[zaphar]

Over reliance on singletons can indeed be less maintainable, less testable, and less flexible than dependency injection.

However sometimes a singleton is in fact more maintainable and improves the code massively. Nor do they have to be less testable when implemented well.

None of which detracts from the article which is about consistency in the code base. A knew jerk reaction to the singleton completely misses the point.

[thedudemabry]

I totally agree that the singleton detail is beside the article's point, but what is the modern case for singletons? It seems like singletons are now considered a synonym for global variables. What other purpose do they serve?

[zaphar]

I wrote a singleton just the other day. I dont often write these but occasionally they are useful.

It enabled us to decouple some code deep down in our architecture and enforce some constraints around the use of this particular piece.

When you actually need a singleton it's best to use one and call it out as such so people know what they are dealing with. Dependency injection will often be passing around a singleton everywhere without people being aware that it's a singleton and all that that means.

[jeremiep]

I've never seen a singleton I couldn't refactor away. Removing singletons always makes dependencies between modules more explicit which is a good thing.

[Retra]

I wrote a singleton the other day. Using Java, I had a static utility class that had a function that I wanted to memoize. So I put a static HashMap in the class to do the lookups. There's no reason to have multiple copies, and it's easy to instantiate it only if it is needed.

[thedudemabry]

That's reasonable, but it seems to be equivalent to creating a top-level function and associated global variable in other languages. Java's prohibition of those constructs necessitated the class wrapper, but doesn't appear to provide any benefits over another more generalizable method, namespacing.

[Retra]

That's true. If I weren't using java, I wouldn't have had to use a singleton. That's as much of a problem with singletons as it is an over-reliance on the object-oriented style.

I suspect dependency injection has the same problem: you could achieve the same results in a non-object-oriented language.