Add NamedTuple object to library

Author: odersky

library/src/scala/NamedTuple.scala

@@ -0,0 +1,112 @@
+package scala
+import annotation.experimental
+import compiletime.ops.boolean.*
+
+@experimental
+object NamedTuple:
+
+  opaque type AnyNamedTuple = Any
+  opaque type NamedTuple[N <: Tuple, V <: Tuple] >: V <: AnyNamedTuple = V
+
+  def apply[N <: Tuple, V <: Tuple](x: V) = x
+
+  def unapply[N <: Tuple, V <: Tuple](x: NamedTuple[N, V]): Some[V] = Some(x)
+
+  extension [V <: Tuple](x: V)
+    inline def withNames[N <: Tuple]: NamedTuple[N, V] = x
+
+  extension [N <: Tuple, V <: Tuple](x: NamedTuple[N, V])
+
+    inline def values: V = x
+
+    inline def size: Tuple.Size[V] = values.size
+
+    // This intentionally works for empty named tuples as well. I think NnEmptyTuple is a dead end
+    // and should be reverted, justy like NonEmptyList is also appealing at first, but a bad idea
+    // in the end.
+    inline def apply(n: Int): Tuple.Elem[V, n.type] =
+      inline values match
+        case tup: NonEmptyTuple => tup(n).asInstanceOf[Tuple.Elem[V, n.type]]
+        case tup => tup.productElement(n).asInstanceOf[Tuple.Elem[V, n.type]]
+
+    inline def head: Tuple.Elem[V, 0] = apply(0)
+    inline def tail: Tuple.Drop[V, 1] = values.drop(1)
+
+    inline def last: Tuple.Last[V] = apply(size - 1).asInstanceOf[Tuple.Last[V]]
+    inline def init: Tuple.Init[V] = values.take(size - 1).asInstanceOf[Tuple.Init[V]]
+
+    inline def take(n: Int): NamedTuple[Tuple.Take[N, n.type], Tuple.Take[V, n.type]] =
+      values.take(n)
+
+    inline def drop(n: Int): NamedTuple[Tuple.Drop[N, n.type], Tuple.Drop[V, n.type]] =
+      values.drop(n)
+
+    inline def splitAt(n: Int): NamedTuple[Tuple.Split[N, n.type], Tuple.Split[V, n.type]] =
+      values.splitAt(n)
+
+    inline def ++ [N2 <: Tuple, V2 <: Tuple](that: NamedTuple[N2, V2])(using Tuple.Disjoint[N, N2] =:= true)
+      : NamedTuple[Tuple.Concat[N, N2], Tuple.Concat[V, V2]]
+      = values ++ that.values
+
+    // inline def :* [L] (x: L): NamedTuple[Append[N, ???], Append[V, L] = ???
+    // inline def *: [H] (x: H): NamedTuple[??? *: N], H *: V] = ???
+
+    inline def map[F[_]](f: [t] => t => F[t]): NamedTuple[N, Tuple.Map[V, F]] =
+      values.map(f).asInstanceOf[NamedTuple[N, Tuple.Map[V, F]]]
+
+    inline def reverse: NamedTuple[Tuple.Reverse[N], Tuple.Reverse[V]] =
+      values.reverse
+
+    inline def zip[V2 <: Tuple](that: NamedTuple[N, V2]): NamedTuple[N, Tuple.Zip[V, V2]] =
+      values.zip(that.values)
+
+    inline def toList: List[Tuple.Union[V]] = values.toList.asInstanceOf[List[Tuple.Union[V]]]
+    inline def toArray: Array[Object] = values.toArray
+    inline def toIArray: IArray[Object] = values.toIArray
+
+  end extension
+
+  /** The names of the named tuple type `NT` */
+  type Names[NT <: AnyNamedTuple] <: Tuple = NT match
+    case NamedTuple[n, _] => n
+
+  /** The value types of the named tuple type `NT` */
+  type DropNames[NT <: AnyNamedTuple] <: Tuple = NT match
+    case NamedTuple[_, x] => x
+
+  type Size[X <: AnyNamedTuple] = Tuple.Size[DropNames[X]]
+
+  type Elem[X <: AnyNamedTuple, N <: Int] = Tuple.Elem[DropNames[X], N]
+
+  type Head[X <: AnyNamedTuple] = Elem[X, 0]
+
+  type Last[X <: AnyNamedTuple] = Tuple.Last[DropNames[X]]
+
+  type Init[X <: AnyNamedTuple] =
+    NamedTuple[Tuple.Init[Names[X]], Tuple.Init[DropNames[X]]]
+
+  type Tail[X <: AnyNamedTuple] = Drop[X, 1]
+
+  type Take[X <: AnyNamedTuple, N <: Int] =
+    NamedTuple[Tuple.Take[Names[X], N], Tuple.Take[DropNames[X], N]]
+
+  type Drop[X <: AnyNamedTuple, N <: Int] =
+    NamedTuple[Tuple.Drop[Names[X], N], Tuple.Drop[DropNames[X], N]]
+
+  type Split[X <: AnyNamedTuple, N <: Int] = (Take[X, N], Drop[X, N])
+
+  type Concat[X <: AnyNamedTuple, Y <: AnyNamedTuple] =
+    NamedTuple[Tuple.Concat[Names[X], Names[Y]], Tuple.Concat[DropNames[X], DropNames[Y]]]
+
+  type Map[X <: AnyNamedTuple, F[_ <: Tuple.Union[DropNames[X]]]] =
+    NamedTuple[Names[X], Tuple.Map[DropNames[X], F]]
+
+  type Reverse[X <: AnyNamedTuple] =
+    NamedTuple[Tuple.Reverse[Names[X]], Tuple.Reverse[DropNames[X]]]
+
+  type Zip[X <: AnyNamedTuple, Y <: AnyNamedTuple] =
+    Tuple.Conforms[Names[X], Names[Y]] match
+      case true =>
+        NamedTuple[Names[X], Tuple.Zip[DropNames[X], DropNames[Y]]]
+
+end NamedTuple