I'm guessing no, but is it possible to do something cool like make an type implement an interface vi...

# announcements

[Matt Thiffault]

I'm guessing no, but is it possible to do something cool like make an type implement an interface via extension functions? Eg. can I add a .close() extension to something and then pass it as AutoCloseable?

[nwh]

There was a KEEP proposal for this, but I can't seem to find it, unfortunately. Hopefully someone else know where it's ended up

[streetsofboston]

It's KEEP-87 https://github.com/Kotlin/KEEP/pull/87

[Matt Thiffault]

Haha, nice. I'm amused that it's Raul's proposal since it's Arrow that I'm interacting with.

[nwh]

I feel like that proposal got a bit wild. I started seeing the with keyword in arguments and stuff and found myself very lost

[nfrankel]

actually, it’s quite easy without it
i had a class called JetInstance
which has a shutdown method
and wanted to use use() on it
to automatically close() it
with delegate and extension method, this is a breeze:

class CloseableJet(private val instance: JetInstance) : Closeable, JetInstance by instance {
    override fun close() {
        shutdown()
    }
}

fun JetInstance.withCloseable() = CloseableJet(this)

now:

Jet.newJetClient().withCloseable().use {
    it.newJob(pipeline(), config)
}

[Matt Thiffault]

Ok that "by instance" trick is awesome and I didn't know it exits, thank you!

[streetsofboston]

Yup, Kotlin’s way of doing some mix-ins and traits 🙂