Playing with `values classes` right now. We’re usi...

# getting-started

[Jérémy CROS]

Playing with values classes right now. We’re using Location objects a lot in our app and I thought they would be a very good fit to replace longitude: Double et latitude: Double.
After a couple hours trying to slowly replace them in our codebase, looks like they are a lot less convenient than I expected...
In particular, is there no simple way to do some basic math operations on them out of the box?
For exemple, doing some area bounds computation like:

val averageLatitude =
    (area.bottomLeft.latitude + area.topLeft.latitude + area.bottomRight.latitude) / 3

Looks like I have 2 options right now:
• call .value on all latitude objects
• follow the suggestion and create a Latitude.plus member function
Am I missing anything?

[Kristian Nedrevold]

Maybe something like

interface Coord<T> {
    val value: T
}

operator fun Coord<Double>.plus(other: Coord<Double>) = this.value + other.value

@JvmInline
value class Lat(override val value: Double) : Coord<Double>

@JvmInline
value class Long(override val value: Double) : Coord<Double>

fun main() {
    val lat = Lat(10.0)
    val long = Long(10.0)

    val sum = lat + long
}

Would be ok?

[Jérémy CROS]

hmmm, slightly better than my second option since then, I don’t have to define plus for both latitude and longitude, thanks for the suggestion 🙂
thinking on giving up on it anyway 😕 the feature looked promising but it’s not quite there yet, just learned that it doesn’t work with room for example 😞

[Klitos Kyriacou]

This doesn't look right to me. Having Long and Lat share the same interface means you can add a longitude to a latitude, which would be meaningless. You wouldn't want to do that.

[Klitos Kyriacou]

You can probably fix that using value class Lat(override val value: Double) : Coord<Lat> or similar

[Jérémy CROS]

I see your point, thank for the suggestion 🙂 🙏

[phldavies]

The downside is you lose your type safety as Lat.plus(Lat) -> Double. That may or may not be desired. By defining twice (should only really need to be written once… and copy/paste/search/replace should get you there quickly) you gain Lat.plus(Lat) -> Lat - you can also still have Lat.div(Int) -> Double etc as required. One option to avoid the pain of writing this might be to look into KSP to generate some math operations automagically.