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Diffstat (limited to 'src')
-rw-r--r-- | src/dotty/collections/CollectionStrawMan1.scala | 330 |
1 files changed, 330 insertions, 0 deletions
diff --git a/src/dotty/collections/CollectionStrawMan1.scala b/src/dotty/collections/CollectionStrawMan1.scala new file mode 100644 index 000000000..211c8d7da --- /dev/null +++ b/src/dotty/collections/CollectionStrawMan1.scala @@ -0,0 +1,330 @@ +package strawman.collections + +import Predef.{augmentString => _, wrapString => _, _} +import scala.reflect.ClassTag +import collection.mutable.ListBuffer + +/** A strawman architecture for new collections. It contains some + * example collection classes and methods with the intent to expose + * some key issues. It would be good to compare this to other + * implementations of the same functionality, to get an idea of the + * strengths and weaknesses of different collection architectures. + * + * For a test file, see tests/run/CollectionTests.scala. + */ +object CollectionStrawMan1 { + + /* ------------ Base Traits -------------------------------- */ + + /** Replaces TraversableOnce */ + trait CanIterate[+A] { + def iterator: Iterator[A] + } + + /** Iterator guaranteed to be usable multiple times */ + trait HasIterator[+A] extends CanIterate[A] + + /** Base trait for instances that can construct a collection from an iterator */ + trait FromIterator[+C[X] <: Iterable[X]] { + def fromIterator[B](it: Iterator[B]): C[B] + } + + /** Base trait for companion objects of collections */ + trait IterableFactory[+C[X] <: Iterable[X]] extends FromIterator[C] { + def empty[X]: C[X] = fromIterator(Iterator.empty) + def apply[A](xs: A*): C[A] = fromIterator(Iterator(xs: _*)) + } + + /** Base trait for generic collections */ + trait Iterable[+IA] extends HasIterator[IA] with FromIterator[Iterable] { + def buildIterator: Iterator[IA] = iterator + } + + /** Base trait for sequence collections */ + trait Seq[+AA] extends Iterable[AA] with FromIterator[Seq] { + def apply(i: Int): AA + def length: Int + } + + /* ------------ Operations ----------------------------------- */ + + /** Operations returning types unrelated to current collection */ + trait Ops[A] extends Any { + def toIterator: Iterator[A] + def foreach(f: A => Unit): Unit = toIterator.foreach(f) + def foldLeft[B](z: B)(op: (B, A) => B): B = toIterator.foldLeft(z)(op) + def foldRight[B](z: B)(op: (A, B) => B): B = toIterator.foldRight(z)(op) + def indexWhere(p: A => Boolean): Int = toIterator.indexWhere(p) + def head: A = toIterator.next + def view: View[A] = new View(toIterator) + def collect[C[X] <: Iterable[X]](fi: FromIterator[C]): C[A] = fi.fromIterator(toIterator) + } + + /** Transforms returning same collection type */ + trait MonoTransforms[A, Repr] extends Any { + def toIterator: Iterator[A] + def fromIterator(it: => Iterator[A]): Repr + def partition(p: A => Boolean): (Repr, Repr) = { + val (xs, ys) = toIterator.partition(p) + (fromIterator(xs), fromIterator(ys)) + } + def drop(n: Int): Repr = fromIterator(toIterator.drop(n)) + } + + /** Transforms returning same collection type constructor */ + trait PolyTransforms[A, C[X]] extends Any { + def toIterator: Iterator[A] + def fromIterator[B](it: => Iterator[B]): C[B] + def map[B](f: A => B): C[B] = fromIterator(toIterator.map(f)) + def flatMap[B](f: A => CanIterate[B]): C[B] = fromIterator(toIterator.flatMap(f(_))) + def ++[B >: A](xs: CanIterate[B]): C[B] = fromIterator(toIterator ++ xs) + def zip[B](xs: CanIterate[B]): C[(A, B)] = fromIterator(toIterator.zip(xs.iterator)) + } + + /** Transforms that only apply to Seq */ + trait MonoTransformsOfSeqs[A, Repr] extends Any with MonoTransforms[A, Repr] { + def reverse: Repr = fromIterator(toIterator.reverse) + } + + /** Implementation of Ops for all generic collections */ + implicit class IterableOps[A](val c: Iterable[A]) + extends AnyVal with Ops[A] { + def toIterator = c.iterator + } + + /** Implementation of MonoTransforms for all generic collections */ + implicit class IterableMonoTransforms[A, C[X] <: Iterable[X]](val c: Iterable[A] with FromIterator[C]) + extends AnyVal with MonoTransforms[A, C[A]] { + def toIterator = c.buildIterator + def fromIterator(it: => Iterator[A]): C[A] = c.fromIterator(it) + } + + /** Implementation of PolyTransforms for all generic collections */ + implicit class IterablePolyTransforms[A, C[X] <: Iterable[X]](val c: Iterable[A] with FromIterator[C]) + extends AnyVal with PolyTransforms[A, C] { + def toIterator = c.buildIterator + def fromIterator[B](it: => Iterator[B]) = c.fromIterator(it) + } + + /** Implementation of MonoTransformsForSeqs for all generic collections */ + implicit class SeqMonoTransforms[A, C[X] <: Seq[X]](val c: Seq[A] with FromIterator[C]) + extends AnyVal with MonoTransformsOfSeqs[A, C[A]] { + def toIterator = c.buildIterator + def fromIterator(it: => Iterator[A]) = c.fromIterator(it) + } + + /* --------- Concrete collection types ------------------------------- */ + + /** Concrete collection type: List */ + sealed trait List[+A] extends Seq[A] with FromIterator[List] { + def isEmpty: Boolean + def head: A + def tail: List[A] + def iterator = new ListIterator[A](this) + def fromIterator[B](it: Iterator[B]): List[B] = List.fromIterator(it) + def apply(i: Int): A = { + require(!isEmpty) + if (i == 0) head else tail.apply(i - 1) + } + def length: Int = + if (isEmpty) 0 else 1 + tail.length + } + + case class Cons[+A](x: A, xs: List[A]) extends List[A] { + def isEmpty = false + def head = x + def tail = xs + } + + case object List extends IterableFactory[List] { + def fromIterator[B](it: Iterator[B]): List[B] = it match { + case it: ListIterator[B] => it.toList + case _ => if (it.hasNext) Cons(it.next, fromIterator(it)) else Nil + } + } + + class ListIterator[+A](xs: List[A]) extends Iterator[A] { + private[this] var current = xs + def hasNext = !current.isEmpty + def next = { val r = current.head; current = current.tail; r } + def toList = current + } + + case object Nil extends List[Nothing] { + def isEmpty = true + def head = ??? + def tail = ??? + } + + /** Concrete collection type: View */ + class View[+A](it: => Iterator[A]) extends HasIterator[A] { + def iterator = it + } + + implicit class ViewOps[A](val v: View[A]) extends AnyVal with Ops[A] { + def toIterator = v.iterator + def cache = collect(List).view + } + + implicit class ViewMonoTransforms[A](val v: View[A]) + extends AnyVal with MonoTransforms[A, View[A]] { + def toIterator = v.iterator + def fromIterator(it: => Iterator[A]): View[A] = new View(it) + } + + implicit class ViewPolyTransforms[A](val v: View[A]) + extends AnyVal with PolyTransforms[A, View] { + def toIterator = v.iterator + def fromIterator[B](it: => Iterator[B]) = new View(it) + } + + /** Concrete collection type: String */ + implicit class StringOps(val s: String) extends AnyVal with Ops[Char] { + def iterator: Iterator[Char] = new RandomAccessIterator[Char] { + def length = s.length + def apply(n: Int) = s.charAt(n) + } + def toIterator = iterator + } + + implicit class StringMonoTransforms(val s: String) + extends AnyVal with MonoTransformsOfSeqs[Char, String] { + def toIterator = s.iterator + def fromIterator(it: => Iterator[Char]) = { + val sb = new StringBuilder + for (ch <- it) sb.append(ch) + sb.toString + } + } + + implicit class StringPolyTransforms(val s: String) + extends AnyVal with PolyTransforms[Char, Seq] { + def toIterator = s.iterator + def fromIterator[B](it: => Iterator[B]) = List.fromIterator(it) + def map(f: Char => Char): String = { + val sb = new StringBuilder + for (ch <- s) sb.append(f(ch)) + sb.toString + } + def flatMap(f: Char => String) = { + val sb = new StringBuilder + for (ch <- s) sb.append(f(ch)) + sb.toString + } + def ++(xs: CanIterate[Char]): String = { + val sb = new StringBuilder(s) + for (ch <- xs.iterator) sb.append(ch) + sb.toString + } + def ++(xs: String): String = s + xs + } + +/* ---------- Iterators --------------------------------------------------- */ + + /** A core Iterator class */ + trait Iterator[+A] extends CanIterate[A] { self => + def hasNext: Boolean + def next: A + def iterator = this + def foldLeft[B](z: B)(op: (B, A) => B): B = + if (hasNext) foldLeft(op(z, next))(op) else z + def foldRight[B](z: B)(op: (A, B) => B): B = + if (hasNext) op(next, foldRight(z)(op)) else z + def foreach(f: A => Unit): Unit = + while (hasNext) f(next) + def indexWhere(p: A => Boolean): Int = { + var i = 0 + while (hasNext) { + if (p(next)) return i + i += 1 + } + -1 + } + def map[B](f: A => B): Iterator[B] = new Iterator[B] { + def hasNext = self.hasNext + def next = f(self.next) + } + def flatMap[B](f: A => CanIterate[B]): Iterator[B] = new Iterator[B] { + private var myCurrent: Iterator[B] = Iterator.empty + private def current = { + while (!myCurrent.hasNext && self.hasNext) myCurrent = f(self.next).iterator + myCurrent + } + def hasNext = current.hasNext + def next = current.next + } + def ++[B >: A](xs: CanIterate[B]): Iterator[B] = new Iterator[B] { + private var myCurrent: Iterator[B] = self + private def current = { + if (!myCurrent.hasNext && myCurrent.eq(self)) myCurrent = xs.iterator + myCurrent + } + def hasNext = current.hasNext + def next = current.next + } + def partition(p: A => Boolean): (Iterator[A], Iterator[A]) = { + val lookaheadTrue, lookaheadFalse = new ListBuffer[A] + class PartIterator[+A](buf: ListBuffer[A]) extends Iterator[A] { + final def hasNext: Boolean = + buf.nonEmpty || + self.hasNext && { + val elem = self.next + (if (p(elem)) lookaheadTrue else lookaheadFalse) += elem + hasNext + } + final def next = + if (hasNext) { + val r = buf.head + buf.trimStart(1) + r + } + else Iterator.nextOnEmpty + } + (new PartIterator(lookaheadTrue), new PartIterator(lookaheadFalse)) + } + def drop(n: Int): Iterator[A] = { + if (n <= 0) this + else { + next + drop(n - 1) + } + } + def zip[B](that: CanIterate[B]): Iterator[(A, B)] = new Iterator[(A, B)] { + val ti = that.iterator + def hasNext = self.hasNext && ti.hasNext + def next = (self.next, ti.next) + } + def reverse: Iterator[A] = { + var elems: List[A] = Nil + while (hasNext) elems = Cons(next, elems) + elems.iterator + } + } + + object Iterator { + val empty: Iterator[Nothing] = new Iterator[Nothing] { + def hasNext = false + def next = ??? + } + def apply[A](xs: A*): Iterator[A] = new RandomAccessIterator[A] { + def length = xs.length + def apply(n: Int) = xs(n) + } + def nextOnEmpty = throw new NoSuchElementException("next on empty iterator") + } + + trait RandomAccessIterator[+A] extends Iterator[A] { self => + def apply(n: Int): A + def length: Int + protected val len = length + private var cur = 0 + def hasNext = cur < len + def next: A = { val r = this(cur); cur += 1; r } + override def drop(n: Int): Iterator[A] = { cur += (n max 0); this } + override def reverse = new RandomAccessIterator[A] { + def length = self.length + def apply(n: Int) = apply(len - 1 - n) + } + } +} + |