kotlin: how to use KProperty2?

Issue

I understand that KProperty1 represents a property on a class, such as MyClass::myProperty.

I'm having trouble understand how KProperty2 should be used, or even what the concrete use case is for that pattern?

Thanks

Solution

It's as documentation states for properties that take two receivers like extension property declared in a class.

Do note that calling extension functions and properties declared within class has be done within that class itself or through scoping functions (as done in sample below with run {}):

Example:

data class Foo(val tag : String) {
    val Int.echo
        get() = "Im extension on $this within ${this@Foo}"
}

fun propTest(){
    val foo = Foo("Baz")

    foo.run {
        println(5.echo)    // prints Im extension on 5 within Foo(tag=Baz)
    }

    val tagRef : KProperty1<Foo, String> = Foo::tag
    val echoRef : KProperty2<Foo, Int, String> = Foo::class.declaredMemberExtensionProperties.first() as KProperty2<Foo, Int, String>

    println(echoRef.get(foo, 7))  // prints Im extension on 7 within Foo(tag=Baz)
}

I don't know if it's possible to directly reference those extensions (Int::echo within class scope just causes error) that's why I used declaredMemberExtensionProperties (which is actually a List<Kproperty2<Foo, *, *>>) to fetch it.

Answered By - Pawel