scala.collection.generic.GenericCompanion.scala Maven / Gradle / Ivy
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala
package collection
package generic
import mutable.Builder
import scala.language.higherKinds
/** A template class for companion objects of "regular" collection classes
* represent an unconstrained higher-kinded type. Typically
* such classes inherit from trait `GenericTraversableTemplate`.
* @tparam CC The type constructor representing the collection class.
* @see [[scala.collection.generic.GenericTraversableTemplate]]
* @author Martin Odersky
* @since 2.8
* @define coll collection
* @define Coll `CC`
*/
abstract class GenericCompanion[+CC[X] <: GenTraversable[X]] {
/** The underlying collection type with unknown element type */
protected[this] type Coll = CC[_]
/** The default builder for `$Coll` objects.
* @tparam A the type of the ${coll}'s elements
*/
def newBuilder[A]: Builder[A, CC[A]]
/** An empty collection of type `$Coll[A]`
* @tparam A the type of the ${coll}'s elements
*/
def empty[A]: CC[A] = {
if ((this eq immutable.Seq) || (this eq collection.Seq)) Nil.asInstanceOf[CC[A]]
else newBuilder[A].result()
}
/** Creates a $coll with the specified elements.
* @tparam A the type of the ${coll}'s elements
* @param elems the elements of the created $coll
* @return a new $coll with elements `elems`
*/
def apply[A](elems: A*): CC[A] = {
if (elems.isEmpty) empty[A]
else {
val b = newBuilder[A]
b ++= elems
b.result()
}
}
}