Invariant[Fractional]

core/src/main/scala-2.12/cats/instances/all.scala

@@ -70,3 +70,5 @@ trait AllInstancesBinCompat6 extends SortedSetInstancesBinCompat1 with SortedMap
 trait AllInstancesBinCompat7 extends SeqInstances
 
 trait AllInstancesBinCompat8 extends DeadlineInstances
+
+trait AllInstancesBinCompat9 extends InvariantInstances with InvariantInstancesBinCompat0

core/src/main/scala-2.12/cats/instances/package.scala

@@ -20,7 +20,7 @@ package object instances {
   object partialFunction extends PartialFunctionInstances
   object future extends FutureInstances
   object int extends IntInstances
-  object invariant extends InvariantMonoidalInstances with InvariantInstances
+  object invariant extends InvariantMonoidalInstances with InvariantInstances with InvariantInstancesBinCompat0
   object list extends ListInstances with ListInstancesBinCompat0
   object long extends LongInstances
   object option extends OptionInstances with OptionInstancesBinCompat0

core/src/main/scala-2.13+/cats/instances/all.scala

@@ -75,3 +75,5 @@ trait AllInstancesBinCompat7 extends SeqInstances
 trait AllInstancesBinCompat8 extends InvariantInstances
 
 trait AllInstancesBinCompat9 extends DeadlineInstances
+
+trait AllInstancesBinCompat10 extends InvariantInstancesBinCompat0

core/src/main/scala-2.13+/cats/instances/package.scala

@@ -21,7 +21,7 @@ package object instances {
   object partialFunction extends PartialFunctionInstances
   object future extends FutureInstances
   object int extends IntInstances
-  object invariant extends InvariantMonoidalInstances with InvariantInstances
+  object invariant extends InvariantMonoidalInstances with InvariantInstances with InvariantInstancesBinCompat0
   object list extends ListInstances with ListInstancesBinCompat0
   object long extends LongInstances
   object option extends OptionInstances with OptionInstancesBinCompat0

core/src/main/scala/cats/Invariant.scala

@@ -159,6 +159,8 @@ object Invariant extends ScalaVersionSpecificInvariantInstances with InvariantIn
     cats.instances.invariant.catsInvariantForNumeric
   implicit def catsInvariantForIntegral: Invariant[Integral] =
     cats.instances.invariant.catsInvariantForIntegral
+  implicit def catsInvariantForFractional: Invariant[Fractional] =
+    cats.instances.invariant.catsInvariantForFractional
 
   implicit val catsInvariantMonoid: Invariant[Monoid] = new Invariant[Monoid] {
 

core/src/main/scala/cats/instances/invariant.scala

@@ -66,3 +66,12 @@ trait InvariantInstances {
       }
   }
 }
+
+trait InvariantInstancesBinCompat0 {
+  implicit val catsInvariantForFractional: Invariant[Fractional] = new Invariant[Fractional] {
+    def imap[A, B](fa: Fractional[A])(f: A => B)(g: B => A): Fractional[B] =
+      new ScalaVersionSpecificNumeric[A, B](fa)(f)(g) with Fractional[B] {
+        override def div(x: B, y: B): B = f(fa.div(g(x), g(y)))
+      }
+  }
+}

tests/src/test/scala-2.12/cats/tests/ScalaVersionSpecific.scala

@@ -3,14 +3,17 @@ package cats.tests
 import cats.laws.discipline.{ExhaustiveCheck, MiniInt}
 import cats.laws.discipline.MiniInt._
 import cats.laws.discipline.eq._
+import cats.laws.discipline.DeprecatedEqInstances
 import cats.kernel.{Eq, Order}
+import org.scalacheck.Arbitrary
 
 trait ScalaVersionSpecificFoldableSuite
 trait ScalaVersionSpecificParallelSuite
 trait ScalaVersionSpecificRegressionSuite
 trait ScalaVersionSpecificTraverseSuite
 
 trait ScalaVersionSpecificAlgebraInvariantSuite {
+  // This version-specific instance is required since 2.12 and below do not have parseString on the Numeric class
   protected val integralForMiniInt: Integral[MiniInt] = new Integral[MiniInt] {
     def compare(x: MiniInt, y: MiniInt): Int = Order[MiniInt].compare(x, y)
     def plus(x: MiniInt, y: MiniInt): MiniInt = x + y
@@ -26,6 +29,7 @@ trait ScalaVersionSpecificAlgebraInvariantSuite {
     def rem(x: MiniInt, y: MiniInt): MiniInt = MiniInt.unsafeFromInt(x.toInt % y.toInt)
   }
 
+  // This version-specific instance is required since 2.12 and below do not have parseString on the Numeric class
   implicit protected def eqNumeric[A: Eq: ExhaustiveCheck]: Eq[Numeric[A]] = Eq.by { numeric =>
     // This allows us to catch the case where the fromInt overflows. We use the None to compare two Numeric instances,
     // verifying that when fromInt throws for one, it throws for the other.
@@ -49,4 +53,24 @@ trait ScalaVersionSpecificAlgebraInvariantSuite {
       numeric.toDouble _
     )
   }
+
+  // This version-specific instance is required since 2.12 and below do not have parseString on the Numeric class
+  implicit protected def eqFractional[A: Eq: Arbitrary]: Eq[Fractional[A]] = {
+    import DeprecatedEqInstances.catsLawsEqForFn1
+
+    Eq.by { fractional =>
+      (
+        fractional.compare _,
+        fractional.plus _,
+        fractional.minus _,
+        fractional.times _,
+        fractional.negate _,
+        fractional.fromInt _,
+        fractional.toInt _,
+        fractional.toLong _,
+        fractional.toFloat _,
+        fractional.toDouble _
+      )
+    }
+  }
 }

tests/src/test/scala-2.13+/cats/tests/ScalaVersionSpecific.scala

@@ -4,6 +4,7 @@ import cats.{Eval, Foldable, Id, Now}
 import cats.data.NonEmptyLazyList
 import cats.laws.discipline.{ExhaustiveCheck, MiniInt, NonEmptyParallelTests, ParallelTests}
 import cats.laws.discipline.arbitrary._
+import cats.laws.discipline.DeprecatedEqInstances
 import cats.syntax.either._
 import cats.syntax.foldable._
 import cats.syntax.parallel._
@@ -12,6 +13,7 @@ import cats.syntax.eq._
 import org.scalacheck.Prop._
 import cats.kernel.{Eq, Order}
 import cats.laws.discipline.eq._
+import org.scalacheck.Arbitrary
 
 trait ScalaVersionSpecificFoldableSuite { self: FoldableSuiteAdditional =>
   test("Foldable[LazyList].foldM stack safety") {
@@ -166,6 +168,7 @@ trait ScalaVersionSpecificTraverseSuite { self: TraverseSuiteAdditional =>
 
 trait ScalaVersionSpecificAlgebraInvariantSuite {
 
+  // This version-specific instance is required since 2.12 and below do not have parseString on the Numeric class
   protected val integralForMiniInt: Integral[MiniInt] = new Integral[MiniInt] {
     def compare(x: MiniInt, y: MiniInt): Int = Order[MiniInt].compare(x, y)
     def plus(x: MiniInt, y: MiniInt): MiniInt = x + y
@@ -182,6 +185,7 @@ trait ScalaVersionSpecificAlgebraInvariantSuite {
     def parseString(str: String): Option[MiniInt] = Integral[Int].parseString(str).flatMap(MiniInt.fromInt)
   }
 
+  // This version-specific instance is required since 2.12 and below do not have parseString on the Numeric class
   implicit protected def eqNumeric[A: Eq: ExhaustiveCheck]: Eq[Numeric[A]] = Eq.by { numeric =>
     // This allows us to catch the case where the fromInt overflows. We use the None to compare two Numeric instances,
     // verifying that when fromInt throws for one, it throws for the other.
@@ -212,6 +216,34 @@ trait ScalaVersionSpecificAlgebraInvariantSuite {
     )
   }
 
+  // This version-specific instance is required since 2.12 and below do not have parseString on the Numeric class
+  implicit protected def eqFractional[A: Eq: Arbitrary]: Eq[Fractional[A]] = {
+    // This deprecated instance is required since there is not `ExhaustiveCheck` for any types for which a `Fractional`
+    // can easily be defined
+    import DeprecatedEqInstances.catsLawsEqForFn1
+
+    Eq.by { fractional =>
+      val parseFloatStrings: Option[Double] => Option[A] = {
+        case Some(f) => fractional.parseString(f.toString)
+        case None    => fractional.parseString("invalid") // Use this to test parsing of non-numeric strings
+      }
+
+      (
+        fractional.compare _,
+        fractional.plus _,
+        fractional.minus _,
+        fractional.times _,
+        fractional.negate _,
+        fractional.fromInt _,
+        fractional.toInt _,
+        fractional.toLong _,
+        fractional.toFloat _,
+        fractional.toDouble _,
+        parseFloatStrings
+      )
+    }
+  }
+
 }
 
 class TraverseLazyListSuite extends TraverseSuite[LazyList]("LazyList")

tests/src/test/scala/cats/tests/AlgebraInvariantSuite.scala

@@ -160,6 +160,9 @@ class AlgebraInvariantSuite extends CatsSuite with ScalaVersionSpecificAlgebraIn
 
   implicit private val arbNumericMiniInt: Arbitrary[Numeric[MiniInt]] = Arbitrary(Gen.const(integralForMiniInt))
   implicit private val arbIntegralMiniInt: Arbitrary[Integral[MiniInt]] = Arbitrary(Gen.const(integralForMiniInt))
+  implicit private val arbFractionalFloat: Arbitrary[Fractional[Float]] = Arbitrary(
+    Gen.const(implicitly[Fractional[Float]])
+  )
 
   implicit protected def eqIntegral[A: Eq: ExhaustiveCheck]: Eq[Integral[A]] = {
     def makeDivisionOpSafe(unsafeF: (A, A) => A): (A, A) => Option[A] =
@@ -196,6 +199,7 @@ class AlgebraInvariantSuite extends CatsSuite with ScalaVersionSpecificAlgebraIn
 
   checkAll("Invariant[Numeric]", InvariantTests[Numeric].invariant[MiniInt, Boolean, Boolean])
   checkAll("Invariant[Integral]", InvariantTests[Integral].invariant[MiniInt, Boolean, Boolean])
+  checkAll("Invariant[Fractional]", InvariantTests[Fractional].invariant[Float, Boolean, Boolean])
 
   {
     val S: Semigroup[Int] = Semigroup[Int].imap(identity)(identity)