Change nested pairs to HList conversions for consistency

To be more consistent with nested `Either` to `Coproduct` conversions.
milessabin · Mar 18, 2020 · 3ca0948 · 3ca0948
1 parent 506e397
commit 3ca0948
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Showing 4 changed files with 30 additions and 26 deletions.
diff --git a/core/src/main/scala/shapeless/ops/hlists.scala b/core/src/main/scala/shapeless/ops/hlists.scala
@@ -3074,26 +3074,26 @@ object hlist {
    *
    * @author Michael Zuber
    */
-  sealed trait ToHList[-T] {
+  sealed trait ProductToHList[-T] extends Serializable {
     type Out <: HList
     def apply(t: T): Out
   }
 
-  object ToHList {
-    def apply[P](implicit ev: ToHList[P]): ToHList[P] = ev
+  object ProductToHList {
+    def apply[P](implicit ev: ProductToHList[P]): ProductToHList[P] = ev
 
-    type Aux[P, HL <: HList] = ToHList[P] { type Out = HL }
+    type Aux[P, HL <: HList] = ProductToHList[P] { type Out = HL }
 
-    implicit def hconsToHList[H, TH, TT, HL <: HList](implicit
-      ev: ToHList.Aux[Product2[TH, TT], HL]
-    ): ToHList.Aux[Product2[H, Product2[TH, TT]], H :: HL] = new ToHList[Product2[H, Product2[TH, TT]]] {
+    implicit def pairToHCons[H, T, HL <: HList](
+      implicit ev: ProductToHList.Aux[T, HL]
+    ): ProductToHList.Aux[Product2[H, T], H :: HL] = new ProductToHList[Product2[H, T]] {
       type Out = H :: HL
-      def apply(p: Product2[H, Product2[TH, TT]]): Out = p._1 :: ev(p._2)
+      def apply(p: Product2[H, T]): Out = p._1 :: ev(p._2)
     }
 
-    implicit def hnilToHList[H]: ToHList.Aux[Product2[H, Unit], H :: HNil] = new ToHList[Product2[H, Unit]] {
-      type Out = H :: HNil
-      def apply(p: Product2[H, Unit]): Out = p._1 :: HNil
+    implicit val unitToHNil: ProductToHList.Aux[Unit, HNil] = new ProductToHList[Unit] {
+      type Out = HNil
+      def apply(p: Unit): Out = HNil
     }
   }
 
@@ -3102,23 +3102,23 @@ object hlist {
    *
    * @author Michael Zuber
    */
-  sealed trait HListToProduct[HL <: HList] extends DepFn1[HL] { type Out <: Product }
+  sealed trait HListToProduct[HL <: HList] extends DepFn1[HL] with Serializable
 
   object HListToProduct {
     def apply[HL <: HList](implicit ev: HListToProduct[HL]): HListToProduct[HL] = ev
 
-    type Aux[HL <: HList, P <: Product] = HListToProduct[HL] { type Out = P }
+    type Aux[HL <: HList, P] = HListToProduct[HL] { type Out = P }
 
-    implicit def hnilToProduct[H]: HListToProduct.Aux[H :: HNil, Product2[H, Unit]] = new HListToProduct[H :: HNil] {
-      type Out = Product2[H, Unit]
-      def apply(hl: H :: HNil): Out = (hl.head, ())
+    implicit val hnilToUnit: HListToProduct.Aux[HNil, Unit] = new HListToProduct[HNil] {
+      type Out = Unit
+      def apply(hl: HNil): Out = ()
     }
 
-    implicit def hconsHListToProduct[H, T <: HList, TP <: Product](implicit
-      ev: HListToProduct.Aux[T, TP]
-    ): HListToProduct.Aux[H :: T, Product2[H, TP]] = new HListToProduct[H :: T] {
-      type Out = Product2[H, TP]
-      def apply(hl: H :: T) = (hl.head, ev(hl.tail))
+    implicit def hconsToPair[H, T <: HList, TP](
+      implicit ev: HListToProduct.Aux[T, TP]
+    ): HListToProduct.Aux[H :: T, (H, TP)] = new HListToProduct[H :: T] {
+      type Out = (H, TP)
+      def apply(hl: H :: T): Out = (hl.head, ev(hl.tail))
     }
   }
 }
diff --git a/core/src/main/scala/shapeless/syntax/hlists.scala b/core/src/main/scala/shapeless/syntax/hlists.scala
@@ -748,5 +748,5 @@ final class HListOps[L <: HList](l : L) extends Serializable {
   /**
    * Converts this `HList` into a nested pair
    */
-  def nestedProduct(implicit hListToProduct: HListToProduct[L]): hListToProduct.Out = hListToProduct(l)
+  def toProduct(implicit hListToProduct: HListToProduct[L]): hListToProduct.Out = hListToProduct(l)
 }
diff --git a/core/src/main/scala/shapeless/syntax/std/tuples.scala b/core/src/main/scala/shapeless/syntax/std/tuples.scala
@@ -18,6 +18,8 @@ package shapeless
 package syntax
 package std
 
+import shapeless.ops.hlist.ProductToHList
+
 trait LowPriorityTuple {
   implicit def productTupleOps[P <: Product](p: P): TupleOps[P] = new TupleOps(p)
 }
@@ -524,5 +526,5 @@ final class TupleOps[T](t: T) extends Serializable {
   /**
    * Converts this nested `Product` into an `HList`
    */
-  def toHList(implicit toHList: ops.hlist.ToHList[T]): toHList.Out = toHList(t)
+  def toHList(implicit productToHList: ProductToHList[T]): productToHList.Out = productToHList(t)
 }
diff --git a/core/src/test/scala/shapeless/hlist.scala b/core/src/test/scala/shapeless/hlist.scala
@@ -3490,9 +3490,11 @@ class HListTests {
     val p = (2, ("abc", (true, (3.0, ()))))
 
     import syntax.std.tuple._
-    assertEquals(isbd.nestedProduct, p)
+    assertEquals(isbd.toProduct, p)
     assertEquals(p.toHList, isbd)
-    assertEquals(isbd.nestedProduct.toHList, isbd)
-    assertEquals(p.toHList.nestedProduct, p)
+    assertEquals(isbd.toProduct.toHList, isbd)
+    assertEquals(p.toHList.toProduct, p)
+    assertEquals((), (HNil: HNil).toProduct)
+    assertEquals(HNil, ().toHList)
   }
 }