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Issue 2891 - Ambiguous Vector instances (typelevel#3100)
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* Changed precedence of kernel instances for Vector

* Fixed also List and Queue
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Filippo Mariotti authored and LukaJCB committed Oct 18, 2019
1 parent 1f81050 commit e766998
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Showing 6 changed files with 52 additions and 12 deletions.
10 changes: 6 additions & 4 deletions kernel/src/main/scala/cats/kernel/instances/ListInstances.scala
Original file line number Diff line number Diff line change
Expand Up @@ -13,14 +13,16 @@ trait ListInstances extends ListInstances1 {
}

private[instances] trait ListInstances1 extends ListInstances2 {
implicit def catsKernelStdPartialOrderForList[A: PartialOrder]: PartialOrder[List[A]] =
new ListPartialOrder[A]

implicit def catsKernelStdHashForList[A: Hash]: Hash[List[A]] =
new ListHash[A]
}

private[instances] trait ListInstances2 {
private[instances] trait ListInstances2 extends ListInstances3 {
implicit def catsKernelStdPartialOrderForList[A: PartialOrder]: PartialOrder[List[A]] =
new ListPartialOrder[A]
}

private[instances] trait ListInstances3 {
implicit def catsKernelStdEqForList[A: Eq]: Eq[List[A]] =
new ListEq[A]
}
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10 changes: 6 additions & 4 deletions kernel/src/main/scala/cats/kernel/instances/QueueInstances.scala
Original file line number Diff line number Diff line change
Expand Up @@ -13,14 +13,16 @@ trait QueueInstances extends QueueInstances1 {
}

private[instances] trait QueueInstances1 extends QueueInstances2 {
implicit def catsKernelStdPartialOrderForQueue[A: PartialOrder]: PartialOrder[Queue[A]] =
new QueuePartialOrder[A]

implicit def catsKernelStdHashForQueue[A: Hash]: Hash[Queue[A]] =
new QueueHash[A]
}

private[instances] trait QueueInstances2 {
private[instances] trait QueueInstances2 extends QueueInstances3 {
implicit def catsKernelStdPartialOrderForQueue[A: PartialOrder]: PartialOrder[Queue[A]] =
new QueuePartialOrder[A]
}

private[instances] trait QueueInstances3 {
implicit def catsKernelStdEqForQueue[A: Eq]: Eq[Queue[A]] =
new QueueEq[A]
}
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Original file line number Diff line number Diff line change
Expand Up @@ -6,19 +6,22 @@ import compat.scalaVersionSpecific._
trait VectorInstances extends VectorInstances1 {
implicit def catsKernelStdOrderForVector[A: Order]: Order[Vector[A]] =
new VectorOrder[A]

implicit def catsKernelStdMonoidForVector[A]: Monoid[Vector[A]] =
new VectorMonoid[A]
}

private[instances] trait VectorInstances1 extends VectorInstances2 {
implicit def catsKernelStdPartialOrderForVector[A: PartialOrder]: PartialOrder[Vector[A]] =
new VectorPartialOrder[A]

implicit def catsKernelStdHashForVector[A: Hash]: Hash[Vector[A]] =
new VectorHash[A]
}

private[instances] trait VectorInstances2 {
private[instances] trait VectorInstances2 extends VectorInstances3 {
implicit def catsKernelStdPartialOrderForVector[A: PartialOrder]: PartialOrder[Vector[A]] =
new VectorPartialOrder[A]
}

private[instances] trait VectorInstances3 {
implicit def catsKernelStdEqForVector[A: Eq]: Eq[Vector[A]] =
new VectorEq[A]
}
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11 changes: 11 additions & 0 deletions tests/src/test/scala/cats/tests/ListSuite.scala
Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,17 @@ class ListSuite extends CatsSuite {
l.show should ===(l.toString)
}
}

test("the instance for `Eq[List[A]]` is not ambiguous when A has a Hash and a PartialOrder") {

import cats.kernel.{Hash, PartialOrder}

trait A
implicit def po: PartialOrder[A] = ???
implicit def ho: Hash[A] = ???

lazy val _ = implicitly[Eq[List[A]]]
}
}

final class ListInstancesSuite extends AnyFunSuiteLike {
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11 changes: 11 additions & 0 deletions tests/src/test/scala/cats/tests/QueueSuite.scala
Original file line number Diff line number Diff line change
Expand Up @@ -32,4 +32,15 @@ class QueueSuite extends CatsSuite {
Queue(1, 2, 3).show should ===("Queue(1, 2, 3)")
Queue.empty[Int].show should ===("Queue()")
}

test("the instance for `Eq[Queue[A]]` is not ambiguous when A has a Hash and a PartialOrder") {

import cats.kernel.{Hash, PartialOrder}

trait A
implicit def po: PartialOrder[A] = ???
implicit def ho: Hash[A] = ???

lazy val _ = implicitly[Eq[Queue[A]]]
}
}
11 changes: 11 additions & 0 deletions tests/src/test/scala/cats/tests/VectorSuite.scala
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,17 @@ class VectorSuite extends CatsSuite {
test("toNev on empty vector returns None") {
assert(Vector.empty[Int].toNev == None)
}

test("the instance for `Eq[Vector[A]]` is not ambiguous when A has a Hash and a PartialOrder") {

import cats.kernel.{Hash, PartialOrder}

trait A
implicit def po: PartialOrder[A] = ???
implicit def ho: Hash[A] = ???

lazy val _ = implicitly[Eq[Vector[A]]]
}
}

final class VectorInstancesSuite extends AnyFunSuiteLike {
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