Reimplementing enum macros for Scala 3. Based on pureconfig's which a…

…re more lightweight. (#207)
theiterators · May 17, 2022 · 57acb2a · 57acb2a
1 parent d610bbe
commit 57acb2a
Showing 1 changed file with 25 additions and 12 deletions.
diff --git a/macro-utils/src/main/scala-3/pl/iterators/kebs/macros/enums/EnumEntryMacros.scala b/macro-utils/src/main/scala-3/pl/iterators/kebs/macros/enums/EnumEntryMacros.scala
@@ -1,6 +1,9 @@
 package pl.iterators.kebs.macros.enums
 
 import scala.quoted._
+import scala.compiletime.{constValue, erasedValue, error, summonInline}
+import scala.deriving.Mirror
+import scala.reflect.{ClassTag, Enum}
 
 trait EnumLike[T] {
   def values: Array[T]
@@ -11,19 +14,29 @@ trait EnumLike[T] {
 class EnumOf[E](val `enum`: EnumLike[E])
 
 object EnumOf {
-  inline given [E]: EnumOf[E] = ${EnumOf.impl[E]()}
+  inline given [E <: Enum](using m: Mirror.SumOf[E], ct: ClassTag[E]): EnumOf[E] = {
+    val enumValues = summonCases[m.MirroredElemTypes, E]
+    EnumOf[E](new EnumLike[E] {
+      override def values: Array[E] = enumValues.toArray
+      override def valueOf(name: String): E = enumValues.find(_.toString == name).getOrElse(throw new IllegalArgumentException(s"enum case not found: $name"))
+      override def fromOrdinal(ordinal: Int): E = enumValues.lift(ordinal).getOrElse(throw new NoSuchElementException(ordinal.toString))
+    })
+  }
 
-  private def impl[T]()(using Quotes, Type[T]): Expr[EnumOf[T]] = {
-    import quotes.reflect._
-    val companion = Ref(TypeRepr.of[T].typeSymbol.companionModule)
-    '{
-      new EnumOf(
-        new EnumLike[T] {
-          def values: Array[T] = ${Select.unique(companion, "values").asExprOf[Array[T]]}
-          def valueOf(name: String): T = ${Apply(Select.unique(companion, "valueOf"), List('{name}.asTerm)).asExprOf[T]}
-          def fromOrdinal(ordinal: Int): T = ${Apply(Select.unique(companion, "fromOrdinal"), List('{ordinal}.asTerm)).asExprOf[T]}
-        }
-      )
+  inline private def widen[A, B](a: A): A & B =
+    inline a match {
+      case b: B => b
     }
+
+  inline private def summonCases[T <: Tuple, A]: List[A] =
+    inline erasedValue[T] match {
+    case _: (h *: t) =>
+      (inline summonInline[Mirror.Of[h]] match {
+        case m: Mirror.Singleton =>
+          widen[m.MirroredMonoType, A](m.fromProduct(EmptyTuple)) :: summonCases[t, A]
+        case x => error("Enums cannot include parameterized cases.")
+      })
+
+    case _: EmptyTuple => Nil
   }
 }