Implement Tuple.FlatMap

closes #13163

Author: KacperFKorban

library/src/scala/Tuple.scala

@@ -54,6 +54,12 @@ sealed trait Tuple extends Product {
   inline def map[F[_]](f: [t] => t => F[t]): Map[this.type, F] =
     runtime.Tuples.map(this, f).asInstanceOf[Map[this.type, F]]
 
+  /** Called on a tuple `(a1, ..., an)`, returns a new tuple `f(a1) ++ ... ++ f(an)`.
+   *  The result is typed as `Concat[F[A1], ...Concat[F[An], EmptyTuple]...])` if the tuple type is fully known.
+   */
+  inline def flatMap[F[_] <: Tuple](f: [t] => t => F[t]): FlatMap[this.type, F] =
+    runtime.Tuples.flatMap(this, f).asInstanceOf[FlatMap[this.type, F]]
+
   /** Given a tuple `(a1, ..., am)`, returns the tuple `(a1, ..., an)` consisting
    *  of its first n elements.
    */

library/src/scala/runtime/Tuples.scala

@@ -388,6 +388,11 @@ object Tuples {
     case _ => fromIArray(self.productIterator.map(f(_).asInstanceOf[Object]).toArray.asInstanceOf[IArray[Object]]) // TODO use toIArray
   }
 
+  def flatMap[F[_] <: Tuple](self: Tuple, f: [t] => t => F[t]): Tuple = self match {
+    case EmptyTuple => self
+    case _ => fromIArray(self.toIArray.flatMap(f(_).toIArray))
+  }
+
   def take(self: Tuple, n: Int): Tuple = {
     if (n < 0) throw new IndexOutOfBoundsException(n.toString)
     val selfSize: Int = self.size

tests/run/TupleFlatMap.check

@@ -0,0 +1,4 @@
+()
+(1,1,2,2,x,x,d,d)
+()
+(1,1!,x,x!)

tests/run/TupleFlatMap.scala

@@ -0,0 +1,19 @@
+@main def Test = {
+
+  println(
+    Tuple().flatMap[[t] =>> (t, t)]([t] => (x: t) => (x, x))
+  )
+
+  println(
+    (1, 2, "x", "d").flatMap[[t] =>> (t, t)]([t] => (x: t) => (x, x))
+  )
+
+  println(
+    (1, "x").flatMap[[t] =>> EmptyTuple]([t] => (x: t) => Tuple())
+  )
+
+  println(
+    (1, "x").flatMap[[t] =>> (t, String)]([t] => (x: t) => (x, x.toString + "!"))
+  )
+
+}