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package dotty.collections
package immutable
import annotation.unchecked.uncheckedVariance
trait Collection[+CC[X] <: Collection[CC, X], T] {
def companion: CollectionCompanion[CC]
}
trait Iterable[T] extends Collection[Iterable, T] {
def iterator: Iterator[T]
override def companion: IterableCompanion[Iterable] = Iterable
}
trait Seq[T] extends Iterable[T] with Collection[Seq, T] {
def apply(x: Int): T
override def companion: IterableCompanion[Seq] = Seq
}
abstract class CollectionCompanion[+CC[X] <: Collection[CC, X]]
trait IterableImpls[CC[X]] {
def fromIterator[T](it: Iterator[T]): CC[T]
def toIterator[T](xs: CC[T]): Iterator[T]
def map[T, U](xs: CC[T], f: T => U): CC[U] =
fromIterator(toIterator(xs).map(f))
def filter[T](xs: CC[T], p: T => Boolean): CC[T] =
fromIterator(toIterator(xs).filter(p))
def flatMap[T, U](xs: CC[T], f: T => TraversableOnce[U]): CC[U] =
fromIterator(toIterator(xs).flatMap(f))
}
abstract class IterableCompanion[+CC[X] <: Iterable[X] with Collection[CC, X]]
extends CollectionCompanion[CC] with IterableImpls[CC] @uncheckedVariance {
def toIterator[T](xs: CC[T] @uncheckedVariance) = xs.iterator
implicit def transformOps[T](xs: CC[T] @uncheckedVariance): TransformOps[CC, T] = new TransformOps[CC, T](xs)
}
class TransformOps[+CC[X] <: Iterable[X] with Collection[CC, X], T] (val xs: CC[T]) extends AnyVal {
def companion[T](xs: CC[T] @uncheckedVariance): IterableCompanion[CC] = xs.companion.asInstanceOf
def map[U](f: T => U): CC[U] = companion(xs).map(xs, f)
def filter(p: T => Boolean): CC[T] = companion(xs).filter(xs, p)
def flatMap[U](f: T => TraversableOnce[U]): CC[U] = companion(xs).flatMap(xs, f)
}
object Iterable extends IterableCompanion[Iterable] {
def fromIterator[T](it: Iterator[T]): Iterable[T] = ???
}
object Seq extends IterableCompanion[Seq] {
def fromIterator[T](it: Iterator[T]): Seq[T] = ???
}
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