Is there a way to use `where` clause when defining `typealiases` ?

# announcements

[laimiux]

Is there a way to use where clause when defining typealiases ?

[LeoColman]

What do you want to accomplish?

[LeoColman]

Maybe not with that exact ordering, but tell us an example of what you want

[laimiux]

I’m exploring interface composition

interface HasId {
  val id: String
}

interface HasName {
  val name: String
} 

fun <T> doSomething(data: T): Unit where T : HasId, T : HasName {
  // whatever
}

This gets cumbersome when you have multiple functions. I would like to define typealias once and use it for multiple functions

typealias Data = HasId & HasName

[Zac Sweers]

what you want is similar to what this thread describes https://kotlinlang.slack.com/archives/C0B9K7EP2/p1589398414110200?thread_ts=1589398414.110200

[Mayank]

You can define a interface instead of typealias

interface Data: HasId, HasName

or use reified for type checking as demonstrated in this blog, the required part being https://gist.github.com/yenerm/4ff23c907b56fe72f5b32e51a1ae0f8e#file-reified-kt

[laimiux]

@Zac Sweers I do want that, but for another use case. For this case, I need a sort of a sum type that allows defining multiple interface constraints.

data class RootData() : HasId, HasName, HasProp1, HasProp2

The idea is to select only partial data without having to map from data type to another. So, I could select only HasId and HasProp1 without having to ask for the whole RootData object. The interface solution doesn’t work well because then RootData would need to implement Data interface which would couple data to all the places consuming it (I would prefer the data to not be aware where it is consumed).