Support Kotlin higher-order functions/lambdas

NativeScript supports marshalling Java bytecode generated by Kotlin. But Kotlin has a way to specify that a function takes another function in a much better way than Java.

Like this:

fun myfun(callback: (arg: String) -> Void)

It compiles to something like

public final void myfun(@org.jetbrains.annotations.NotNull final kotlin.jvm.functions.Function1<? super String, Void> callback)

where Function1 is a class containing an invoke method. Depending on how many args the function takes, it'll be called Function2, Function3 and so on.

Interacting with myfun from JavaScript would be done this way:

myfun(new kotlin.jvm.functions.Function1({ invoke: () => console.log("invoked") }))

It would be so cool if NativeScript supported Kotlin-functions out of the box, so the callback wouldn't need to be wrapped in FunctionX and myfun could be run via myfun(() => console.log("invoked")). This would make it easier to align with an Objective-C library, where blocks are supported.

To support Kotlin, my app.gradle currently looks like this:

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.3'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.2.30"
    }
}

dependencies {
  compile fileTree(dir: "libs", include: ["*.jar"])
  compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:1.2.30"
}

android {  
  defaultConfig {  
    generatedDensities = []
    applicationId = "org.nativescript.test"  
  }  
  aaptOptions {  
    additionalParameters "--no-version-vectors"  
  }  
} 

Non vengono indicati file o test del repository. Inizia tracciando il marshalling del bytecode Java di NativeScript Android e il modo in cui sono rappresentati kotlin.jvm.functions.Function1, Function2 e le arità superiori; confrontalo con il percorso esistente di wrapping dei callback JavaScript. Il lavoro è completato quando i parametri delle funzioni Kotlin possono ricevere direttamente callback JavaScript senza costruire manualmente istanze di FunctionX.