Kotlin type-safe typealiases

Question

I use typealiases in my Kotlin code a lot, but I wonder if I can enforce type-safety on them.

typealias Latitude = Double
typealias Longitude = Double

fun someFun(lat: Latitude, lon: Longitude) {...}

val lat: Latitude = 12.34
val lon: Longitude = 56.78
someFun(lon, lat) // parameters are in a wrong order, but the code compiles fine

It would be nice if I could somehow prevent implicit casting between typealiases, helping to avoid such issues.

Of course, there is a problem, that the operations on basic types would be not available for typealiases, but it can be solved with extension functions (or casts).

I don't want to use data classes, holding a single field, because it seems a bit of overkill, especially for primitive types (or maybe I am wrong and they'll be optimized out?)

So the question: can I somehow enforce type-safety for typealiases?

Answer 1

Update for Kotlin 1.3

Inline classes are already available as of Kotlin 1.3 and currently are marked as experimental. See the docs

Original answer

Unfortunately you can't avoid this currently. There is a feature in progress - inline classes (#9 in this document), which will solve the problem with the runtime overhead, while enforcing compile time type-safety. It looks quite similar to Scala's value classes, which are handy if you have a lot of data, and normal case classes will be an overhead.