Typealias with intersectable types

user_3322533 0
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Let's say I have an interface HasId and another HasResponsiblePerson. I am now interested in an instance that implements both.

i.e.

typealias AssignableEntity = HasId & HasResponsiblePerson

class Foo {

   val entity: AssignableEntity
}

But this fails because

Intersection types are only supported for definitely non-nullable types: left part should be a type parameter with nullable bounds

I could, of course, just define a new interface

interface AssignableEntity: HasId, HasResponsiblePerson

but then I have to define new interfaces every time I come across a new combination of interfaces I am interested in, and we end up with a ton of mostly useless interfaces.

Is there a way to do what I want?

kotlin
2 Answers

Intersection and union types are not denotable in Kotlin at the moment: https://youtrack.jetbrains.com/issue/KT-13108

As the message tells you, a first step in this direction was taken for T & Any to represent definitely non-nullable types, but it's not yet available for general intersections.

In the meantime, you can use a dedicated interface, pass multiple arguments, or return a compound class as @Ivo suggested.

user_15408180

It's not really an answer to the question I guess, but alternatively you maybe just do

class Foo {
   val idEntity: HasId
   val responsibleEntity: HasResponsiblePerson
}

Keep them in separate variables. And assign them the same object. In your code refer to the one that's relevant. This also makes it more flexible and makes you able to actually use different objects for it. If you specifically don't want them to be different you could maybe throw an error in that case, but admittedly that's maybe not a clean solution.

user_15148610
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