Derive Contravariant and Invariant (#346)

core/src/main/scala-3/cats/derived/all.scala

@@ -3,17 +3,20 @@ package cats.derived
 object all extends
   CommutativeMonoidDerivation,
   CommutativeSemigroupDerivation,
+  ContravariantDerivation,
   EmptyDerivation,
   EmptyKDerivation,
   EqDerivation,
   FoldableDerivation,
   FunctorDerivation,
   HashDerivation,
+  InvariantDerivation,
   MonoidDerivation,
   MonoidKDerivation,
   OrderDerivation,
   PartialOrderDerivation,
   SemigroupDerivation,
   SemigroupKDerivation,
   ShowDerivation,
-  TraverseDerivation
+  TraverseDerivation,
+  Instances

core/src/main/scala-3/cats/derived/contravariant.scala

@@ -0,0 +1,18 @@
+package cats.derived
+
+import cats.Contravariant
+import shapeless3.deriving.K1
+
+object contravariant extends ContravariantDerivation, Instances
+
+trait GenericContravariant[T[x[_]] <: Contravariant[x], F[_]](using inst: K1.Instances[T, F])
+  extends Contravariant[F]:
+
+  def contramap[A, B](fa: F[A])(f: B => A): F[B] = inst.map(fa)(
+    [t[_]] => (contra: T[t], t0: t[A]) => contra.contramap(t0)(f)
+  )
+
+trait ContravariantDerivation:
+  extension (F: Contravariant.type)
+    inline def derived[F[_]](using gen: K1.Generic[F]): Contravariant[F] =
+      new GenericContravariant[Contravariant, F]{}

core/src/main/scala-3/cats/derived/foldable.scala

@@ -3,7 +3,7 @@ package cats.derived
 import cats.{Eval, Foldable}
 import shapeless3.deriving.{Const, Continue, K1}
 
-object foldable extends FoldableDerivation
+object foldable extends FoldableDerivation, Instances
 
 trait ProductFoldable[T[x[_]] <: Foldable[x], F[_]](using inst: K1.ProductInstances[T, F])
     extends Foldable[F]:
@@ -41,7 +41,3 @@ trait FoldableDerivation:
 
   given coproductFoldable[F[_]](using inst: => K1.CoproductInstances[Foldable, F]): Foldable[F] =
     new CoproductFoldable[Foldable, F]{}
-
-  given [X]: Foldable[Const[X]] with
-    def foldLeft[A, B](fa: X, b: B)(f: (B, A) => B): B = b
-    def foldRight[A, B](fa: X, lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] = lb

core/src/main/scala-3/cats/derived/functor.scala

@@ -3,7 +3,7 @@ package cats.derived
 import cats.Functor
 import shapeless3.deriving.{Const, K1}
 
-object functor extends FunctorDerivation
+object functor extends FunctorDerivation, Instances
 
 trait GenericFunctor[T[x[_]] <: Functor[x], F[_]](using inst: K1.Instances[T, F])
     extends Functor[F]:
@@ -17,6 +17,3 @@ trait FunctorDerivation:
   extension (F: Functor.type)
     inline def derived[F[_]](using gen: K1.Generic[F]): Functor[F] =
       new GenericFunctor[Functor, F]{}
-
-  given [X]: Functor[Const[X]] with
-    def map[A, B](fa: X)(f: A => B): X = fa

core/src/main/scala-3/cats/derived/instances.scala

@@ -0,0 +1,29 @@
+package cats.derived
+
+import cats.*
+import shapeless3.deriving.Const
+
+private[derived] trait Instances extends Instances1:
+
+  given [X](using X: Monoid[X]): MonoidK[Const[X]] with
+    def empty[A]: Const[X][A] = X.empty
+
+    def combineK[A](x: Const[X][A], y: Const[X][A]): Const[X][A] =
+      X.combine(x, y)
+
+  given [X]: Traverse[Const[X]] with Contravariant[Const[X]] with
+    override def map[A, B](fa: Const[X][A])(f: A => B): Const[X][B] = fa
+
+    def contramap[A, B](fa: X)(f: B => A): X = fa
+
+    def foldLeft[A, B](fa: Const[X][A], b: B)(f: (B, A) => B): B = b
+
+    def foldRight[A, B](fa: Const[X][A], lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] = lb
+
+    def traverse[G[_]: Applicative, A, B](fa: Const[X][A])(f: A => G[B]): G[Const[X][B]] =
+      Applicative[G].pure(fa)
+
+private[derived] trait Instances1:
+  given [X](using X: Semigroup[X]): SemigroupK[Const[X]] with
+    def combineK[A](x: Const[X][A], y: Const[X][A]): Const[X][A] =
+      X.combine(x, y)

core/src/main/scala-3/cats/derived/invariant.scala

@@ -0,0 +1,17 @@
+package cats.derived
+
+import cats.Invariant
+import shapeless3.deriving.K1
+
+object invariant extends InvariantDerivation, Instances
+
+trait GenericInvariant[T[x[_]] <: Invariant[x], F[_]](using inst: K1.Instances[T, F])
+  extends Invariant[F]:
+    def imap[A, B](fa: F[A])(f: A => B)(g: B => A): F[B] = inst.map(fa)(
+      [t[_]] => (inv: T[t], t0: t[A]) => inv.imap(t0)(f)(g)
+    )
+
+trait InvariantDerivation:
+  extension (F: Invariant.type)
+    inline def derived[F[_]](using gen: K1.Generic[F]): Invariant[F] =
+      new GenericInvariant[Invariant, F]{}

core/src/main/scala-3/cats/derived/monoidk.scala

@@ -3,7 +3,7 @@ package cats.derived
 import cats.{Monoid, MonoidK}
 import shapeless3.deriving.{Const, K1}
 
-object monoidk extends MonoidKDerivation
+object monoidk extends MonoidKDerivation, Instances
 
 trait ProductMonoidK[T[x[_]] <: MonoidK[x], F[_]](using inst: K1.ProductInstances[T, F])
   extends ProductSemigroupK[T, F], MonoidK[F]:
@@ -12,7 +12,3 @@ trait ProductMonoidK[T[x[_]] <: MonoidK[x], F[_]](using inst: K1.ProductInstance
 trait MonoidKDerivation:
   extension (F: MonoidK.type)
     inline def derived[F[_]](using gen: K1.Generic[F]): MonoidK[F] = ???
-
-  given [X](using X: Monoid[X]): MonoidK[Const[X]] with
-    def empty[A]: X = X.empty
-    def combineK[A](x: X, y: X): X = X.combine(x, y)

core/src/main/scala-3/cats/derived/semigroupk.scala

@@ -3,7 +3,7 @@ package cats.derived
 import cats.{Semigroup, SemigroupK}
 import shapeless3.deriving.{Const, K1}
 
-object semigroupk extends SemigroupKDerivation
+object semigroupk extends SemigroupKDerivation, Instances
 
 trait ProductSemigroupK[T[x[_]] <: SemigroupK[x], F[_]](using inst: K1.ProductInstances[T, F])
   extends SemigroupK[F]:
@@ -15,7 +15,3 @@ trait SemigroupKDerivation:
   extension (F: SemigroupK.type)
     inline def derived[F[_]](using gen: K1.ProductGeneric[F]): SemigroupK[F] =
       new ProductSemigroupK[SemigroupK, F]{}
-
-  given [X](using X: Semigroup[X]): SemigroupK[Const[X]] with
-    def combineK[A](x: X, y: X): X =
-      X.combine(x, y)

core/src/main/scala-3/cats/derived/traverse.scala

@@ -3,7 +3,7 @@ package cats.derived
 import cats.{Applicative, Eval, Traverse}
 import shapeless3.deriving.{Const, Continue, K1}
 
-object traverse extends TraverseDerivation
+object traverse extends TraverseDerivation, Instances
 
 trait ProductTraverse[T[x[_]] <: Traverse[x], F[_]](using inst: K1.ProductInstances[T, F])
     extends GenericFunctor[T, F], ProductFoldable[T, F], Traverse[F]:
@@ -31,9 +31,3 @@ trait TraverseDerivation:
 
   given coproductTraverse[F[_]](using inst: => K1.CoproductInstances[Traverse, F]): Traverse[F] =
     new CoproductTraverse[Traverse, F]{}
-
-  given [X]: Traverse[Const[X]] with
-    override def map[A, B](fa: X)(f: A => B): X = fa
-    def foldLeft[A, B](fa: X, b: B)(f: (B, A) => B): B = b
-    def foldRight[A, B](fa: X, lb: Eval[B])(f: (A, Eval[B]) => Eval[B]): Eval[B] = lb
-    def traverse[G[_]: Applicative, A, B](fa: X)(f: A => G[B]): G[X] = Applicative[G].pure(fa)

core/src/test/scala-3/cats/derived/ContravariantTests.scala

@@ -0,0 +1,11 @@
+package cats.derived
+
+import cats.Contravariant
+import cats.derived.all._
+import cats.derived.all.given
+
+class ContravariantTests {
+
+  case class Foo[A](f: A => String) derives Contravariant
+
+}

core/src/test/scala-3/cats/derived/InvariantTests.scala

@@ -0,0 +1,11 @@
+package cats.derived
+
+import cats.Invariant
+import cats.derived.all._
+import cats.derived.all.given
+
+class InvariantTests {
+
+  case class Foo[A](bar: String, baz: Option[A]) derives Invariant
+
+}