why is an Int not an Int inside an interface?

Issue

I have this function in side an interface

    interface test<Int>{
        fun printInt():Int {
            return 2}}

The error is: the integer literal doesn't conform to the expected type Int.

1. If I change the return type to kotlin.Int, the error goes away.

    interface test<Int>{
        fun printInt(): **kotlin.Int** {
            return 2}}

2. I don't use return, it works fine like this:

    interface test<Int>{
            fun printInt() = 2
    }

3. if I get the printInt function out of the interface, the compiler doesn't complain:

    fun printInt(): **Int** {
                return 2}

what are these Int#1 and kotlin.Int?

Solution

This declaration:

interface test<Int>

declares a generic interface, with a type parameter called Int. This is similar to how MutableList is a generic interface with a type parameter called E:

public interface MutableList<E>

Therefore, inside the interface, the unqualified name "Int" refers to the type parameter, (similar to how inside MutableList, E refers to the type parameter) not the kotlin.Int type.

Answered By - Sweeper