Hey all. I'm new. I was fiddling around with generics and type inference using functional approaches, but I'm a little confused about type inference logic for second order functions. Given

fun <E> firstOrderFnWithSecondOrderTypeInference() = { value: E -> value }

, attempting to

firstOrderFnWithSecondOrderTypeInference()(42)

gives me a type inference error:

Type inference failed: Not enough information to infer parameter E in  fun <E> firstOrderFnWithSecondOrderTypeInference( ) : (E) → E Please specify it explicitly.

firstOrderFnWithSecondOrderTypeInference<Int>()(1234)

works because there's no type inference for

E

of the second rank function. I guess what I'm looking for is a why it's like this so I can understand the language a bit better. I know that C++ is the same way, same with Typescript, so I wonder if there's an underlying reason.

I think it is not about second order functions but about call chains. For example here compiler cannot infer type too:

mutableListOf().add(1)

But maybe compiler will be smarter with new type inference (experimental in 1.3):

Oh wow! Well there you go. Thank you. This is a really good video!