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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2010, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
// $Id$
package scala.collection
package generic
import mutable.Builder
import annotation.unchecked.uncheckedVariance
/** A template class for companion objects of ``regular'' collection classes
* that represent an unconstrained higher-kinded type.
* @tparam A The type of the collection elements.
* @tparam CC The type constructor representing the collection class.
* @author Martin Odersky
* @since 2.8
* @define coll collection
* @define Coll CC
*/
trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] {
/** Applies a function `f` to all elements of this $coll.
*
* @param f the function that is applied for its side-effect to every element.
* The result of function `f` is discarded.
*
* @tparam U the type parameter describing the result of function `f`.
* This result will always be ignored. Typically `U` is `Unit`,
* but this is not necessary.
*
* @usecase def foreach(f: A => Unit): Unit
*/
def foreach[U](f: A => U): Unit
/** Selects the first element of this $coll.
* @return the first element of this $coll.
* @throws `NoSuchElementException` if the $coll is empty.
*/
def head: A
/** Tests whether this $coll is empty.
*
* @return `true` if the $coll contain no elements, `false` otherwise.
*/
def isEmpty: Boolean
/** The factory companion object that builds instances of class $Coll.
*/
def companion: GenericCompanion[CC]
/** The builder that builds instances of type $Coll[A]
*/
protected[this] def newBuilder: Builder[A, CC[A]] = companion.newBuilder[A]
/** The generic builder that builds instances of $Coll
* at arbitrary element types.
*/
def genericBuilder[B]: Builder[B, CC[B]] = companion.newBuilder[B]
/** Converts this $coll of pairs into two collections of the first and second
* halfs of each pair.
* @param A1 the type of the first half of the element pairs
* @param A2 the type of the second half of the element pairs
* @param asPair an implicit conversion which asserts that the element type of this
* $coll is a pair.
* @return a pair ${coll}s, containing the first, respectively second half
* of each element pair of this $coll.
*/
def unzip[A1, A2](implicit asPair: A => /*<:<!!!*/ (A1, A2)): (CC[A1], CC[A2]) = {
val b1 = genericBuilder[A1]
val b2 = genericBuilder[A2]
for (xy <- this) {
val (x, y) = asPair(xy)
b1 += x
b2 += y
}
(b1.result, b2.result)
}
/** Converts this $coll of traversable collections into
* a $coll in which all element collections are concatenated.
* @tparam B the type of the elements of each traversable collection.
* @param asTraversable an implicit conversion which asserts that the element type of this
* $coll is a `Traversable`.
* @return a new $coll resulting from concatenating all element ${coll}s.
* @usecase def flatten[B]: $Coll[B]
*/
def flatten[B](implicit asTraversable: A => /*<:<!!!*/ Traversable[B]): CC[B] = {
val b = genericBuilder[B]
for (xs <- this)
b ++= asTraversable(xs)
b.result
}
/** Transposes this $coll of traversable collections into
* a $coll of ${coll}s.
* @tparam B the type of the elements of each traversable collection.
* @param asTraversable an implicit conversion which asserts that the element type of this
* $coll is a `Traversable`.
* @return a two-dimensional $coll of ${coll}s which has as ''n''th row
* the ''n''th column of this $coll.
*/
def transpose[B](implicit asTraversable: A => /*<:<!!!*/ Traversable[B]): CC[CC[B] @uncheckedVariance] = {
val bs: IndexedSeq[Builder[B, CC[B]]] = asTraversable(head).map(_ => genericBuilder[B]).toIndexedSeq
for (xs <- this) {
var i = 0
for (x <- asTraversable(xs)) {
bs(i) += x
i += 1
}
}
val bb = genericBuilder[CC[B]]
for (b <- bs) bb += b.result
bb.result
}
}
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