Hi! I want to do something if a `java.io.File` variable is null or not readable. In Java this vould ...

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[thecipster]

Hi!
I want to do something if a java.io.File variable is null or not readable. In Java this vould be

if (myFile == null || !myFile.canRead()) {
    // error!
}

which works always because of short-circuit evaluation.
IntelliJ translates the above code to:

if (simDesc == null || !simDesc!!.canRead()) {
    // error!
}

which is a bit ugly IMHO.
Any idea on making it more idiomatic?

[kirillrakhman]

thecipster: it seems simDesc is not a local variable but a mutable property. either save the value to a local variable, make the property immutable (val) or use some tricks like simDesc.takeIf { it.canRead() }?.let { /* do stuff */ }

[uhe]

I kinda feel like the current state of dealing with Boolean returning methods/properties on nullable objects is not very satisfying

[thecipster]

@kirillrakhman, @uhe thanks for the reply.
Unfortunately simDesc must be a mutable property (var simDesc: File? = null) because Java library.
The trick with takeIf is nice but hardly more readable 🙂.
I think that in this case the compiler knows enough to avoid the !! operator.

[uhe]

you can't avoid it. it's perfectly possible that simDesc is null on the second branch

[kirillrakhman]

it could be set to null on a different thread

[kirillrakhman]

like I said, you can save the value to a local variable

[thecipster]

OK now i see it, i wasn't considering multithreading issues

[kirillrakhman]

also you can do if (simDesc?.canRead() != true) but that won't help you, if you need to access the value again

[kirillrakhman]

see https://kotlinlang.org/docs/reference/idioms.html#consuming-a-nullable-boolean

[thecipster]

I just tried with copying to a local variable and indeed the compiler is smart enough to consider short-circuit evaluation and removes the !!.
Thanks a lot! 👍

[kirillrakhman]

you can read up on smart casts here: https://kotlinlang.org/docs/reference/typecasts.html