how can I check for the nullability of a variable that should contain a function?

# getting-started

[oday]

how can I check for the nullability of a variable that should contain a function?

[Andreas Sinz]

you mean check if its null and if not call it?

[oday]

yea

[oday]

the declaration itself, where does the ? go?

[oday]

var myFun: () -> Unit? = {}?

[Andreas Sinz]

(() -> Unit)?

[Andreas Sinz]

you have to surround it with brackets

[oday]

ahhh cleva

[Andreas Sinz]

and to call it use myFun?.invoke()

[oday]

yes

[oday]

thank you

[SiebelsTim]

Depending on what you want, making it non nullable and supply an empty lambda {} for the null case might also be an option. I think it makes the code more readable in some situations.

[oday]

that’s how it was

[oday]

but then how will you check for emptyness?

[oday]

or non-validity for a better term, so as to know when not to invoke it

[Andreas Sinz]

depending on the underlying implementation, something like if(myFun != { }) myFun() could work, but nothing prevents you from accidentally invoking it. if its nullable, the compiler enforces that you check it first

[oday]

yea it’s safer with a null check

[SiebelsTim]

Calling an empty lambda is the same as not calling it. It doesn't do anything. You don't have to check for emptyness. Furthermore, I wouldn't check if it's equal to an empty lambda, I don't even know if performing equality checks on lambdas work the way you expect.
When you are guarding it with an if, i would definitely go for the null case.