Wrong type inference?

Support
1

Why it compile? int is List<int>, str is List<String>.

fun main() {
    val int = listOf(1, 2, 3)
    val str = listOf("1")
    val result = int.intersect(str)
    println(result)
}
1 Like
2

intesect generic parameter T is deduced as Any which is an ancestor of both Int and String.

It may seem awkward but lists of different types can have non empty intersection:

val l1:List<Number> = listOf(3, 1.2)
val l2:List<Any> = listOf("foo", "bar", 3)

Does this happen frequently? I don’t think so.

1 Like
3

Weird. Main question why it deduced to Any. In c# it will be compile error.

val r = listOf(1, "2", 3.0)
1 Like
4

Why it shouldn’t? This is a common thing that compiler tries to automatically cast types to their supertypes. See this example:

interface Serializer
object StringSerializer : Serializer
object IntSerializer : Serializer

val serializers = listOf(StringSerializer, IntSerializer) // type: List<Serializer>

I think such code is pretty clear and natural to everyone. It really does the same thing as listOf(1, "2", 3.0).

2 Likes
5

I think the OP has a point here; I don’t think they are worried that the common supertype is computed, but rather that this common supertype happens to be Any. Implicit cast to Any is reported in many places, and this looks like just another one of them.