With the Kotlin experimental features, is it possi...

# getting-started

[Kelvin Chung]

With the Kotlin experimental features, is it possible to implement an operator overload that only works within a certain context? Something like

interface Addition<T> {
  fun add(lhs: T, rhs: T): T
}
interface AdditionOp<T> {
  context(addition: Addition<T>)
  operator fun add(rhs: T): T = addition(this, rhs)
}

or are operator overloads locked to specific signatures and AdditionOp.add() is not possible?

[Nicolai C.]

Yes, that works perfectly fine, except the correct function name is plus not add. I have quite a few context-aware operator functions across a handful of my DSLs.

[Nicolai C.]

The only unsupported feature I've encountered so far with context parameters, is that you cannot get a callable reference to them. I'm not sure if there are plans to support them in the future, but I'd assume so.

[phldavies]

You also cannot currently use them with property delegation operators (getValue)

[Kelvin Chung]

Follow-up: suppose you have something like this:

object FooAddition : Addition<Foo>

interface AdditionOp<T> {
  context(addition: Addition<T>)
  operator fun plus(rhs: T): T = ...
}

class Foo : AdditionOp<Foo>

Given that FooAddition is a globally available singleton, would it be possible to invoke the + operator "context-free"? ie. without

context(FooAddition) { ... }

I imagine that this could be useful in certain situations involving value classes.