Add an immutable array type

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1166,7 +1166,8 @@ object Types {
         else if (tp.symbol.isAliasType) tp.underlying.underlyingClassRef(refinementOK)
         else NoType
       case tp: AppliedType =>
-        tp.superType.underlyingClassRef(refinementOK)
+        if (tp.tycon.isLambdaSub) NoType
+        else tp.superType.underlyingClassRef(refinementOK)
       case tp: AnnotatedType =>
         tp.underlying.underlyingClassRef(refinementOK)
       case tp: RefinedType =>

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1737,7 +1737,12 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
     val app =
       typed(untpd.Apply(core, untpd.TypedSplice(receiver) :: Nil), pt1, ctx.typerState.ownedVars)(
         ctx.addMode(Mode.SynthesizeExtMethodReceiver))
-    if (!app.symbol.is(Extension))
+    val appSym =
+      app match {
+        case Inlined(call, _, _) => call.symbol
+        case _ => app.symbol
+      }
+    if (!appSym.is(Extension))
       ctx.error(em"not an extension method: $methodRef", receiver.sourcePos)
     app
   }

compiler/src/dotty/tools/dotc/typer/VarianceChecker.scala

@@ -48,6 +48,8 @@ object VarianceChecker {
             case tref: TypeParamRef if tref.binder `eq` tl =>
               val v = tl.typeParams(tref.paramNum).paramVariance
               varianceConforms(variance, v) || { error(tref); false }
+            case AnnotatedType(_, annot) if annot.symbol == defn.UncheckedVarianceAnnot =>
+              x
             case _ =>
               foldOver(x, t)
           }

library/src-bootstrapped/scala/IArray.scala

@@ -0,0 +1,196 @@
+package scala
+import reflect.ClassTag
+
+/** An immutable array. An `IArray[T]` has the same representation as an `Array[T]`,
+ *  but it cannot be updated. Unlike regular arrays, immutable arrays are covariant.
+ */
+opaque type IArray[+T] = Array[_ <: T]
+
+object IArray {
+
+  /** Defines extension methods for immutable arrays */
+  implied arrayOps {
+
+    /** The selection operation on an immutable array.
+     *
+     *  @param arr the immutable array
+     *  @param n   the index of the element to select
+     *  @return    the element of the array at the given index
+     */
+    inline def (arr: IArray[T]) apply[T] (n: Int): T = arr.asInstanceOf[Array[T]].apply(n)
+
+    /** The number of elements in an immutable array
+     *  @param arr  the immutable array
+     */
+    inline def (arr: IArray[T]) length[T] : Int = arr.asInstanceOf[Array[T]].length
+  }
+
+  /** An immutable array of length 0.
+   */
+  def empty[T: ClassTag]: IArray[T] = new Array[T](0)
+
+  /** An immutable array with given elements.
+   */
+  def apply[T: ClassTag](xs: T*): IArray[T] = Array(xs: _*)
+  def apply(x: Boolean, xs: Boolean*): IArray[Boolean] = Array(x, xs: _*)
+  def apply(x: Byte, xs: Byte*): IArray[Byte] = Array(x, xs: _*)
+  def apply(x: Short, xs: Short*): IArray[Short] = Array(x, xs: _*)
+  def apply(x: Char, xs: Char*): IArray[Char] = Array(x, xs: _*)
+  def apply(x: Int, xs: Int*): IArray[Int] = Array(x, xs: _*)
+  def apply(x: Long, xs: Long*): IArray[Long] = Array(x, xs: _*)
+  def apply(x: Float, xs: Float*): IArray[Float] = Array(x, xs: _*)
+  def apply(x: Double, xs: Double*): IArray[Double] = Array(x, xs: _*)
+  def apply(x: Unit, xs: Unit*): IArray[Unit] = Array(x, xs: _*)
+
+  /** Concatenates all arrays into a single immutable array.
+   *
+   *  @param xss the given immutable arrays
+   *  @return   the array created from concatenating `xss`
+   */
+  def concat[T: ClassTag](xss: IArray[T]*): IArray[T] = Array.concat[T](xss.asInstanceOf[Seq[Array[T]]]: _*)
+
+  /** Returns an immutable array that contains the results of some element computation a number
+   *  of times. Each element is determined by a separate computation.
+   *
+   *  @param   n  the number of elements in the array
+   *  @param   elem the element computation
+   */
+  def fill[T: ClassTag](n: Int)(elem: => T): IArray[T] =
+    Array.fill(n)(elem)
+
+  /** Returns a two-dimensional immutable array that contains the results of some element computation a number
+   *  of times. Each element is determined by a separate computation.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   elem the element computation
+   */
+  def fill[T: ClassTag](n1: Int, n2: Int)(elem: => T): IArray[IArray[T]] =
+    Array.fill(n1, n2)(elem)
+
+  /** Returns a three-dimensional immutable array that contains the results of some element computation a number
+   *  of times. Each element is determined by a separate computation.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   elem the element computation
+   */
+  def fill[T: ClassTag](n1: Int, n2: Int, n3: Int)(elem: => T): IArray[IArray[IArray[T]]] =
+    Array.fill(n1, n2, n3)(elem)
+
+  /** Returns a four-dimensional immutable array that contains the results of some element computation a number
+   *  of times. Each element is determined by a separate computation.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   elem the element computation
+   */
+  def fill[T: ClassTag](n1: Int, n2: Int, n3: Int, n4: Int)(elem: => T): IArray[IArray[IArray[IArray[T]]]] =
+    Array.fill(n1, n2, n3, n4)(elem)
+
+  /** Returns a five-dimensional immutable array that contains the results of some element computation a number
+   *  of times. Each element is determined by a separate computation.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   n5  the number of elements in the 5th dimension
+   *  @param   elem the element computation
+   */
+  def fill[T: ClassTag](n1: Int, n2: Int, n3: Int, n4: Int, n5: Int)(elem: => T): IArray[IArray[IArray[IArray[IArray[T]]]]] =
+    Array.fill(n1, n2, n3, n4, n5)(elem)
+
+  /** Returns an immutable array containing values of a given function over a range of integer
+   *  values starting from 0.
+   *
+   *  @param  n   The number of elements in the array
+   *  @param  f   The function computing element values
+   */
+  def tabulate[T: ClassTag](n: Int)(f: Int => T): IArray[T] =
+    Array.tabulate(n)(f)
+
+  /** Returns a two-dimensional immutable array containing values of a given function
+   *  over ranges of integer values starting from `0`.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   f   The function computing element values
+   */
+  def tabulate[T: ClassTag](n1: Int, n2: Int)(f: (Int, Int) => T): IArray[IArray[T]] =
+    Array.tabulate(n1, n2)(f)
+
+  /** Returns a three-dimensional immutable array containing values of a given function
+   *  over ranges of integer values starting from `0`.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3rd dimension
+   *  @param   f   The function computing element values
+   */
+  def tabulate[T: ClassTag](n1: Int, n2: Int, n3: Int)(f: (Int, Int, Int) => T): IArray[IArray[IArray[T]]] =
+    Array.tabulate(n1, n2, n3)(f)
+
+  /** Returns a four-dimensional immutable array containing values of a given function
+   *  over ranges of integer values starting from `0`.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3rd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   f   The function computing element values
+   */
+  def tabulate[T: ClassTag](n1: Int, n2: Int, n3: Int, n4: Int)(f: (Int, Int, Int, Int) => T): IArray[IArray[IArray[IArray[T]]]] =
+    Array.tabulate(n1, n2, n3, n4)(f)
+
+  /** Returns a five-dimensional immutable array containing values of a given function
+   *  over ranges of integer values starting from `0`.
+   *
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3rd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   n5  the number of elements in the 5th dimension
+   *  @param   f   The function computing element values
+   */
+  def tabulate[T: ClassTag](n1: Int, n2: Int, n3: Int, n4: Int, n5: Int)(f: (Int, Int, Int, Int, Int) => T): IArray[IArray[IArray[IArray[IArray[T]]]]] =
+    Array.tabulate(n1, n2, n3, n4, n5)(f)
+
+  /** Returns an immutable array containing a sequence of increasing integers in a range.
+   *
+   *  @param start  the start value of the array
+   *  @param end    the end value of the array, exclusive (in other words, this is the first value '''not''' returned)
+   *  @return  the immutable array with values in range `start, start + 1, ..., end - 1`
+   *  up to, but excluding, `end`.
+   */
+  def range(start: Int, end: Int): IArray[Int] = Array.range(start, end)
+
+  /** Returns an immutable array containing equally spaced values in some integer interval.
+   *
+   *  @param start the start value of the array
+   *  @param end   the end value of the array, exclusive (in other words, this is the first value '''not''' returned)
+   *  @param step  the increment value of the array (may not be zero)
+   *  @return      the immutable array with values in `start, start + step, ...` up to, but excluding `end`
+   */
+  def range(start: Int, end: Int, step: Int): IArray[Int] = Array.range(start, end, step)
+
+  /** Returns an immutable array containing repeated applications of a function to a start value.
+   *
+   *  @param start the start value of the array
+   *  @param len   the number of elements returned by the array
+   *  @param f     the function that is repeatedly applied
+   *  @return      the immutable array returning `len` values in the sequence `start, f(start), f(f(start)), ...`
+   */
+  def iterate[T: ClassTag](start: T, len: Int)(f: T => T): IArray[T] = Array.iterate(start, len)(f)
+
+  /** Returns a decomposition of the array into a sequence. This supports
+   *  a pattern match like `{ case IArray(x,y,z) => println('3 elements')}`.
+   *
+   *  @param x the selector value
+   *  @return  sequence wrapped in a [[scala.Some]], if `x` is a Seq, otherwise `None`
+   */
+   def unapplySeq[T](x: IArray[T]) = Array.unapplySeq[T](x.asInstanceOf[Array[T]])
+}

tests/neg/alloc-abstract.scala

@@ -0,0 +1,15 @@
+class Test[T] {
+  type U <: T
+
+  type Foo[T] = Array[T]
+
+  new T                   // error: not a class type
+  new T()                 // error: not a class type
+  new U                   // error: not a class type
+  new U()                 // error: not a class type
+  new IArray[String]      // error: not a class type
+  new IArray[String]()    // error: not a class type
+  new IArray[String](10)  // error: not a class type // error: too mamy arguments
+
+  new Foo[String](10)     // ok
+}

tests/neg/iarrays.scala

@@ -0,0 +1,15 @@
+object Test {
+
+  // Can't allocate an IArray
+  new IArray[String](10)  // error: not a class type // error: too many arguments
+
+  val xs = IArray(1, 2, 3)
+
+  // Can't have a wildcard IArray
+  val ys: IArray[_] = xs
+
+  // Can't update an IArray
+  xs(0) = 1    // error: value update is not a member
+  xs(1) += 1   // error: value += is not a member
+
+}

tests/neg/iarrays1.scala

@@ -0,0 +1,10 @@
+object Test {
+
+  // Can't allocate an IArray
+
+  val xs = IArray(1, 2, 3)
+
+  // Can't have a wildcard IArray
+  val ys: IArray[_] = xs   // error: unreducible application
+
+}

tests/neg/parser-stability-21.scala

@@ -1,3 +1,3 @@
 class x0[x1[]]    // error
-    extends x1[   // error
+    extends x1[
 // error

tests/pos/covariant-opaque.scala

@@ -0,0 +1,3 @@
+import annotation.unchecked.uncheckedVariance
+
+opaque type O[+T] = Array[T @uncheckedVariance]

tests/run/iarrays.scala

@@ -0,0 +1,73 @@
+import reflect.ClassTag
+object Test extends App {
+
+  val xs = IArray(1, 2, 3)
+
+  def f[T](ys: IArray[T]) = {
+    assert(ys.length == 3)
+    var sum = 0
+    for (i <- 0 until ys.length)
+      sum += xs(i)
+    assert(sum == 6)
+  }
+
+  f(xs)
+
+  var sum = 0
+  for (i <- 0 until xs.length)
+    sum += xs(i)
+  assert(sum == 6)
+
+  def reduce[T](xs: IArray[T], z: T, op: (T, T) => T) = {
+    var acc = z
+    for (i <- 0 until xs.length)
+      acc = op(acc, xs(i))
+    acc
+  }
+
+  def reduce2[T <: AnyRef](xs: IArray[T], z: T, op: (T, T) => T) = {
+    var acc = z
+    for (i <- 0 until xs.length)
+      acc = op(acc, xs(i))
+    acc
+  }
+
+  def flatten[T: ClassTag](ys: IArray[IArray[T]]) = {
+    var len = 0
+    for (i <- 0 until ys.length) len += ys(i).length
+    val flat = new Array[T](len)
+    var k = 0
+    for (i <- 0 until ys.length) {
+      for (j <- 0 until ys(i).length) {
+        flat(k) = ys(i)(j)
+        k += 1
+      }
+    }
+    IArray(flat: _*)
+  }
+
+  val ys = IArray.concat(xs, xs, xs)
+  assert(reduce(ys, 0, _ + _) == 18)
+
+  val ss = IArray("a", "b", "c")
+  assert(reduce2(ss, "", _ ++ _) == "abc")
+
+  val zss = IArray.fill(2, 3)(1)
+  val zs = flatten(zss)
+  assert(reduce(zs, 0, _ + _) == 6)
+
+  val is = IArray.iterate(0, 4)(_ + 1)
+  assert(reduce(is, 0, _ + _) == 6)
+
+  val IArray(1, 2, 3) = xs
+
+  val as: IArray[Any] = IArray(1, "hello")
+  assert(as(as.length - 1) == "hello")
+  assert(reduce(as, 0, (x, y) => x.toString ++ y.toString) == "01hello")
+
+  // Check that representation of IArray and Array is the same
+  val bs: IArray[Double] = IArray(1.0, 2.0)
+  val cs: Array[Double] = bs.asInstanceOf[Array[Double]]
+  cs(1) = 3.0
+  assert(bs(1) == 3.0)
+}