Using java code i can use interface with a single method just by using the interface name, like this:

val x = SomeInterface { }

Thanks to SAM. However when i try the same thing on kotlin interface I'm forced to create an anonymous class:

val x = object : SomeInterface {
  fun someMethod() { }
}

If i instead create a type alias for it I can write it without the object ceremony but I've no way of specifying what it is:

typealias SomeInterface = (): Unit

// ...

val x = { }

Yes i know i can do

val x: SomeInterface = { }

But picture this situation:

val x: SomeInterface = when (foo) {
  "A" -> { { } }
  "B" -> { { } }
}

I need double

{

, which is horrible. I think it would be much better to be able to write;

val x = when (foo) {
  "A" -> SomeInterface { }
  "B" -> SomeInterface { }
}

Is there a way to do this or a way to improve the previous example?

I think you can declare top level function fun

SomeInterface(lambda): SomeInterface = lambda

Then you will be able to do what you want

Thanks for the tip, i can make it inline to remove any friction and just improve the code readability. Thanks!

alternatively you can add an invoke operator to the interfaces' companion object. I prefer this approach, but obviously you can't do that to a java class, though

@Hullaballoonatic I'm sorry I fail to understand what you mean do you mean something like:

interface SomeInterface {
  operator fun invoke(param: SomeParam): SomeResult
}

? or do you mean like this?

interface SomeInterface {
  fun doStuff(param: SomeParam): SomeResult
  companion object {
    operator fun invoke(lambda: SomeInterface): SomeInterface = lambda
  }
}

? If you meant any of those, I fail to see how they'd help in my situation / how to make use of them. Can you give an example of what you meant and how to use it? Thanks