From b8472d8c6e6c9a267088817eb8e05577e5eda60b Mon Sep 17 00:00:00 2001 From: Martin Odersky Date: Sun, 17 Apr 2016 16:42:40 +0200 Subject: Updates of strawman Bring strawman-4 and strawman-5 to feature-parity. Test also strawman-4. --- src/strawman/collections/CollectionStrawMan4.scala | 109 +++++++++++++++------ src/strawman/collections/CollectionStrawMan5.scala | 88 +++++++++-------- 2 files changed, 130 insertions(+), 67 deletions(-) (limited to 'src/strawman') diff --git a/src/strawman/collections/CollectionStrawMan4.scala b/src/strawman/collections/CollectionStrawMan4.scala index 8ec77e19b..874f67a2d 100644 --- a/src/strawman/collections/CollectionStrawMan4.scala +++ b/src/strawman/collections/CollectionStrawMan4.scala @@ -2,6 +2,8 @@ package strawman.collections import Predef.{augmentString => _, wrapString => _, _} import scala.reflect.ClassTag +import annotation.unchecked.uncheckedVariance +import annotation.tailrec /** A strawman architecture for new collections. It contains some * example collection classes and methods with the intent to expose @@ -20,13 +22,6 @@ object CollectionStrawMan4 { def iterator: Iterator[A] } - /** Base trait for generic collections */ - trait Iterable[+A] extends IterableOnce[A] with FromIterable[Iterable] { - def iterator: Iterator[A] - def view: View[A] = View.fromIterator(iterator) - def knownLength: Int = -1 - } - /** Base trait for instances that can construct a collection from an iterable */ trait FromIterable[+C[X] <: Iterable[X]] { def fromIterable[B](v: Iterable[B]): C[B] @@ -38,16 +33,27 @@ object CollectionStrawMan4 { def apply[A](xs: A*): C[A] = fromIterable(View.Elems(xs: _*)) } + /** Base trait for generic collections */ + trait Iterable[+A] extends IterableOnce[A] with FromIterable[Iterable] { + def view: View[A] = View.fromIterator(iterator) // view is overridden, cannot be defined in ops + def knownLength: Int = -1 + } + /** Base trait for sequence collections */ trait Seq[+A] extends Iterable[A] with FromIterable[Seq] { def apply(i: Int): A def length: Int } + /** Base trait for collection builders */ trait Builder[-A, +To] { def +=(x: A): this.type - def ++=(xs: IterableOnce[A]): Unit = xs.iterator.foreach(+=) def result: To + + def ++=(xs: IterableOnce[A]): this.type = { + xs.iterator.foreach(+=) + this + } } /* ------------ Operations ----------------------------------- */ @@ -134,17 +140,18 @@ object CollectionStrawMan4 { require(!isEmpty) if (i == 0) head else tail.apply(i - 1) } - def :::[B >: A](prefix: List[B]): List[B] = - if (prefix.isEmpty) this - else Cons(prefix.head, prefix.tail ::: this) def length: Int = if (isEmpty) 0 else 1 + tail.length + def ++:[B >: A](prefix: List[B]): List[B] = + if (prefix.isEmpty) this + else Cons(prefix.head, prefix.tail ++: this) } - case class Cons[+A](x: A, xs: List[A]) extends List[A] { + case class Cons[+A](x: A, private[collections] var next: List[A @uncheckedVariance]) // sound because `next` is used only locally + extends List[A] { def isEmpty = false def head = x - def tail = xs + def tail = next } case object Nil extends List[Nothing] { @@ -157,20 +164,64 @@ object CollectionStrawMan4 { def fromIterator[B](it: Iterator[B]): List[B] = if (it.hasNext) Cons(it.next, fromIterator(it)) else Nil def fromIterable[B](c: Iterable[B]): List[B] = c match { - case View.Concat(xs, ys: Iterable[B]) => - fromIterable(xs) ::: fromIterable(ys) + case View.Concat(xs, ys: List[B]) => + fromIterable(xs) ++: ys case View.Drop(xs: List[B], n) => - var i = 0 - var ys = xs - while (i < n && !xs.isEmpty) { - ys = ys.tail - i += 1 - } - ys + @tailrec def loop(xs: List[B], n: Int): List[B] = + if (n > 0) loop(xs.tail, n - 1) else xs + loop(xs, n) + case c: List[B] => c case _ => fromIterator(c.iterator) } } + /** Concrete collection type: ListBuffer */ + class ListBuffer[A] extends Seq[A] with FromIterable[ListBuffer] with Builder[A, List[A]] { + private var first, last: List[A] = Nil + private var aliased = false + def iterator = first.iterator + def fromIterable[B](coll: Iterable[B]) = ListBuffer.fromIterable(coll) + def apply(i: Int) = first.apply(i) + def length = first.length + + private def copyElems(): Unit = { + val buf = ListBuffer.fromIterable(result) + first = buf.first + last = buf.last + aliased = false + } + def result = { + aliased = true + first + } + def +=(elem: A) = { + if (aliased) copyElems() + val last1 = Cons(elem, Nil) + last match { + case last: Cons[A] => last.next = last1 + case _ => first = last1 + } + last = last1 + this + } + override def toString: String = + if (first.isEmpty) "ListBuffer()" + else { + val b = new StringBuilder("ListBuffer(").append(first.head) + first.tail.foldLeft(b)(_.append(", ").append(_)).append(")").toString + } + } + + object ListBuffer extends IterableFactory[ListBuffer] { + def fromIterable[B](coll: Iterable[B]): ListBuffer[B] = coll match { + case pd @ View.Partitioned(partition: View.Partition[B]) => + partition.distribute(new ListBuffer[B]()) + pd.forced.get.asInstanceOf[ListBuffer[B]] + case _ => + new ListBuffer[B] ++= coll + } + } + /** Concrete collection type: ArrayBuffer */ class ArrayBuffer[A] private (initElems: Array[AnyRef], initLength: Int) extends Seq[A] with FromIterable[ArrayBuffer] with Builder[A, ArrayBuffer[A]] { @@ -234,12 +285,6 @@ object CollectionStrawMan4 { def apply(n: Int) = elems(start + n).asInstanceOf[A] } - case class StringView(s: String) extends RandomAccessView[Char] { - val start = 0 - val end = s.length - def apply(n: Int) = s.charAt(n) - } - /** Concrete collection type: String */ implicit class StringOps(val s: String) extends AnyVal with Ops[Char] { def iterator: Iterator[Char] = new StringView(s).iterator @@ -277,6 +322,12 @@ object CollectionStrawMan4 { def ++(xs: String): String = s + xs } + case class StringView(s: String) extends RandomAccessView[Char] { + val start = 0 + val end = s.length + def apply(n: Int) = s.charAt(n) + } + /* ------------ Views --------------------------------------- */ /** A lazy iterable */ @@ -322,6 +373,8 @@ object CollectionStrawMan4 { } case class Partition[A](val underlying: Iterable[A], p: A => Boolean) { val left, right = Partitioned(this) + // `distribute` makes up for the lack of generic push-based functionality. + // It forces both halves of the partition with a given builder. def distribute(bf: => Builder[A, Iterable[A]]) = { val lb, rb = bf val it = underlying.iterator diff --git a/src/strawman/collections/CollectionStrawMan5.scala b/src/strawman/collections/CollectionStrawMan5.scala index cfca6cd31..1a89d9659 100644 --- a/src/strawman/collections/CollectionStrawMan5.scala +++ b/src/strawman/collections/CollectionStrawMan5.scala @@ -3,6 +3,7 @@ package strawman.collections import Predef.{augmentString => _, wrapString => _, _} import scala.reflect.ClassTag import annotation.unchecked.uncheckedVariance +import annotation.tailrec /** A strawman architecture for new collections. It contains some * example collection classes and methods with the intent to expose @@ -32,24 +33,8 @@ object CollectionStrawMan5 { def apply[A](xs: A*): C[A] = fromIterable(View.Elems(xs: _*)) } - /** Base trait for Iterable operations */ - trait IterableLike[+A, +C[X] <: Iterable[X]] - extends FromIterable[C] - with IterableOps[A] - with IterableMonoTransforms[A @uncheckedVariance, C[A @uncheckedVariance]] - with IterablePolyTransforms[A @uncheckedVariance, C] { - protected[this] def fromLikeIterable(coll: Iterable[A]): C[A] = fromIterable(coll) - } - - /** Base trait for Seq operations */ - trait SeqLike[+A, +C[X] <: Seq[X]] - extends IterableLike[A, C] with SeqMonoTransforms[A @uncheckedVariance, C[A @uncheckedVariance]] - /** Base trait for generic collections */ trait Iterable[+A] extends IterableOnce[A] with IterableLike[A, Iterable] { - override def iterator: Iterator[A] - override def fromIterable[B](it: Iterable[B]): Iterable[B] - protected def coll: Iterable[A] = this def knownLength: Int = -1 } @@ -58,9 +43,9 @@ object CollectionStrawMan5 { trait Seq[+A] extends Iterable[A] with SeqLike[A, Seq] { def apply(i: Int): A def length: Int - override def iterator: Iterator[A] } + /** Base trait for strict collections */ trait Buildable[+A, +To <: Iterable[A]] extends Iterable[A] { protected[this] def newBuilder: Builder[A, To] override def partition(p: A => Boolean): (To, To) = { @@ -68,8 +53,11 @@ object CollectionStrawMan5 { iterator.foreach(x => (if (p(x)) l else r) += x) (l.result, r.result) } + // one might also override other transforms here to avoid generating + // iterators if it helps efficiency. } + /** Base trait for collection builders */ trait Builder[-A, +To] { def +=(x: A): this.type def result: To @@ -82,6 +70,29 @@ object CollectionStrawMan5 { /* ------------ Operations ----------------------------------- */ + /** Base trait for Iterable operations + * + * VarianceNote + * ============ + * + * We require that for all child classes of Iterable the variance of + * the child class and the variance of the `C` parameter passed to `IterableLike` + * are the same. We cannot express this since we lack variance polymorphism. That's + * why we have to resort at some places to write `C[A @uncheckedVariance]`. + * + */ + trait IterableLike[+A, +C[X] <: Iterable[X]] + extends FromIterable[C] + with IterableOps[A] + with IterableMonoTransforms[A, C[A @uncheckedVariance]] // sound bcs of VarianceNote + with IterablePolyTransforms[A, C] { + protected[this] def fromLikeIterable(coll: Iterable[A]): C[A] = fromIterable(coll) + } + + /** Base trait for Seq operations */ + trait SeqLike[+A, +C[X] <: Seq[X]] + extends IterableLike[A, C] with SeqMonoTransforms[A, C[A @uncheckedVariance]] // sound bcs of VarianceNote + trait IterableOps[+A] extends Any { def iterator: Iterator[A] def foreach(f: A => Unit): Unit = iterator.foreach(f) @@ -93,16 +104,19 @@ object CollectionStrawMan5 { def view: View[A] = View.fromIterator(iterator) } - trait IterableMonoTransforms[A, +Repr] extends Any { + trait IterableMonoTransforms[+A, +Repr] extends Any { protected def coll: Iterable[A] - protected def fromLikeIterable(coll: Iterable[A]): Repr + protected[this] def fromLikeIterable(coll: Iterable[A]): Repr def filter(p: A => Boolean): Repr = fromLikeIterable(View.Filter(coll, p)) def partition(p: A => Boolean): (Repr, Repr) = { val pn = View.Partition(coll, p) (fromLikeIterable(pn.left), fromLikeIterable(pn.right)) } def drop(n: Int): Repr = fromLikeIterable(View.Drop(coll, n)) - def to[C[X] <: Iterable[X]](fi: FromIterable[C]): C[A] = fi.fromIterable(coll) + def to[C[X] <: Iterable[X]](fi: FromIterable[C]): C[A @uncheckedVariance] = + // variance seems sound because `to` could just as well have been added + // as a decorator. We should investigate this further to be sure. + fi.fromIterable(coll) } trait IterablePolyTransforms[+A, +C[A]] extends Any { @@ -112,9 +126,10 @@ object CollectionStrawMan5 { def flatMap[B](f: A => IterableOnce[B]): C[B] = fromIterable(View.FlatMap(coll, f)) def ++[B >: A](xs: IterableOnce[B]): C[B] = fromIterable(View.Concat(coll, xs)) def zip[B](xs: IterableOnce[B]): C[(A @uncheckedVariance, B)] = fromIterable(View.Zip(coll, xs)) + // sound bcs of VarianceNote } - trait SeqMonoTransforms[A, +Repr] extends Any with IterableMonoTransforms[A, Repr] { + trait SeqMonoTransforms[+A, +Repr] extends Any with IterableMonoTransforms[A, Repr] { def reverse: Repr = { var xs: List[A] = Nil var it = coll.iterator @@ -150,10 +165,12 @@ object CollectionStrawMan5 { case xs: List[B] => this ++: xs case _ => super.++(xs) } - override def reverse = super.reverse + @tailrec final override def drop(n: Int) = + if (n > 0) tail.drop(n - 1) else this } - case class Cons[+A](x: A, private[collections] var next: List[A @uncheckedVariance]) extends List[A] { + case class Cons[+A](x: A, private[collections] var next: List[A @uncheckedVariance]) // sound because `next` is used only locally + extends List[A] { override def isEmpty = false override def head = x def tail = next @@ -176,11 +193,7 @@ object CollectionStrawMan5 { class ListBuffer[A] extends Seq[A] with SeqLike[A, ListBuffer] with Builder[A, List[A]] { private var first, last: List[A] = Nil private var aliased = false - def iterator = new Iterator[A] { - var current: List[A] = first - def hasNext = ??? - def next = ??? - } + def iterator = first.iterator def fromIterable[B](coll: Iterable[B]) = ListBuffer.fromIterable(coll) def apply(i: Int) = first.apply(i) def length = first.length @@ -205,6 +218,12 @@ object CollectionStrawMan5 { last = last1 this } + override def toString: String = + if (first.isEmpty) "ListBuffer()" + else { + val b = new StringBuilder("ListBuffer(").append(first.head) + first.tail.foldLeft(b)(_.append(", ").append(_)).append(")").toString + } } object ListBuffer extends IterableFactory[ListBuffer] { @@ -291,12 +310,12 @@ object CollectionStrawMan5 { def fromIterable[B](coll: Iterable[B]): List[B] = List.fromIterable(coll) def map(f: Char => Char): String = { val sb = new StringBuilder - for (ch <- StringOps(s)) sb.append(f(ch)) + for (ch <- s) sb.append(f(ch)) sb.toString } def flatMap(f: Char => String): String = { val sb = new StringBuilder - for (ch <- StringOps(s)) sb.append(f(ch)) + for (ch <- s) sb.append(f(ch)) sb.toString } def ++(xs: IterableOnce[Char]): String = { @@ -393,15 +412,6 @@ object CollectionStrawMan5 { -1 } } - case class Reverse[A](underlying: Iterable[A]) extends View[A] { - def iterator = { - var xs: List[A] = Nil - val it = underlying.iterator - while (it.hasNext) xs = Cons(it.next(), xs) - xs.iterator - } - override def knownLength = underlying.knownLength - } } /* ---------- Iterators ---------------------------------------------------*/ -- cgit v1.2.3