From af2a0e66eb4b1204eac5dcb1d979486b92ef93d7 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sat, 9 Feb 2019 12:58:16 +0100
Subject: [PATCH] Add immutable array type

IArray[T] is an opaque alias for Array[T]
---
 library/src-bootstrapped/scala/IArray.scala | 60 +++++++++++++++++++++
 tests/run/iarrays.scala                     | 53 ++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 library/src-bootstrapped/scala/IArray.scala
 create mode 100644 tests/run/iarrays.scala

diff --git a/library/src-bootstrapped/scala/IArray.scala b/library/src-bootstrapped/scala/IArray.scala
new file mode 100644
index 000000000000..280c0557740d
--- /dev/null
+++ b/library/src-bootstrapped/scala/IArray.scala
@@ -0,0 +1,60 @@
+package scala
+import reflect.ClassTag
+
+/** It would be nice it IArray could be covariant, but unfortunately that's not
+ *  possible. The problem is the preculiar behavior of `Array[Any]`.
+ *  `Array[Any]` erases to `Object[]`. So, `IArray[Any]` also erases to `Object[]`.
+ *  Bit this means `IArray[Int]`, which erases to `Int[]`, cannot be a subtype of
+ *  `IArray[Any]`.
+ */
+opaque type IArray[T] = Array[T]
+
+object IArray {
+
+  implied arrayOps {
+    inline def (arr: IArray[T]) apply[T] (n: Int): T = (arr: Array[T]).apply(n)
+    inline def (arr: IArray[T]) length[T] : Int = (arr: Array[T]).length
+  }
+  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: _*)
+
+  def concat[T: ClassTag](xss: IArray[T]*): IArray[T] = Array.concat(xss: _*)
+
+  def fill[T: ClassTag](n: Int)(elem: => T): IArray[T] =
+    Array.fill(n)(elem)
+  def fill[T: ClassTag](n1: Int, n2: Int)(elem: => T): IArray[IArray[T]] =
+    Array.fill(n1, n2)(elem)
+  def fill[T: ClassTag](n1: Int, n2: Int, n3: Int)(elem: => T): IArray[IArray[IArray[T]]] =
+    Array.fill(n1, n2, n3)(elem)
+  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)
+  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)
+
+  def tabulate[T: ClassTag](n: Int)(f: Int => T): IArray[T] =
+    Array.tabulate(n)(f)
+  def tabulate[T: ClassTag](n1: Int, n2: Int)(f: (Int, Int) => T): IArray[IArray[T]] =
+    Array.tabulate(n1, n2)(f)
+  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)
+  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)
+  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)
+
+  def range(start: Int, end: Int): IArray[Int] = Array.range(start, end)
+  def range(start: Int, end: Int, step: Int): IArray[Int] = Array.range(start, end, step)
+
+  def iterate[T: ClassTag](start: T, len: Int)(f: T => T): IArray[T] = Array.iterate(start, len)(f)
+
+  def unapplySeq[T](x: IArray[T]): Option[IndexedSeq[T]] = Array.unapplySeq(x)
+}
\ No newline at end of file
diff --git a/tests/run/iarrays.scala b/tests/run/iarrays.scala
new file mode 100644
index 000000000000..a8d2b6dbfb9b
--- /dev/null
+++ b/tests/run/iarrays.scala
@@ -0,0 +1,53 @@
+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 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 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
+}
\ No newline at end of file