在if语句（C＃）中使用空合并运算符

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.

Answer 1

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.

Answer 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.