Merge pull request #10404 from dotty-staging/refactor-scala-deriving

Refactor scala.deriving

Author: sjrd

library/src/scala/deriving.scala

@@ -0,0 +1,18 @@
+package scala.deriving
+
+/** Helper class to turn arrays into products */
+class ArrayProduct(val elems: Array[AnyRef]) extends Product {
+  def this(size: Int) = this(new Array[AnyRef](size))
+  def canEqual(that: Any): Boolean = true
+  def productElement(n: Int): Any = elems(n)
+  def productArity: Int = elems.length
+  override def productIterator: Iterator[Any] = elems.iterator
+  def update(n: Int, x: Any): Unit = elems(n) = x.asInstanceOf[AnyRef]
+}
+
+/** The empty product */
+object EmptyProduct extends ArrayProduct(Array.emptyObjectArray)
+
+/** Helper method to select a product element */
+def productElement[T](x: Any, idx: Int): T =
+  x.asInstanceOf[Product].productElement(idx).asInstanceOf[T]

library/src/scala/deriving/Helpers.scala

@@ -0,0 +1,52 @@
+package scala.deriving
+
+/** Mirrors allows typelevel access to enums, case classes and objects, and their sealed parents.
+ */
+sealed trait Mirror {
+
+  /** The mirrored *-type */
+  type MirroredMonoType
+
+  /** The name of the type */
+  type MirroredLabel <: String
+
+  /** The names of the product elements */
+  type MirroredElemLabels <: Tuple
+}
+
+object Mirror {
+
+  /** The Mirror for a sum type */
+  trait Sum extends Mirror { self =>
+    /** The ordinal number of the case class of `x`. For enums, `ordinal(x) == x.ordinal` */
+    def ordinal(x: MirroredMonoType): Int
+  }
+
+  /** The Mirror for a product type */
+  trait Product extends Mirror {
+
+    /** Create a new instance of type `T` with elements taken from product `p`. */
+    def fromProduct(p: scala.Product): MirroredMonoType
+  }
+
+  trait Singleton extends Product {
+    type MirroredMonoType = this.type
+    type MirroredType = this.type
+    type MirroredElemTypes = EmptyTuple
+    type MirroredElemLabels = EmptyTuple
+    def fromProduct(p: scala.Product): MirroredMonoType = this
+  }
+
+  /** A proxy for Scala 2 singletons, which do not inherit `Singleton` directly */
+  class SingletonProxy(val value: AnyRef) extends Product {
+    type MirroredMonoType = value.type
+    type MirroredType = value.type
+    type MirroredElemTypes = EmptyTuple
+    type MirroredElemLabels = EmptyTuple
+    def fromProduct(p: scala.Product): MirroredMonoType = value
+  }
+
+  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 }
+}