Hey everyone, I'm dabbling with extensions, and I'...

# arrow

[zsmb]

Hey everyone, I'm dabbling with extensions, and I'm trying to get something to work based on an example in the docs:

interface Eq<F> {
    fun F.eqv(b: F): Boolean
    fun F.neqv(b: F): Boolean = !eqv(b)
}

data class User(val id: Int) {
    companion object
}

@extension interface UserEq : Eq<User> {
    override fun User.eqv(b: User): Boolean = id == b.id
}

Now, I can make the neqv call work, as that extension is generated:

val user1 = User(1)
val user2 = User(2)

user1.neqv(user2)

However, I don't get an eqv extension generated. I did get an eq extension that I could then open a scope on with run, but this isn't very neat:

User.eq().run {
    user1.eqv(user2)
}

So... Is there something I could fix in my code to make Arrow generate the eqv extension that I could use like this?

user1.eqv(user2) // right now, unresolved reference: eqv

[kioba]

I tried with 0.8.2 and I have the same issue as you. Seems like it does not generate the eqv as extension on the User type. Just he Companion obbject going to be generated

fun User.neqv(b: User): Boolean = aaa.aaa.kioba.bbb.bbb.User.eq().run {
  [e-mail](b) as kotlin.Boolean
}

fun Companion.eq(): UserEq = object : aaa.aaa.kioba.bbb.bbb.UserEq {  }

[kioba]

with 0.8.2 I could end up generating the function with a workaround. Seems like the annotation will only generate the extension if the base interface has a default implementation. If you modify your EQ<F> interface according to this:

interface Eq<F> {
  fun F.eqvImp(b: F): Boolean
  fun F.eqv(b: F): Boolean = eqvImp(b)
  fun F.neqv(b: F): Boolean = !eqvImp(b)
}

it will generate the User.eqv function for you.
Edit: still trying to figure out the annotation processor why filtering out the functions with non default impl.

[zsmb]

Maybe this is the intended behavior, but I'm hoping there's something I'm doing wrong to make this happen.

[raulraja]

This seems like a bug, I checked the arrow instances in master and eqv is getting generated properly. For example for ListK:

@JvmName("eqv")
@Suppress(
        "UNCHECKED_CAST",
        "USELESS_CAST",
        "EXTENSION_SHADOWED_BY_MEMBER",
        "UNUSED_PARAMETER"
)
fun <A> Kind<ForListK, A>.eqv(EQ: Eq<A>, arg1: Kind<ForListK, A>): Boolean = arrow.data.ListK.eq<A>(EQ).run {
  [e-mail](arg1) as kotlin.Boolean
}

[raulraja]

I suggest you add an issue to arrow with a minimal repro example. It should always export that method.