CODEWITHSUNDEEP
kotlin
Bula
Bula

Reputation: 2792

Simple SAM needs conversion to anonymous object

I have the following simple interface

interface A {
    fun move(s:Boolean): Int
}

I have the following class

class X{
    fun draw (x: A): String{
        return "A"
    }

    fun main() {
      val temp = A {
          s -> 100
      }
      val a = draw ( { x -> 100} )
    }
}

However both temp and a fail to be declared. temp complains and the suggested fix is to convert to an anonymous object as follows (which defeats the whole purpose of using a SAM?)

val temp = object : A {
        override fun move(s: Boolean): Int {
            return 100
        }
    }

a complains about a type mismatch. My question is why does this simple SAM fail? The method signature is the same.

Upvotes: 1

Views: 107

Answers (2)

RobCo
RobCo

Reputation: 6495

Currently Kotlin only has SAM conversion for interfaces defined in Java.
For pure Kotlin code you're supposed to use a function type such as:

typealias A = (s: Boolean) -> Int

However, the syntax you expected will be supported in Kotlin 1.4 with interface defined as fun interface.
As announced here: What to Expect in Kotlin 1.4 and Beyond
and tracked as KT-7770

Upvotes: 1

Raman
Raman

Reputation: 19595

Kotlin 1.4 has support for SAM conversions for Kotlin interfaces, in addition to the Java interface SAM conversion available in previous versions. See:

With 1.4, you do need to define your interface as a "functional" interface:

fun interface A {
    fun move(s:Boolean): Int
}

Upvotes: 0

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