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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.collection
package generic
import mutable.Builder
import annotation.migration
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] <: GenTraversable[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.
* (or its `Iterable` superclass where class $Coll is not a `Seq`.)
*/
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]
private def sequential: TraversableOnce[A] = this.asInstanceOf[GenTraversableOnce[A]].seq
/** Converts this $coll of pairs into two collections of the first and second
* half 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 <- sequential) {
val (x, y) = asPair(xy)
b1 += x
b2 += y
}
(b1.result, b2.result)
}
/** Converts this $coll of triples into three collections of the first, second,
* and third element of each triple.
*
* @param A1 the type of the first member of the element triples
* @param A2 the type of the second member of the element triples
* @param A3 the type of the third member of the element triples
* @param asTriple an implicit conversion which asserts that the element type
* of this $coll is a triple.
* @return a triple ${coll}s, containing the first, second, respectively
* third member of each element triple of this $coll.
*/
def unzip3[A1, A2, A3](implicit asTriple: A => (A1, A2, A3)): (CC[A1], CC[A2], CC[A3]) = {
val b1 = genericBuilder[A1]
val b2 = genericBuilder[A2]
val b3 = genericBuilder[A3]
for (xyz <- sequential) {
val (x, y, z) = asTriple(xyz)
b1 += x
b2 += y
b3 += z
}
(b1.result, b2.result, b3.result)
}
/** Converts this $coll of traversable collections into
* a $coll formed by the elements of these traversable
* collections.
*
* The resulting collection's type will be guided by the
* static type of $coll. For example:
*
* {{{
* val xs = List(Set(1, 2, 3), Set(1, 2, 3))
* // xs == List(1, 2, 3, 1, 2, 3)
*
* val ys = Set(List(1, 2, 3), List(3, 2, 1))
* // ys == Set(1, 2, 3)
* }}}
*
* @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 => /*<:<!!!*/ TraversableOnce[B]): CC[B] = {
val b = genericBuilder[B]
for (xs <- sequential)
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.
* @throws `IllegalArgumentException` if all collections in this $coll
* are not of the same size.
*/
@migration("`transpose` throws an `IllegalArgumentException` if collections are not uniformly sized.", "2.9.0")
def transpose[B](implicit asTraversable: A => /*<:<!!!*/ GenTraversableOnce[B]): CC[CC[B] @uncheckedVariance] = {
if (isEmpty)
return genericBuilder[CC[B]].result
def fail = throw new IllegalArgumentException("transpose requires all collections have the same size")
val headSize = asTraversable(head).size
val bs: IndexedSeq[Builder[B, CC[B]]] = IndexedSeq.fill(headSize)(genericBuilder[B])
for (xs <- sequential) {
var i = 0
for (x <- asTraversable(xs)) {
if (i >= headSize) fail
bs(i) += x
i += 1
}
if (i != headSize)
fail
}
val bb = genericBuilder[CC[B]]
for (b <- bs) bb += b.result
bb.result
}
}
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