title: Error when passing a Swift implementation of a Kotlin interface to a Kotlin method
body: <p>I'm doing some experimenting with Kotlin Native on iOS, and one thing I wanted to try was having a Swift implementation of a Kotlin-defined interface. However, I end up crashing when I try to pass that Swift object back up to the Kotlin code.</p>
  
  <p>I'm using the kotlin gradle plugin version 1.2.30 and kotlin native version 0.6.1</p>
  
  <p>A minimal example follows. The Kotlin code is being compiled to a framework with the name KotlinCommon, which is then included in the xcode project.</p>
  
  <p>DemoClass.kt</p>
  
  <pre><code>class DemoClass {
      fun process(dependency: Dependency) {
          dependency.foo()
      }
  }
  
  interface Dependency {
      fun foo()
  }
  </code></pre>
  
  <p>SwiftDependency.swift</p>
  
  <pre><code>import KotlinCommon
  
  class SwiftDependency : KotlinCommonDependency {
      func foo() {
          NSLog("hello")
      }
  }
  </code></pre>
  
  <p>Then, from my iOS UI I try to run</p>
  
  <pre><code>let module = KotlinCommonDemoClass()
  let dependency = SwiftDependency()
  module.process(dependency: dependency)
  </code></pre>
  
  <p>The third line causes a crash with the following error:    </p>
  
  <pre><code>*** NSForwarding: warning: object 0x101858d20 of class 'KotlinNativeDemo.SwiftDependency' does not implement methodSignatureForSelector: -- trouble ahead
  Unrecognized selector -[KotlinNativeDemo.SwiftDependency toKotlin:]
  </code></pre>
  
  <p>Is this use-case not supported by Kotlin Native? Or could there be something I'm configuring wrong?</p>