Add String to Liftable expressions and abstract over all primitives

Author: nicolasstucki

compiler/src/dotty/tools/dotc/quoted/PickledQuotes.scala

@@ -27,7 +27,7 @@ object PickledQuotes {
   /** Transform the expression into it's fully spliced Tree */
   def quotedToTree(expr: quoted.Quoted)(implicit ctx: Context): Tree = expr match {
     case expr: quoted.TastyQuoted => unpickleQuote(expr)
-    case expr: quoted.ValueExpr[_] => Literal(Constant(expr.value))
+    case expr: quoted.Liftable.PrimitiveExpr[_] => Literal(Constant(expr.value))
     case expr: RawQuoted => expr.tree
   }
 

library/src/scala/quoted/Liftable.scala

@@ -13,6 +13,13 @@ abstract class Liftable[T] {
  *  gives an alternative implementation using just the basic staging system.
  */
 object Liftable {
+
+  sealed abstract class PrimitiveExpr[T] extends Expr[T] {
+    def value: T
+  }
+
+  private class ValueExpr[T <: AnyVal](val value: T) extends PrimitiveExpr[T]
+
   implicit def BooleanIsLiftable: Liftable[Boolean] = (x: Boolean) => new ValueExpr(x)
   implicit def ByteLiftable: Liftable[Byte] = (x: Byte) => new ValueExpr(x)
   implicit def CharIsLiftable: Liftable[Char] = (x: Char) => new ValueExpr(x)
@@ -21,4 +28,8 @@ object Liftable {
   implicit def LongIsLiftable: Liftable[Long] = (x: Long) => new ValueExpr(x)
   implicit def FloatIsLiftable: Liftable[Float] = (x: Float) => new ValueExpr(x)
   implicit def DoubleIsLiftable: Liftable[Double] = (x: Double) => new ValueExpr(x)
+
+  private class StringExpr(val value: String) extends PrimitiveExpr[String]
+
+  implicit def StringIsLiftable: Liftable[String] = (x: String) => new StringExpr(x)
 }

library/src/scala/quoted/ValueExpr.scala

@@ -32,6 +32,7 @@ object Test {
   (1L: Expr[Long])
   (1.0f: Expr[Float])
   (1.0: Expr[Double])
+  ("abc": Expr[String])
 
   val xs: Expr[List[Int]] = 1 :: 2 :: 3 :: Nil
 }