Type Inference on Function Reference?

Support
1

Hello, I’ve been struggling to understand why given the 2 snippets below, the first one compiles but the second one gives a type inference error.

First Snippet:

class A

class B

fun toB(a: A) = B()

fun List<A>.toB(): List<B> = this.map { toB(it) }

Second Snippet:

class A

class B

fun toB(a: A) = B()

fun List<A>.toB(): List<B> = this.map(::toB)
2

Thanks, filed an issue: https://youtrack.jetbrains.com/issue/KT-31630. The error is fixed in the experimental new inference algorithm, learn more on how to try it here: Kotlin 1.3.40 Early Access Preview

3

Thanks, look forward to it being fixed in stable!

4

I was under the impression that the compilation is still using the old type inference:

So changing to the 1.3.40 eap build wouldn’t actually help. You would still need to enable the new type inference for compilation.

5

That’s exactly right, thank you. To enable it on compilation you have to add a compiler argument -XXLanguage:+NewInference.