AssertionError: assertion failed with intersections of method type refinements #8736
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Given that it seems we won't be able to support this (#8822), I've attempted to replicate it using unions and match types, it seems to work OK: trait Rec[K <: String] { self =>
protected val map: Map[String, Any]
type ValueOf[A <: K]
def get(k: K): ValueOf[k.type] = map(k).asInstanceOf
def +[K1 <: String](that: Rec[K1]): Rec[K | K1] {
type ValueOf[A <: K | K1] = A match {
case K => self.ValueOf[A]
case K1 => that.ValueOf[A]
}
} = new Rec[K | K1] {
protected val map = self.map ++ that.map
type ValueOf[A <: K | K1] = A match {
case K => self.ValueOf[A]
case K1 => that.ValueOf[A]
}
}
}
object Rec {
def field[S <: String & Singleton, V](s: S)(v: V) : Rec[s.type] {
type ValueOf[K <: s.type] = K match {
case s.type => V
}
} = new Rec[s.type] {
protected val map = Map(s -> v)
type ValueOf[K <: s.type] = K match {
case s.type => V
}
}
}
@main def Test = {
val rec = Rec.field("k")("Str") + Rec.field("v")(0) + Rec.field("z")(true)
def res1: String = rec.get("k")
def res2: Int = rec.get("v")
def res3: Boolean = rec.get("z")
println((res1, res2, res3))
} |
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@smarter Unfortunately this type, and probably match types in general, cannot be widened, e.g. this function cannot be applied to def getZ[S >: "z", V](r: Rec[S] { type ValueOf[A <: S] = A match { case "z" => V } }): V =
r.get("z")def res3: Boolean = getZ(rec)Error: There's another way to formulate this, with extension methods, that one seems to work well. I thought import scala.language.{dynamics, implicitConversions}
class Rec[K <: String, +V](protected val map: Map[String, Any]) extends Dynamic
object Rec {
def field[V](s: String)(v: V): Rec[s.type, V] = new Rec[s.type, V](Map(s -> v))
implicit class RecOps[R <: Rec[_, _]](private val self: R) extends AnyVal {
def get[V](k: String)(implicit ev: R <:< Rec[k.type, V]): V = self.map(k: k.type).asInstanceOf[V]
def selectDynamic[V](k: String)(implicit ev: R <:< Rec[k.type, V]): V = get(k: k.type)
def ++[R1 <: Rec[_, _]](that: R1): R with R1 = new Rec(self.map ++ that.map).asInstanceOf[R with R1]
}
}
def getZ[V](r: Rec["z", V]): V = r.z
@main def Test = {
val rec = Rec.field("k")("Str") ++ Rec.field("v")(0) ++ Rec.field("z")(true)
def res1: String = rec.k
def res2: Int = rec.v
def res3: Boolean = getZ(rec)
println((res1, res2, res3))
} |
This one works :) def getZ[S >: "z" <: String](r: Rec[S]): r.ValueOf["z"] =
r.get("z") |
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I tried the original code using function types instead of methods for object App extends App {
trait Rec0[K <: String] {
private[App] val map: Map[String, Any]
def get: (k: K) => Any
}
def Rec0(map0: Map[String, Any]) = new Rec0[String] {
val map = map0
def get: (k: String) => Any = map(_)
}
type Rec[K <: String, V0] = Rec0[K] { def get: (k: K) => V0 }
def field[V](s: String)(v: V): Rec[s.type, V] = Rec0(Map(s -> v)).asInstanceOf[Rec[s.type, V]]
implicit class RecOps[R <: Rec0[_]](has: R) {
def +[K1 <: String, V1](that: Rec[K1, V1]): R with Rec[K1, V1] = Rec0(has.map ++ that.map).asInstanceOf[R with Rec[K1, V1]]
}
def rec:
Rec["k", String]
with Rec["v", Int]
with Rec["z", Boolean]
= {
field("k")("Str") +
field("v")(0) +
field("z")(true)
}
def res1: String = rec.get("k")
def res2: Int = rec.get("v")
def res3: Boolean = rec.get("z")
// error
// def res4: Boolean = rec.get("nofield")
println((res1, res2, res3))
}Dotty complained: I tried adding the import just to see what happened, but it resulted in a runtime crash: @smarter I guess something should be done about it, no? The error suggestion was probably misleading, but adding the import should not create unsoundness. |
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Please open a separate issue for that, sounds like structural types that return lambdas are just not handled correctly at all |
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The following code compiles under Scala 2, all the way back to 2.11.12 (with literal type signatures omitted), but fails to compile in Dotty.
Scala 2 Scastie: https://scastie.scala-lang.org/yq2w0NDqQTm9VboAjm0Dqg
Dotty Scastie: https://scastie.scala-lang.org/JzTLvfBrRbGkKdIa8NrQNA
Minimized code
Output
Expectation
Expected compilation success
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