I'd like to be able to write `val a by delegate1(...

# announcements

[CLOVIS]

I'd like to be able to write

val a by delegate1() and delegate2()

I'm expecting it to have to define

infix fun Delegate.and(other: Delegate): Delegate {...}

But since delegation is defined on the presence of methods, and not on the inheritance from an interface, I don't know how to do it :/

[Nikky]

you might need to write val a by (delegate1() and delegate2())
and then the returned object/instance from and just needs to have the correct functions for delegation

[Nikky]

the methods are lined out here: https://kotlinlang.org/docs/reference/delegated-properties.html

[CLOVIS]

@Nikky If the function ‘and' takes two Any, then I can't call getValue on the objects to combine them

[CLOVIS]

And since there's no interface for delegates, I can't put anything else than Any?

[Tobias Berger]

just to check if I understood right: you're trying to create an extension function that can somehow combine any 2 delegates and your problem is that delegates don't need to implement a specific interface you could use as a receiver/parameter

[CLOVIS]

Yes, exactly

[CLOVIS]

I guess it's possible to cheat and implement this without combining delegates, I'm mostly doing this out of curiosity to what is possible and what isn't

[Tobias Berger]

I don't think there is any way to do exactly that in kotlin (I guess it would require something like implicit classes or C-style generics).
If you only need to use this with delegates you wrote yourself, you could use ReadOnlyProperty and ReadWriteProperty interfaces, but most default delegate implementations don't extend those.

[CLOVIS]

Hm.

[CLOVIS]

I don't understand why the language designers chose not to use inheritance here, it seems weird that that's the only place in the language that doesn't take advantage of it

[Tobias Berger]

well, it's not really the only place. basically all operator functions work without interfaces

[Nir]

C-style generics?

[Nir]

C++ style I guess?

[Tobias Berger]

sure, sorry