The question mark makes it nullable

As others said, it means nullable, but to put it in more intuitive, less-jargony way - it's a question mark bc you don't know if the value is actually there or not. It could be a Singleton, but it isn't until you check if there is a value. Whereas if you have, idk, int a no question mark, then you're saying you actually have data.

Essentially with C# 8, they "removed" null and reused the idea of null references in creating what is essentially an Option like in other languages. You either have some data of some type, or none (a null reference, in this case). By default, everything has to be there. Then when you need null, e.g. you may not have something initialized or an operation could fail, you explicitly grab for it. Thus it reduces null pointer bugs. If you don't need nullability, you can ensure that you don't accidentally write in an issue. It safety checks statements and parameters.

I agree that the more verbose style is more explicit, and so more readable.

On its face, its readable. But when you're dealing with 10,000 lines of code in a file, it becomes this ugly morass of extra nothingness to scroll through.

The only part that has me stumped is the unary question-mark operator: private static Singleton? _instance = null;

It transforms a strict variable into a nullable variable. I most commonly see it with primitive types.

So, for instance

int myInt = null

is an illegal assignment, but

int? myInt = null

works fine.

Why does a public class instantiation need this? Idfk. That might be extraneous. But I wouldn't throw away the whole code block rewrite over that one character.

I can figure most of the new style out from context.

• => is clearly a closure declaration operator, similar to JavaScript.
• x ??= y is shorthand for "assign y to x if x is not set, and return x" which is kind of nice.

Man, I've successfully stayed away from C# for a few years now, but that's wild to me that the x ??= y operator would be intuitive to you.
This could've easily been two or three operations, without being much more verbose, but actually being somewhat intuitively readable for most devs...

Nullable: Type? means Type or null

The only thing that's not obvious to me is that ??= doesn't seem to invoke new Singleton() if it's already defined, essentially short-circuiting. Otherwise I would have to look up the semantics of it if I were worried about that constructor having side effects or doing something heavy.