp
    Jul 18, 2015 at 12:25
  • @Teolha I don't know which language you are working in, but if you can get a class pointer in your language, that's likely faster than using a string as a key. Hashing a string generally has to work character by character, hashing a pointer can work on larger chunks. Nevertheless, it really depends on the hash function: a bad hash function will produce a lot of unnecessary collisions given pointers, which will slow things down. So it's the old optimization mantra: Truth is only in measurement.
    – cmaster - reinstate monica
    Jul 18, 2015 at 12:25

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