Please direct me to the right channel, but here’s ...

# getting-started

[Endre Deak]

Please direct me to the right channel, but here’s the question:

// this delegation works

interface A { fun foo() }
interface B { fun bar() }

class AImpl() : A { override fun foo() = println("default foo") }
class BImpl(private val a: AImpl) : B, A by a { override fun bar() = println("bar") }

// ==============

// how could I do a delegation for an inherited interface?
interface A { fun foo() }
interface B : A { fun bar() }

class AImpl() : A { override fun foo() = println("default foo") }
// no idea how to delegate
class BImpl(private val a: AImpl) : B by a { override fun bar() = println("bar") } // ?

[Ruckus]

class BImpl(private val a: AImpl): B, A by a { ... }

[Endre Deak]

I think what I’m looking for here is partial interface implementation delegation

[Endre Deak]

not sure if it’s possible in Kotlin at all

[Ruckus]

Why? The example I gave did exactly what you asked, and it is way less cryptic/confusing.

[Endre Deak]

I don’t want BImpl to have an explicit inheritance from A, I’d like to achieve that through B if possible. And therefore, a partial delegation would be required

[Ruckus]

But that's not what the a parameter is.

[Stephan Schroeder]

yeah, I'm with Ruckus. Inheritance is explicit in Kotlin (in order for BImpl to implement A , it has to be explicit about it). Ruckus' solution to generate default proxy calls to a parameter is as close as you can get to what you want.

[Endre Deak]

thanks for the feedback. I discussed this in the language propoosals channel as well: https://kotlinlang.slack.com/archives/C0B9K7EP2/p1632516626019100