What is wrong with singleton?
One of the main disadvantages of singletons is that they make unit testing very hard. They introduce global state to the application. The problem is that you cannot completely isolate classes dependent on singletons. When you are trying to test such a class, you inevitably test the Singleton as well.
Are singleton classes bad?
Singleton is not a pattern to wrap globals. Singleton pattern should only be used to guarantee that one and only one instance of a given class exists during run time. People think Singleton is evil because they are using it for globals. It is because of this confusion that Singleton is looked down upon.
Should I use a singleton?
A singleton should be used when managing access to a resource which is shared by the entire application, and it would be destructive to potentially have multiple instances of the same class. Making sure that access to shared resources thread safe is one very good example of where this kind of pattern can be vital.
Why are singletons bad for a design pattern?
The Singleton design pattern is a very specific type of single instance, specifically one that is: Never explicitly freed (implicitly freed on program termination). It is because of this specific design choice that the pattern introduces several potential long-term problems:
What’s the best way to use a singleton?
If you want to take it one step further then you can use an IoC container (DI framework) like Spring (Java) or Unity (.NET). Almost every DI framework will do its own lifetime management and specifically allow you to define a particular service as a single instance (often calling it “singleton”, but that’s only for familiarity).
Why are Gang of Four singleton patterns bad?
The Gang of Four Singleton pattern does two things: give you convenience access to an object from anywhere, and ensure that only one instance of it can be created. 99% of the time, all you care about is the first half of that, and carting along the second half to get it adds unnecessary limitation.
Do you need a singleton for a cache?
If you want to get fancy you can call it an “offline cache” or just an offline copy of remote data. A cache does not need to be a singleton. It may need to be a single instance if you want to avoid fetching the same data for multiple cache instances; but that does not mean you actually have to expose everything to everyone.