Add typed versions of Mirror.ProductOf#fromProduct

Author: mpilquist

library/src/scala/deriving/Mirror.scala

@@ -49,4 +49,13 @@ object Mirror {
   type Of[T] = Mirror { type MirroredType = T; type MirroredMonoType = T ; type MirroredElemTypes <: Tuple }
   type ProductOf[T] = Mirror.Product { type MirroredType = T; type MirroredMonoType = T ; type MirroredElemTypes <: Tuple }
   type SumOf[T] = Mirror.Sum { type MirroredType = T; type MirroredMonoType = T; type MirroredElemTypes <: Tuple }
+
+  extension [T](p: ProductOf[T])
+    /** Create a new instance of type `T` with elements taken from product `a`. */
+    def fromProductTyped[A <: scala.Product](a: A)(using m: ProductOf[A], ev: p.MirroredElemTypes =:= m.MirroredElemTypes): T =
+      p.fromProduct(a)
+
+    /** Create a new instance of type `T` with elements taken from tuple `t`. */
+    def fromTuple(t: p.MirroredElemTypes): T =
+      p.fromProduct(t)
 }

tests/neg/deriving.scala

@@ -1,6 +1,6 @@
-import reflect.Generic
+import deriving.MirrorOf
 
-sealed trait A derives Generic // error: cannot take shape, it has anonymous or inaccessible subclasses
+sealed trait A
 
 object A {
   def f() = {
@@ -9,17 +9,28 @@ object A {
   }
 }
 
-sealed trait B derives Generic // error: cannot take shape, its subclass class D is not a case class
+def aMirror = summon[Mirror.Of[A]] // error: cannot take shape, it has anonymous or inaccessible subclasses
+
+sealed trait B
 
 class D(x: Int, y: String) extends B
 
+def bMirror = summon[Mirror.Of[B]] // error: cannot take shape, its subclass class D is not a case class
 
-class E derives Generic // error: cannot take shape, it is neither sealed nor a case class
+class E
+def eMirror = summon[Mirror.Of[E]] // error: cannot take shape, it is neither sealed nor a case class
 
-sealed trait F derives Generic // error: cannot take shape, it has anonymous or inaccessible subclasses
+sealed trait F
+def fMirror = summon[Mirror.Of[F]] // error: cannot take shape, it has anonymous or inaccessible subclasses
 
 object G {
   def f() = {
     case class H() extends F
   }
 }
+
+case class I(x: Int, y: String)
+object I:
+  def f = summon[deriving.Mirror.ProductOf[I]].fromProductTyped((1, 2)) // error
+  def g = summon[deriving.Mirror.ProductOf[I]].fromTuple((1, 2)) // error
+

tests/run/deriving.scala

@@ -13,6 +13,8 @@ object Test extends App {
   case class AA[X >: Null <: AnyRef](x: X, y: X, z: String)
 
   println(summon[Mirror.ProductOf[A]].fromProduct(A(1, 2)))
+  summon[Mirror.ProductOf[A]].fromProductTyped(A(1, 2))
+  summon[Mirror.ProductOf[A]].fromTuple((1, 2))
   assert(summon[Mirror.SumOf[T]].ordinal(A(1, 2)) == 0)
   assert(summon[Mirror.Sum { type MirroredType = T }].ordinal(B) == 1)
   summon[Mirror.Of[A]] match {