Strict derivation for Hash

typelevel · Dec 17, 2023 · 122933d · 122933d
1 parent 036b65e
commit 122933d
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Showing 4 changed files with 31 additions and 1 deletion.
diff --git a/core/src/main/scala-3/cats/derived/DerivedEq.scala b/core/src/main/scala-3/cats/derived/DerivedEq.scala
@@ -13,6 +13,7 @@ Make sure that A satisfies one of the following conditions:
 type DerivedEq[A] = Derived[Eq[A]]
 object DerivedEq:
   type Or[A] = Derived.Or[Eq[A]]
+
   inline def apply[A]: Eq[A] =
     import DerivedEq.given
     summonInline[DerivedEq[A]].instance
@@ -42,5 +43,5 @@ object DerivedEq:
       [t] => (eqt: F[t], x: t, y: t) => eqt.eqv(x, y)
 
   object Strict:
-    given product[A](using inst: => K0.ProductInstances[Eq, A]): DerivedEq[A] =
+    given product[A](using => K0.ProductInstances[Eq, A]): DerivedEq[A] =
       new Product[Eq, A] {}
diff --git a/core/src/main/scala-3/cats/derived/DerivedHash.scala b/core/src/main/scala-3/cats/derived/DerivedHash.scala
@@ -14,10 +14,16 @@ Make sure that A satisfies one of the following conditions:
 type DerivedHash[A] = Derived[Hash[A]]
 object DerivedHash:
   type Or[A] = Derived.Or[Hash[A]]
+
   inline def apply[A]: Hash[A] =
     import DerivedHash.given
     summonInline[DerivedHash[A]].instance
 
+  inline def strict[A]: Hash[A] =
+    import DerivedHash.given
+    import Strict.product
+    summonInline[DerivedHash[A]].instance
+
   // These instances support singleton types unlike the instances in Cats' kernel.
   given boolean[A <: Boolean]: DerivedHash[A] = Hash.fromUniversalHashCode
   given byte[A <: Byte]: DerivedHash[A] = Hash.fromUniversalHashCode
@@ -57,3 +63,7 @@ object DerivedHash:
 
     final override def hash(x: A): Int =
       inst.fold[Int](x)([t] => (h: F[t], x: t) => h.hash(x))
+
+  object Strict:
+    given product[A <: scala.Product](using => K0.ProductInstances[Hash, A]): DerivedHash[A] =
+      new Product[Hash, A] {}
diff --git a/core/src/main/scala-3/cats/derived/package.scala b/core/src/main/scala-3/cats/derived/package.scala
@@ -59,9 +59,11 @@ object semiauto:
 
 object strict:
   extension (x: Eq.type) inline def derived[A]: Eq[A] = DerivedEq.strict[A]
+  extension (x: Hash.type) inline def derived[A]: Hash[A] = DerivedHash.strict[A]
 
   object semiauto:
     inline def eq[A]: Eq[A] = DerivedEq.strict[A]
+    inline def hash[A]: Hash[A] = DerivedHash.strict[A]
 
 object auto:
   object eq:

diff --git a/core/src/test/scala-3/cats/derived/HashSuite.scala b/core/src/test/scala-3/cats/derived/HashSuite.scala
@@ -30,6 +30,11 @@ class HashSuite extends KittensSuite:
     import semiInstances.given
     validate("semiauto.hash")
 
+  locally:
+    import strictInstances.given
+    validate("strict.semiauto.hash")
+    testNoInstance("strict.semiauto.hash", "Top")
+
   locally:
     import derivedInstances.*
     val instance = "derived.hash"
@@ -58,6 +63,18 @@ object HashSuite:
     given Hash[EnumK0] = semiauto.hash
     given Hash[Singletons[Int]] = semiauto.hash
 
+  object strictInstances:
+    given Hash[IList[Int]] = strict.semiauto.hash
+    given Hash[Inner] = strict.semiauto.hash
+    given Hash[Outer] = strict.semiauto.hash
+    given Hash[Interleaved[Int]] = strict.semiauto.hash
+    given Hash[Tree[Int]] = strict.semiauto.hash
+    given Hash[Recursive] = strict.semiauto.hash
+    given Hash[EnumK0] = strict.semiauto.hash
+    given Hash[Singletons[Int]] =
+      given [A <: Singleton: ValueOf]: Hash[A] = Hash.fromUniversalHashCode
+      strict.semiauto.hash
+
   object derivedInstances:
     case class IList[A](x: ADTs.IList[A]) derives Hash
     case class Inner(x: ADTs.Inner) derives Hash