using null-coalescing operator inside if statement (C#)

Question

I know null-coalescing operator returns the left hand operand if it is not null, but I hadn't seen anyone using it in an if-statement like:

if (car.IsSold ?? false)
 ...

I'm guessing it means if car.IsSold is not null then proceed with the if statement, otherwise jump out of the statement. Is that right? if yes, why shouldn't the programmer use

if (car.IsSold)
...

which does the exact same thing? I'd appreciate if someone clears this up for me.

Comments are not for extended discussion; this conversation has been moved to chat. — Cody Gray
– Cody Gray ♦, Commented Jan 6, 2023 at 11:13

David · Accepted Answer · 2018-10-08 17:18:49Z

2

which does the exact same thing?

No it doesn't. Because a bool? (or Nullable<bool>) and a bool are not the exact same thing.

An if condition must resolve to a bool. But a bool? might resolve to null at runtime. So the compiler won't allow that. You have to provide logic in the condition which will still return a bool in the event that the value in question is null. Probably the simplest way to do that is the null-coalescing operator and a default literal.

answered Oct 8, 2018 at 17:18

David

221k42 gold badges245 silver badges337 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

adjan Over a year ago

the reason the compiler does not allow that isn't bc it might resolve to null.. it's bc that there is no implicit cast

David Over a year ago

@Adrian: Two ways of saying the same thing, really. The compiler is attempting to interpret the condition as a bool because that's what it requires. If the result is a bool, the necessity is met. If it isn't, the compiler attempts to find an implicit cast from whatever the condition does resolve to. Ultimately it needs to become a bool.

adjan Over a year ago

no, you're arguing that it won't allow that bc it might resolve to null. If you explicitly cast to bool it still might, but it will compile

David Over a year ago

@Adrian: Which would result in a runtime error instead of a compile time error, which the compiler is specifically meant to avoid. But still it's semantically the same thing that I've described. The explicit cast resolves to a bool (at least as far as the compiler is concerned, since it's really the developer telling the compiler "don't worry about this, I promise it'll be a bool"), which is what an if requires. The explicit cast may fail at runtime, but that's a different problem. We're both saying the same thing, and we're both right, we're just describing it differently to the OP.

adjan · Accepted Answer · 2018-10-08 17:30:28Z

2

Assuming car.IsSold is nullable:

if (car.IsSold)

does not even compile since bool? does not implicitly cast to bool

The explicit cast

 if ((bool)car.IsSold)

will throw an exception if car.IsSold is null

Using the null-coalescing operator

if (car.IsSold ?? false)

would work in this case, among other solutions.

edited Oct 8, 2018 at 17:30

answered Oct 8, 2018 at 17:17

adjan

13.7k2 gold badges35 silver badges53 bronze badges

4 Comments

Sebastian Hofmann Over a year ago

Or simply use car.IsSold.GetValueOrDefault() which returns false if IsSold is null.

da_berni Over a year ago

@SebastianHofmann In this case I find the null-coalescing operator way more readable, but that's just a personal preference.

pm100 Over a year ago

@SebastianHofmann actually i think the ?? version is better, its less typing and the default is explicitly given

Sebastian Hofmann Over a year ago

@da_berni yeah, I'd also prefer the ?? operator, I was just adding an option.

Collectives™ on Stack Overflow

using null-coalescing operator inside if statement (C#)

2 Answers 2

4 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related