Has there ever been discussion for generation of backing fields for interfaces? Similar to how this ...

# language-evolution

[asdf asdf]

Has there ever been discussion for generation of backing fields for interfaces? Similar to how this would work in Scala:

Untitled.scala

[Casey Brooks]

As much as I personally like the idea of “traits”, they’re not really necessary in Kotlin. It requires a bit more boilerplate, but you can achieve the same thing using interface delegation. For example:

class Foo :
    A by ADelegate(),
    B by BDelegate()

interface A {
    var a: String
}
class ADelegate : A {
    override var a: String = ""
}

interface B {
    var b: String
}
class BDelegate : B {
    override var b: String = ""
}

[Ben Woodworth]

Or possibly even nicer from the usage side, using invoke for a pseudo-constructor

Untitled.cpp

[Ben Woodworth]

Though I'd argue the Kotlin way is to prefer composition over inheritance, and do something like this

(except probably with better naming. i only used the trait-inspired naming convention for clarity)

Untitled.cpp

[elizarov]

It looks like you are asking for something like this: https://youtrack.jetbrains.com/issue/KT-52462/Optionally-overridable-default-values-for-interface-var-properties

[asdf asdf]

Yeah, I find the main use case of it to be adding fields to already existing interfaces without going through every implementor and adding the override with default there