is it possible to determine if a lambda type has a...

# reflect

[jw]

is it possible to determine if a lambda type has a receiver or just a normal argument from parsing a function parameter's type? i'm in the process of switching from reflect to metadata-jvm (or maybe fully blown UAST) but looking for a quick workaround until then

[jw]

The KParameterImpl has the KFunctionImpl in its private callable property, but I can't get access to that as far as I can tell

[jw]

Oh nevermind that's the enclosing function

[ephemient]

without metadata, I believe (T) -> R and T.() -> R are represented by the same kotlin.Function1<T, R> which is erased to kotlin.jvm.internal.Function1 on JVM: https://github.com/JetBrains/kotlin/blob/master/spec-docs/function-types.md

[jw]

They are, but kotlin-reflect uses metadata, right? That's why it's like 20MiB or whatever because it embeds all the protos.

[ephemient]

oh I thought you were looking for a way to do it without metadata-jvm. hmm, seems like you should be able to do it with metadata but it's not obvious to me how

[jw]

yeah i think i just need to fully abandon "runtime" reflection and switch to metadata-jvm parsing of the class files

[jw]

solves more problems than just this current one

[ephemient]

kotlin.reflect.typeOf<Unit.() -> Unit>() == kotlin.reflect.typeOf<(Unit) -> Unit>()

I don't think kotlin-reflect exposes any difference :-/

[jw]

I think you can!

type.annotations.any { it.annotationClass == ExtensionFunctionType::class }

[ephemient]

>>> fun f(block: (Unit) -> Unit) = Unit
>>> fun g(block: Unit.() -> Unit) = Unit
>>> ::f.parameters.single().type.annotations
res0: List<Annotation> = []
>>> ::g.parameters.single().type.annotations
res1: List<Annotation> = [@kotlin.ExtensionFunctionType()]
>>> ::f.parameters.single().type == ::g.parameters.single().type
res2: Boolean = true
>>> typeOf<Unit.() -> Unit>().annotations
res3: List<Annotation> = []

… ok, I guess that works, but it's kinda surprising

[jw]

Somewhat ironically I learned about it from reading the kotlinx-metadata-jvm discussion https://discuss.kotlinlang.org/t/announcing-kotlinx-metadata-jvm-library-for-reading-modifying-metadata-of-kotlin-jvm-class-files/7980/27

[ephemient]

looks like there's also @kotlin.ContextFunctionTypeParams(count: Int) and @kotlin.ParameterName(name: String) (the latter on the type parameters to FunctionN<>), and the lambda type also seems to know if it's a suspend function, but I'm not sure how that's determined

[ephemient]

that's actually a pretty decent amount of information without having to pull kotlinx-metadata-jvm yourself