I have this line of code ``` val foo = gitl...

# announcements

[pavel]

I have this line of code

val foo = gitlabEvent.webhookEvent.objectAttributes != null && gitlabEvent.webhookEvent.objectAttributes.action == Action.OPEN

gitlabEvent and webhookEvent are non-nullable. objectAttributes is nullable. The compiler is telling me Smart cast to 'ObjectAttributes' is impossible, because 'gitlabEvent.webhookEvent.objectAttributes' is a complex expression. I thought smart casting was smarter than that 😞

[dpk]

is webhookEvent provided by a separate module or some dependency? if so, that’d explain the error

[pavel]

no, they are in the same compilation unit

[pavel]

webhookEvent is a data Class. So are objectAttributes

[pavel]

interface GitlabEvent {
    val webhookEvent: WebhookEvent
    val filter: String

    fun buildSlackMessage(): SlackMessage
}

[pavel]

@JsonIgnoreProperties(ignoreUnknown = true)
data class WebhookEvent(
    @JsonProperty("object_kind") val objectKind: WebhookEventType,
    val project: Project,
    val user: User,
    @JsonProperty("object_attributes") val objectAttributes: ObjectAttributes? = null,
    @JsonProperty("merge_request") val mergeRequest: MergeRequest? = null,
    val commit: Commit? = null,
    val issue: Issue? = null,
    val snippet: Snippet? = null
)

[pavel]

@JsonIgnoreProperties(ignoreUnknown = true)
data class ObjectAttributes(
    val id: Int,
    val action: Action = Action.UNKNOWN,
    val title: String = "",
    val url: String,
    val iid: Int,
    val note: String = "",
    @JsonProperty("noteable_type") val noteableType: NoteableType = NoteableType.UNKNOWN
)

[dpk]

dunno. i’m on 1.3.10, can’t reproduce it with this code:

val x = Fred(Bar(Foo("xyz")))

	data class Foo(val label: String)
	data class Bar(val foo: Foo? = null)
	data class Fred(val bar: Bar)

    fun doTheFoo() { val y = x.bar.foo != null && x.bar.foo.label == "xyz" }

i do get exactly that error if i declare x with var, but it looks like that’s not the case here. stumped.

[pavel]

That project is still on 1.2. I upgraded to 1.3.10 and I am still getting that, but maybe I missed something…

[pavel]

interestingly enough, this

val webhookEvent = gitlabEvent.webhookEvent
val foo = webhookEvent.objectAttributes != null && webhookEvent.objectAttributes.action == Action.OPEN

compiles

[dpk]

ahh, of course, the interface:

val x: Fred = FredImpl(Bar(Foo("xyz")))

	data class Foo(val label: String)
	data class Bar(val foo: Foo? = null)
	interface Fred { val bar: Bar }
	data class FredImpl(override val bar: Bar) : Fred
    fun doTheFoo() { val y = x.bar.foo != null && x.bar.foo.label == "xyz" }

demonstrates the problem. i ain’t smart enough to know the cause, but there ya go, i see the same thing now.

[pavel]

👍

[pavel]

maybe it’s because the interface could have an implementation in a different language in an external module and do bad things?

[karelpeeters]

Or just in the same module, what if someone changes the implementation? Other classes' smartcasts shouldn't suddenly stop working.

[pavel]

well, it’s a val. It can’t magically become a var if overriden

[karelpeeters]

val myNonVar: String?
    get() = if (Random().nextBoolean()) "test" else null

[pavel]

that’s just evil 😞

[pavel]

maybe I can rewrite that as sealed class. Then it should work

[pavel]

🤔

[karelpeeters]

This is a dumb example of course, but this also happens in other situations. `val`s that offer an immutable view on another mutable property for example.

[pavel]

Yeah, makes sense.

[stevecstian]

This is actually a good question that could help people understand val further.

[aarjav]

Just curious, would the ?. still work? As in val foo = gitlabEvent.webhookEvent.objectAttributes?.action == Action.OPEN

[pavel]

it would. gitlabEvent.webhookEvent.objectAttributes?.action might return null, and it’s perfectly valid to compare null with other stuff