Hey what s wrong here I don t get any syntax error but compi kotlinlang #announcements

Cause: Label wasn't found during iterating through instructions
Element is unknownThe root cause was thrown at: LabelNormalizationMethodTransformer.kt:148

-.kt

Oh, this also causes a compilator crash:

class foo(var bar : String)

fun main() {    
    var baz : foo? = foo("test")
    baz?.bar += "test"
}

streetsofboston

04/19/2019, 7:03 PM

Is it because may be trying to assign a value to a

null

property…?

baz?.bar

could be null. Then you may wind up with

null += test

. This should not compile. But instead of a compiler error you get a compiler crash…

I get the same error

Sebastian Krajewski

04/19/2019, 7:07 PM

But ?. operator ensures that you work on an instance

streetsofboston

04/19/2019, 7:08 PM

What you’d want is

baz?.let { it.bar += test }

This is a simplified version of the bug you found:

class Container(
    var value : String = ""
)

fun bug() {
    val container : Container? = null
    container?.value += "2"
}

It seems to come from the

+=

operator with an optional/nullable left-hand side expression

Sebastian Krajewski

04/19/2019, 7:19 PM

Yep, because

?.plus()

seems to work

But if value is non nullable and property is called safely, why it needs safe call?

streetsofboston

04/19/2019, 7:21 PM

I think since a

String

is a immutable class, the

+=

is not a

plusAssign

. It probably rewrites it a

object = object + param

, which may fail….

Rewriting it manually works….

class Container(
    var value : String = ""
)

fun bug() {
    val container : Container? = null
    container?.value = container?.value + "2"
}

You should file a bug.

Sebastian Krajewski

04/19/2019, 7:24 PM

It is already filled

💯 1

streetsofboston

04/19/2019, 7:26 PM

Do you have the link to the bug? I’d love to share it with my teams here. Thank you!

Sebastian Krajewski

04/19/2019, 7:26 PM

It was filled by my friend: https://youtrack.jetbrains.com/issue/KT-31135

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