I’d love to see reified constructors so that I hav...

# language-proposals

[Marc Knaup]

I’d love to see reified constructors so that I have all information about generic type parameters. I’d use them to replace problematic Java type token hacks when writing BSON/JSON/GraphQL serializer base classes. And it would even work in multiplatform!

open class Generic<T: Any> private constructor(
   private val type: KType
) {

   inline <reified T> constructor():
      this(type = typeOf<T>())
}

Does anyone else have good use cases for this?

[Marc Knaup]

https://youtrack.jetbrains.com/issue/KT-13127

[spand]

Do you gain anything else than some sugar so you wont have to write the companion invoke function yourself?

[Marc Knaup]

This won’t work with companions

[Marc Knaup]

class SomeClass: Generic<List<String?>>()

[drieks]

I'm using this as a workaround:

@Suppress("FunctionName")
inline fun <reified T> SomeClass(): SomeClass<T>() {
  return SomeClass(typeOf<T>())
}

class SomeClass<T>(val type: KType)

(I see you already mentioned it before in the ticket)

[Marc Knaup]

I would have to do that for hundred of classes 😅
Also, in my current use case all are object, so that workaround won’t work.

My current workaround is that each object has to call an extension function during initialization which allows me to generate a KType

[efemoney]

This got me thinking but maybe we can have a fun constructor(): SomeClass {...} that generates a ‘static’ (or top level in kotlin terms) function with same name as class. Should be possible to make it inline and have reified type params