Merge pull request #9209 from dotty-staging/add-summonAll-and-constValueTuple

Add summonAll and constValueTuple

Author: anatoliykmetyuk

library/src/scala/Tuple.scala

@@ -143,6 +143,18 @@ object Tuple {
     }
   }
 
+  /**
+   * Use this type to widen a self-type to a tuple. E.g.
+   * ```
+   * val x: (1, 3) = (1, 3)
+   * val y: Widen[x.type] = x
+   * ```
+   */
+  type Widen[Tup <: Tuple] <: Tuple = Tup match {
+    case EmptyTuple => EmptyTuple
+    case h *: t => h *: t
+  }
+
   /** Given two tuples, `A1 *: ... *: An * At` and `B1 *: ... *: Bn *: Bt`
    *  where at least one of `At` or `Bt` is `EmptyTuple` or `Tuple`,
    *  returns the tuple type `(A1, B1) *: ... *: (An, Bn) *: Ct`

library/src/scala/compiletime/package.scala

@@ -4,6 +4,16 @@ import scala.quoted._
 
 package object compiletime {
 
+  /** Use this method when you have a type, do not have a value for it but want to
+   *  pattern match on it. For example, given a type `Tup <: Tuple`, one can
+   *  pattern-match on it as follows:
+   *  ```
+   *  erasedValue[Tup] match {
+   *    case _: EmptyTuple => ...
+   *    case _: h *: t => ...
+   *  }
+   *  ```
+   */
   erased def erasedValue[T]: T = ???
 
   /** The error method is used to produce user-defined compile errors during inline expansion.
@@ -38,10 +48,29 @@ package object compiletime {
   transparent inline def (inline self: StringContext) code (inline args: Any*): String =
     ${ dotty.internal.CompileTimeMacros.codeExpr('self, 'args) }
 
+  /** Same as `constValue` but returns a `None` if a constant value
+   *  cannot be constructed from the provided type. Otherwise returns
+   *  that value wrapped in `Some`.
+   */
   inline def constValueOpt[T]: Option[T] = ???
 
+  /** Given a constant, singleton type `T`, convert it to a value
+   *  of the same singleton type. For example: `assert(constValue[1] == 1)`.
+   */
   inline def constValue[T]: T = ???
 
+  /** Given a tuple type `(X1, ..., Xn)`, returns a tuple value
+   *  `(constValue[X1], ..., constValue[Xn])`.
+   */
+  inline def constValueTuple[T <: Tuple]: Tuple.Widen[T]=
+    val res =
+      inline erasedValue[T] match
+        case _: EmptyTuple => EmptyTuple
+        case _: (t *: ts) => constValue[t] *: constValueTuple[ts]
+      end match
+    res.asInstanceOf[Tuple.Widen[T]]
+  end constValueTuple
+
   /** Summons first given matching one of the listed cases. E.g. in
    *
    *      given B { ... }
@@ -68,6 +97,20 @@ package object compiletime {
     case t: T => t
   }
 
+  /** Given a tuple T, summons each of its member types and returns them in
+   *  a Tuple.
+   *
+   *  @tparam T the tuple containing the types of the values to be summoned
+   *  @return the given values typed as elements of the tuple
+   */
+  inline def summonAll[T <: Tuple]: Tuple.Widen[T] =
+    val res =
+      inline erasedValue[T] match
+        case _: EmptyTuple => EmptyTuple
+        case _: (t *: ts) => summonInline[t] *: summonAll[ts]
+      end match
+    res.asInstanceOf[Tuple.Widen[T]]
+  end summonAll
 
   /** Succesor of a natural number where zero is the type 0 and successors are reduced as if the definition was
    *

tests/run/constValueTuple.check

@@ -0,0 +1 @@
+(foo,bar,10,2.5)

tests/run/constValueTuple.scala

@@ -0,0 +1,4 @@
+import compiletime.constValueTuple
+
+@main def Test =
+  println(constValueTuple["foo" *: "bar" *: 10 *: 2.5 *: EmptyTuple])

tests/run/summonAll.check

@@ -0,0 +1 @@
+(10,foo,1.2)

tests/run/summonAll.scala

@@ -0,0 +1,7 @@
+import compiletime.summonAll
+
+@main def Test =
+  given as Int = 10
+  given as String = "foo"
+  given as Double = 1.2
+  println(summonAll[Int *: String *: Double *: EmptyTuple])