Extension delegating property should work kotlinlang #getting-started

so a property that delegates an extension? i didn't know that was a thing. can that be used to dynamically implement interfaces on instantiating a class?

gcx11

06/23/2018, 5:10 PM

@Hullaballoonatic https://kotlinlang.org/docs/reference/extensions.html#extension-properties

Hullaballoonatic

06/23/2018, 5:11 PM

thanks!

i can't do delagation since i want to point to an interface property. not sure how extension property helps me here

i have an interface with a property called

scalingProperty

and i want to be able to implement this interface but allowing to name the property as something with context, like

volume

am i overcomplicating this? is that as easy as

var volume: Volume
    get() = scalingProperty
    set(v) {
        scalingProperty = v
    }

orangy

06/23/2018, 6:00 PM

yes, but

var YourInterface.volume : Volume

and the rest is as you wrote

You want to invoke it

instance.volume

, right?

Hullaballoonatic

06/23/2018, 6:00 PM

yes

i think i had it backwards

interface Liquid<T: ItemData> : Scale<Volume, T> {
    override var scalingProperty: Volume
        get() = volume
        set(value) {
            volume = value
        }
    
    var volume: Volume
}

orangy

06/23/2018, 6:13 PM

That would work too, of course, but I would make

scalingProperty

final, so that it wouldn’t be overriden further in hierarchy

Hullaballoonatic

06/23/2018, 6:14 PM

can't implement final in interface

orangy

06/23/2018, 6:15 PM

Ok, let me open an IDE 🙂

So, I was thinking along the lines that anything with

Volume

should have property `volume`:

interface Scale<TUnit, TData> {
    var scalingProperty: TUnit
}

interface Volume
object Barrel : Volume

var <TData> Scale<Volume, TData>.volume
    get() = scalingProperty
    set(value) {
        scalingProperty = value
    }

fun test(some: Scale<String, Int>, liquid: Scale<Volume, Int>) {
    some.volume = Barrel // error
    liquid.volume = Barrel // ok
}

✍️ 1

😄 1

Hullaballoonatic

06/23/2018, 6:25 PM

do you know if it is possible to dynamically implement varying interfaces on a class during instantiation?

orangy

06/23/2018, 6:29 PM

object : Volume {}

Kotlin is statically typed language, so no dynamic subtyping

Hullaballoonatic

06/23/2018, 6:30 PM

ah, shucks

orangy

06/23/2018, 6:32 PM

Nope, that rulz 🤘

👍 1

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