Specialized traits design draft

Author: odersky

tests/pos/specialized-traits-strawman.scala

@@ -0,0 +1,142 @@
+import language.experimental.erasedDefinitions
+
+// Source code
+
+/*inline*/ trait Iterator[T/*: Specialized*/]:
+  def hasNext: Boolean
+  def next(): T
+
+/*inline*/ trait ArrayIterator[T/*: Specialized*/](elems: Array[T]) extends Iterator[T]:
+  private var current = 0
+  def hasNext: Boolean = current < elems.length
+  def next(): T = try elems(current) finally current += 1
+
+/*inline*/ trait Iterable[T/*: Specialized*/]:
+  def iterator: Iterator[T]
+  def forall(f: T => Unit): Unit =
+    val it = iterator
+    while it.hasNext do f(it.next())
+
+/*inline*/ trait Vec[T/*: Specialized*/](elems: Array[T])
+extends Iterable[T]:
+  def length: Int           = elems.length
+  def apply(i: Int): T      = elems(i)
+  def iterator: Iterator[T] = new ArrayIterator[T](elems) {}
+
+// Specialized trait APIs generated from specialization:
+
+trait Iterator_Int extends Iterator[Int]:
+  def hasNext: Boolean
+  def next(): Int
+
+trait ArrayIterator_Int extends ArrayIterator[Int], Iterator[Int]
+
+trait Iterable_Int extends Iterable[Int]:
+  def iterator: Iterator_Int
+  def forall(f: Int => Unit): Unit
+
+trait Vec_Int extends Vec[Int], Iterable[Int]:
+  def length: Int
+  def apply(i: Int): Int
+
+class ArrayIterator_Int$impl(elems: Array[Int]) extends ArrayIterator_Int
+    , ArrayIterator[Int](elems): // snd parent not needed in actual translation
+  private var current = 0
+  override def hasNext: Boolean =
+    current < elems.length
+  override def next(): Int =
+    try elems(current) finally current += 1
+
+class Vec_Int$impl(elems: Array[Int]) extends Vec_Int
+    , Vec[Int](elems):        // snd parent not needed in actual translation
+  override def iterator: Iterator_Int =
+    new ArrayIterator_Int$impl(elems).asInstanceOf
+      // cast needed since the compiler does not not know that Iterable[Int] = Iterable_Int
+      // after erasure. No cast would be needed in the actual translation.
+
+  override def forall(f: Int => Unit): Unit =
+    val it = iterator
+    while it.hasNext do f(it.next())
+  override def length: Int = elems.length
+  override def apply(i: Int): Int = elems(i)
+
+// Inline trait APIs generated from inline traits transform:
+object InlineTraitAPIs:
+
+  trait Iterator[T]:
+    def hasNext: Boolean
+    def next(): T
+
+  trait ArrayIterator[T] extends Iterator[T]
+
+  trait Iterable[T]:
+    def iterator: Iterator[T]
+    def forall(f: T => Unit): Unit
+
+  trait Vec[T] extends Iterable[T]:
+    def length: Int
+    def apply(i: Int): T
+end InlineTraitAPIs
+
+/* Code after erasure: */
+object AfterErasure:
+
+  trait Function1:
+    def apply(x: Any): Any
+    def apply_Int_Unit(x: Int): Unit
+
+  trait Iterator:
+    def hasNext: Boolean
+    def next(): Any
+
+  trait ArrayIterator extends Iterator
+
+  trait Iterable:
+    def iterator: Iterator
+    def forall(f: Function1): Unit
+
+  trait Vec:
+    def length: Int
+    def apply(i: Int): Any
+
+  trait Iterator_Int extends Iterator:
+    def hasNext: Boolean
+    def next(): Int
+
+  trait ArrayIterator_Int extends ArrayIterator, Iterator_Int
+
+  trait Iterable_Int extends Iterable:
+    def iterator: Iterator_Int
+    def forall(f: Function1): Unit
+
+  trait Vec_Int extends Vec, Iterable_Int:
+    def length: Int
+    def apply(i: Int): Int
+
+  class ArrayIterator_Int$impl(elems: Array[Int]) extends ArrayIterator_Int:
+    private var current = 0
+    override def hasNext: Boolean =
+      current < elems.length
+    override def next(): Int =
+      try elems(current) finally current += 1
+
+    /* Bridges:
+    override def next(): Any = Int.box(next())
+    */
+  end ArrayIterator_Int$impl
+
+  class Vec_Int$impl(elems: Array[Int]) extends Vec_Int:
+    override def iterator: Iterator_Int =
+      new ArrayIterator_Int$impl(elems)
+    override def forall(f: Function1): Unit =
+      val it = iterator
+      while it.hasNext do f.apply_Int_Unit(it.next())
+    override def length: Int = elems.length
+    override def apply(i: Int): Int = elems(i)
+
+    /* Bridges:
+    override def iterator: Iterator = iterator
+    override def apply(i: Int): Any = Int.box(apply(i))
+    */
+  end Vec_Int$impl
+