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    30 
    31   /*                     __                                               *\
    32   **     ________ ___   / /  ___     Scala API                            **
    33   **    / __/ __// _ | / /  / _ |    (c) 2003-2011, LAMP/EPFL             **
    34   **  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
    35   ** /____/\___/_/ |_/____/_/ | |                                         **
    36   **                          |/                                          **
    37   \*                                                                      */
    38 
    39   package scala.collection
    40 
    41   import generic._
    42   import mutable.{ Builder, ListBuffer }
    43   import annotation.{tailrec, migration, bridge}
    44   import annotation.unchecked.{ uncheckedVariance => uV }
    45   import parallel.ParIterable
    46 
    47   /** A template trait for traversable collections of type `Traversable[A]`.
    48    *  
    49    *  $traversableInfo
    50    *  @define mutability
    51    *  @define traversableInfo
    52    *  This is a base trait of all kinds of $mutability Scala collections. It
    53    *  implements the behavior common to all collections, in terms of a method
    54    *  `foreach` with signature:
    55    * {{{
    56    *     def foreach[U](f: Elem => U): Unit
    57    * }}}
    58    *  Collection classes mixing in this trait provide a concrete 
    59    *  `foreach` method which traverses all the
    60    *  elements contained in the collection, applying a given function to each.
    61    *  They also need to provide a method `newBuilder`
    62    *  which creates a builder for collections of the same kind.
    63    *  
    64    *  A traversable class might or might not have two properties: strictness
    65    *  and orderedness. Neither is represented as a type.
    66    *  
    67    *  The instances of a strict collection class have all their elements
    68    *  computed before they can be used as values. By contrast, instances of
    69    *  a non-strict collection class may defer computation of some of their
    70    *  elements until after the instance is available as a value.
    71    *  A typical example of a non-strict collection class is a
    72    *  <a href="../immutable/Stream.html" target="ContentFrame">
    73    *  `scala.collection.immutable.Stream`</a>.
    74    *  A more general class of examples are `TraversableViews`.
    75    *  
    76    *  If a collection is an instance of an ordered collection class, traversing
    77    *  its elements with `foreach` will always visit elements in the
    78    *  same order, even for different runs of the program. If the class is not
    79    *  ordered, `foreach` can visit elements in different orders for
    80    *  different runs (but it will keep the same order in the same run).'
    81    * 
    82    *  A typical example of a collection class which is not ordered is a
    83    *  `HashMap` of objects. The traversal order for hash maps will
    84    *  depend on the hash codes of its elements, and these hash codes might
    85    *  differ from one run to the next. By contrast, a `LinkedHashMap`
    86    *  is ordered because it's `foreach` method visits elements in the
    87    *  order they were inserted into the `HashMap`.
    88    *
    89    *  @author Martin Odersky
    90    *  @version 2.8
    91    *  @since   2.8
    92    *  @tparam A    the element type of the collection
    93    *  @tparam Repr the type of the actual collection containing the elements.
    94    *
    95    *  @define Coll Traversable
    96    *  @define coll traversable collection
    97    */
    98   trait TraversableLike[+A, +Repr] extends HasNewBuilder[A, Repr] 
    99                                       with FilterMonadic[A, Repr]
   100                                       with TraversableOnce[A]
   101                                       with GenTraversableLike[A, Repr]
   102                                       with Parallelizable[A, ParIterable[A]]
   103   {
   104     self =>
   105 
   106     import Traversable.breaks._
   107 
   108     /** The type implementing this traversable */
   109     protected type Self = Repr
   110 
   111     /** The collection of type $coll underlying this `TraversableLike` object.
   112      *  By default this is implemented as the `TraversableLike` object itself,
   113      *  but this can be overridden.
   114      */
   115     def repr: Repr = this.asInstanceOf[Repr]
   116 
   117     /** The underlying collection seen as an instance of `$Coll`.
   118      *  By default this is implemented as the current collection object itself,
   119      *  but this can be overridden.
   120      */
   121     protected[this] def thisCollection: Traversable[A] = this.asInstanceOf[Traversable[A]]
   122 
   123     /** A conversion from collections of type `Repr` to `$Coll` objects.
   124      *  By default this is implemented as just a cast, but this can be overridden.
   125      */
   126     protected[this] def toCollection(repr: Repr): Traversable[A] = repr.asInstanceOf[Traversable[A]]
   127 
   128     /** Creates a new builder for this collection type.
   129      */
   130     protected[this] def newBuilder: Builder[A, Repr]
   131 
   132     protected[this] def parCombiner = ParIterable.newCombiner[A]
   133 
   134     /** Applies a function `f` to all elements of this $coll.
   135      *  
   136      *    Note: this method underlies the implementation of most other bulk operations.
   137      *    It's important to implement this method in an efficient way.
   138      *  
   139      *
   140      *  @param  f   the function that is applied for its side-effect to every element.
   141      *              The result of function `f` is discarded.
   142      *              
   143      *  @tparam  U  the type parameter describing the result of function `f`. 
   144      *              This result will always be ignored. Typically `U` is `Unit`,
   145      *              but this is not necessary.
   146      *
   147      *  @usecase def foreach(f: A => Unit): Unit
   148      */
   149     def foreach[U](f: A => U): Unit
   150 
   151     /** Tests whether this $coll is empty.
   152      *
   153      *  @return    `true` if the $coll contain no elements, `false` otherwise.
   154      */
   155     def isEmpty: Boolean = {
   156       var result = true
   157       breakable {
   158         for (x <- this) {
   159           result = false
   160           break
   161         }
   162       }
   163       result
   164     }
   165 
   166     /** Tests whether this $coll is known to have a finite size.
   167      *  All strict collections are known to have finite size. For a non-strict collection
   168      *  such as `Stream`, the predicate returns `true` if all elements have been computed.
   169      *  It returns `false` if the stream is not yet evaluated to the end.
   170      *
   171      *  Note: many collection methods will not work on collections of infinite sizes. 
   172      *
   173      *  @return  `true` if this collection is known to have finite size, `false` otherwise.
   174      */
   175     def hasDefiniteSize = true
   176 
   177     def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   178       val b = bf(repr)
   179       if (that.isInstanceOf[IndexedSeqLike[_, _]]) b.sizeHint(this, that.seq.size)
   180       b ++= thisCollection
   181       b ++= that.seq
   182       b.result
   183     }
   184 
   185     @bridge
   186     def ++[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That =
   187       ++(that: GenTraversableOnce[B])(bf)
   188 
   189     /** Concatenates this $coll with the elements of a traversable collection.
   190      *  It differs from ++ in that the right operand determines the type of the
   191      *  resulting collection rather than the left one.
   192      * 
   193      *  @param that   the traversable to append.
   194      *  @tparam B     the element type of the returned collection. 
   195      *  @tparam That  $thatinfo
   196      *  @param bf     $bfinfo
   197      *  @return       a new collection of type `That` which contains all elements
   198      *                of this $coll followed by all elements of `that`.
   199      * 
   200      *  @usecase def ++:[B](that: TraversableOnce[B]): $Coll[B]
   201      *  
   202      *  @return       a new $coll which contains all elements of this $coll
   203      *                followed by all elements of `that`.
   204      */
   205     def ++:[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   206       val b = bf(repr)
   207       if (that.isInstanceOf[IndexedSeqLike[_, _]]) b.sizeHint(this, that.size)
   208       b ++= that
   209       b ++= thisCollection
   210       b.result
   211     }
   212 
   213     /** This overload exists because: for the implementation of ++: we should reuse
   214      *  that of ++ because many collections override it with more efficient versions.
   215      *  Since TraversableOnce has no '++' method, we have to implement that directly,
   216      *  but Traversable and down can use the overload.
   217      */
   218     def ++:[B >: A, That](that: Traversable[B])(implicit bf: CanBuildFrom[Repr, B, That]): That =
   219       (that ++ seq)(breakOut)
   220 
   221     def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   222       val b = bf(repr)
   223       b.sizeHint(this) 
   224       for (x <- this) b += f(x)
   225       b.result
   226     }
   227 
   228     def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   229       val b = bf(repr)
   230       for (x <- this) b ++= f(x).seq
   231       b.result
   232     }
   233 
   234     /** Selects all elements of this $coll which satisfy a predicate.
   235      *
   236      *  @param p     the predicate used to test elements.
   237      *  @return      a new $coll consisting of all elements of this $coll that satisfy the given
   238      *               predicate `p`. The order of the elements is preserved.
   239      */
   240     def filter(p: A => Boolean): Repr = {
   241       val b = newBuilder
   242       for (x <- this) 
   243         if (p(x)) b += x
   244       b.result
   245     }
   246 
   247     /** Selects all elements of this $coll which do not satisfy a predicate.
   248      *
   249      *  @param p     the predicate used to test elements.
   250      *  @return      a new $coll consisting of all elements of this $coll that do not satisfy the given
   251      *               predicate `p`. The order of the elements is preserved.
   252      */
   253     def filterNot(p: A => Boolean): Repr = filter(!p(_))
   254 
   255     def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   256       val b = bf(repr)
   257       for (x <- this) if (pf.isDefinedAt(x)) b += pf(x)
   258       b.result
   259     }
   260 
   261     /** Builds a new collection by applying an option-valued function to all
   262      *  elements of this $coll on which the function is defined.
   263      *
   264      *  @param f      the option-valued function which filters and maps the $coll.
   265      *  @tparam B     the element type of the returned collection.
   266      *  @tparam That  $thatinfo
   267      *  @param bf     $bfinfo
   268      *  @return       a new collection of type `That` resulting from applying the option-valued function
   269      *                `f` to each element and collecting all defined results.
   270      *                The order of the elements is preserved.
   271      *
   272      *  @usecase def filterMap[B](f: A => Option[B]): $Coll[B]
   273      *  
   274      *  @param pf     the partial function which filters and maps the $coll.
   275      *  @return       a new $coll resulting from applying the given option-valued function
   276      *                `f` to each element and collecting all defined results.
   277      *                The order of the elements is preserved.
   278     def filterMap[B, That](f: A => Option[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   279       val b = bf(repr)
   280       for (x <- this) 
   281         f(x) match {
   282           case Some(y) => b += y
   283           case _ =>
   284         }
   285       b.result
   286     }
   287      */
   288 
   289     /** Partitions this $coll in two ${coll}s according to a predicate.
   290      *
   291      *  @param p the predicate on which to partition.
   292      *  @return  a pair of ${coll}s: the first $coll consists of all elements that 
   293      *           satisfy the predicate `p` and the second $coll consists of all elements
   294      *           that don't. The relative order of the elements in the resulting ${coll}s
   295      *           is the same as in the original $coll.
   296      */
   297     def partition(p: A => Boolean): (Repr, Repr) = {
   298       val l, r = newBuilder
   299       for (x <- this) (if (p(x)) l else r) += x
   300       (l.result, r.result)
   301     }
   302 
   303     def groupBy[K](f: A => K): immutable.Map[K, Repr] = {
   304       val m = mutable.Map.empty[K, Builder[A, Repr]]
   305       for (elem <- this) {
   306         val key = f(elem)
   307         val bldr = m.getOrElseUpdate(key, newBuilder)
   308         bldr += elem
   309       }
   310       val b = immutable.Map.newBuilder[K, Repr]
   311       for ((k, v) <- m)
   312         b += ((k, v.result))
   313 
   314       b.result
   315     }
   316 
   317     /** Tests whether a predicate holds for all elements of this $coll.
   318      *
   319      *  $mayNotTerminateInf
   320      *
   321      *  @param   p     the predicate used to test elements.
   322      *  @return        `true` if the given predicate `p` holds for all elements
   323      *                 of this $coll, otherwise `false`.
   324      */
   325     def forall(p: A => Boolean): Boolean = {
   326       var result = true
   327       breakable {
   328         for (x <- this)
   329           if (!p(x)) { result = false; break }
   330       }
   331       result
   332     }
   333 
   334     /** Tests whether a predicate holds for some of the elements of this $coll.
   335      *
   336      *  $mayNotTerminateInf
   337      *
   338      *  @param   p     the predicate used to test elements.
   339      *  @return        `true` if the given predicate `p` holds for some of the
   340      *                 elements of this $coll, otherwise `false`.
   341      */
   342     def exists(p: A => Boolean): Boolean = {
   343       var result = false
   344       breakable {
   345         for (x <- this)
   346           if (p(x)) { result = true; break }
   347       }
   348       result
   349     }
   350 
   351     /** Finds the first element of the $coll satisfying a predicate, if any.
   352      * 
   353      *  $mayNotTerminateInf
   354      *  $orderDependent
   355      *
   356      *  @param p    the predicate used to test elements.
   357      *  @return     an option value containing the first element in the $coll
   358      *              that satisfies `p`, or `None` if none exists.
   359      */
   360     def find(p: A => Boolean): Option[A] = {
   361       var result: Option[A] = None
   362       breakable {
   363         for (x <- this)
   364           if (p(x)) { result = Some(x); break }
   365       }
   366       result
   367     }
   368 
   369     def scan[B >: A, That](z: B)(op: (B, B) => B)(implicit cbf: CanBuildFrom[Repr, B, That]): That = scanLeft(z)(op)
   370 
   371     def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   372       val b = bf(repr)
   373       b.sizeHint(this, 1)
   374       var acc = z
   375       b += acc
   376       for (x <- this) { acc = op(acc, x); b += acc }
   377       b.result
   378     }
   379 
   380     @migration(2, 9,
   381       "This scanRight definition has changed in 2.9.\n" +
   382       "The previous behavior can be reproduced with scanRight.reverse."
   383     )
   384     def scanRight[B, That](z: B)(op: (A, B) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   385       var scanned = List(z)
   386       var acc = z
   387       for (x <- reversed) {
   388         acc = op(x, acc)
   389         scanned ::= acc
   390       }
   391       val b = bf(repr)
   392       for (elem <- scanned) b += elem
   393       b.result
   394     }
   395 
   396     /** Selects the first element of this $coll.
   397      *  $orderDependent
   398      *  @return  the first element of this $coll.
   399      *  @throws `NoSuchElementException` if the $coll is empty.
   400      */
   401     def head: A = {
   402       var result: () => A = () => throw new NoSuchElementException
   403       breakable {
   404         for (x <- this) {
   405           result = () => x
   406           break
   407         }
   408       }
   409       result()
   410     }
   411 
   412     /** Optionally selects the first element.
   413      *  $orderDependent
   414      *  @return  the first element of this $coll if it is nonempty, `None` if it is empty.
   415      */
   416     def headOption: Option[A] = if (isEmpty) None else Some(head)
   417 
   418     /** Selects all elements except the first.
   419      *  $orderDependent
   420      *  @return  a $coll consisting of all elements of this $coll
   421      *           except the first one.
   422      *  @throws `UnsupportedOperationException` if the $coll is empty.
   423      */ 
   424     override def tail: Repr = {
   425       if (isEmpty) throw new UnsupportedOperationException("empty.tail")
   426       drop(1)
   427     }
   428 
   429     /** Selects the last element.
   430       * $orderDependent
   431       * @return The last element of this $coll.
   432       * @throws NoSuchElementException If the $coll is empty.
   433       */
   434     def last: A = {
   435       var lst = head
   436       for (x <- this)
   437         lst = x
   438       lst
   439     }
   440 
   441     /** Optionally selects the last element.
   442      *  $orderDependent
   443      *  @return  the last element of this $coll$ if it is nonempty, `None` if it is empty.
   444      */
   445     def lastOption: Option[A] = if (isEmpty) None else Some(last)
   446 
   447     /** Selects all elements except the last.
   448      *  $orderDependent
   449      *  @return  a $coll consisting of all elements of this $coll
   450      *           except the last one.
   451      *  @throws `UnsupportedOperationException` if the $coll is empty.
   452      */
   453     def init: Repr = {
   454       if (isEmpty) throw new UnsupportedOperationException("empty.init")
   455       var lst = head
   456       var follow = false
   457       val b = newBuilder
   458       b.sizeHint(this, -1)
   459       for (x <- this.seq) {
   460         if (follow) b += lst
   461         else follow = true
   462         lst = x
   463       }
   464       b.result
   465     }
   466 
   467     def take(n: Int): Repr = slice(0, n)
   468 
   469     def drop(n: Int): Repr = 
   470       if (n <= 0) {
   471         val b = newBuilder
   472         b.sizeHint(this)
   473         b ++= thisCollection result
   474       }
   475       else sliceWithKnownDelta(n, Int.MaxValue, -n)
   476 
   477     def slice(from: Int, until: Int): Repr = sliceWithKnownBound(math.max(from, 0), until)
   478 
   479     // Precondition: from >= 0, until > 0, builder already configured for building.
   480     private[this] def sliceInternal(from: Int, until: Int, b: Builder[A, Repr]): Repr = {
   481       var i = 0
   482       breakable {
   483         for (x <- this.seq) {
   484           if (i >= from) b += x
   485           i += 1
   486           if (i >= until) break
   487         }
   488       }
   489       b.result
   490     }
   491     // Precondition: from >= 0
   492     private[scala] def sliceWithKnownDelta(from: Int, until: Int, delta: Int): Repr = {
   493       val b = newBuilder
   494       if (until <= from) b.result
   495       else {
   496         b.sizeHint(this, delta)
   497         sliceInternal(from, until, b)
   498       }
   499     }
   500     // Precondition: from >= 0
   501     private[scala] def sliceWithKnownBound(from: Int, until: Int): Repr = {
   502       val b = newBuilder
   503       if (until <= from) b.result
   504       else {
   505         b.sizeHintBounded(until - from, this)      
   506         sliceInternal(from, until, b)
   507       }
   508     }
   509 
   510     def takeWhile(p: A => Boolean): Repr = {
   511       val b = newBuilder
   512       breakable {
   513         for (x <- this) {
   514           if (!p(x)) break
   515           b += x
   516         }
   517       }
   518       b.result
   519     }
   520 
   521     def dropWhile(p: A => Boolean): Repr = {
   522       val b = newBuilder
   523       var go = false
   524       for (x <- this) {
   525         if (!p(x)) go = true
   526         if (go) b += x
   527       }
   528       b.result
   529     }
   530 
   531     def span(p: A => Boolean): (Repr, Repr) = {
   532       val l, r = newBuilder
   533       var toLeft = true
   534       for (x <- this) {
   535         toLeft = toLeft && p(x)
   536         (if (toLeft) l else r) += x
   537       }
   538       (l.result, r.result)
   539     }
   540 
   541     def splitAt(n: Int): (Repr, Repr) = {
   542       val l, r = newBuilder
   543       l.sizeHintBounded(n, this)
   544       if (n >= 0) r.sizeHint(this, -n)
   545       var i = 0
   546       for (x <- this) {
   547         (if (i < n) l else r) += x
   548         i += 1
   549       }
   550       (l.result, r.result)
   551     }
   552 
   553     /** Iterates over the tails of this $coll. The first value will be this
   554      *  $coll and the final one will be an empty $coll, with the intervening
   555      *  values the results of successive applications of `tail`.
   556      *
   557      *  @return   an iterator over all the tails of this $coll
   558      *  @example  `List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)`
   559      */  
   560     def tails: Iterator[Repr] = iterateUntilEmpty(_.tail)
   561 
   562     /** Iterates over the inits of this $coll. The first value will be this
   563      *  $coll and the final one will be an empty $coll, with the intervening
   564      *  values the results of successive applications of `init`.
   565      *
   566      *  @return  an iterator over all the inits of this $coll
   567      *  @example  `List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)`
   568      */
   569     def inits: Iterator[Repr] = iterateUntilEmpty(_.init)
   570 
   571     /** Copies elements of this $coll to an array.
   572      *  Fills the given array `xs` with at most `len` elements of
   573      *  this $coll, starting at position `start`.
   574      *  Copying will stop once either the end of the current $coll is reached,
   575      *  or the end of the array is reached, or `len` elements have been copied.
   576      *
   577      *  $willNotTerminateInf
   578      * 
   579      *  @param  xs     the array to fill.
   580      *  @param  start  the starting index.
   581      *  @param  len    the maximal number of elements to copy.
   582      *  @tparam B      the type of the elements of the array. 
   583      * 
   584      *
   585      *  @usecase def copyToArray(xs: Array[A], start: Int, len: Int): Unit
   586      */
   587     def copyToArray[B >: A](xs: Array[B], start: Int, len: Int) {
   588       var i = start
   589       val end = (start + len) min xs.length
   590       breakable {
   591         for (x <- this) {
   592           if (i >= end) break
   593           xs(i) = x
   594           i += 1
   595         }
   596       }
   597     }
   598 
   599     def toTraversable: Traversable[A] = thisCollection
   600     def toIterator: Iterator[A] = toStream.iterator
   601     def toStream: Stream[A] = toBuffer.toStream
   602 
   603     /** Converts this $coll to a string.
   604      *
   605      *  @return   a string representation of this collection. By default this
   606      *            string consists of the `stringPrefix` of this $coll,
   607      *            followed by all elements separated by commas and enclosed in parentheses.
   608      */
   609     override def toString = mkString(stringPrefix + "(", ", ", ")")
   610 
   611     /** Defines the prefix of this object's `toString` representation.
   612      *
   613      *  @return  a string representation which starts the result of `toString`
   614      *           applied to this $coll. By default the string prefix is the
   615      *           simple name of the collection class $coll.
   616      */
   617     def stringPrefix : String = {
   618       var string = repr.asInstanceOf[AnyRef].getClass.getName
   619       val idx1 = string.lastIndexOf('.' : Int)
   620       if (idx1 != -1) string = string.substring(idx1 + 1)
   621       val idx2 = string.indexOf('$')
   622       if (idx2 != -1) string = string.substring(0, idx2)
   623       string
   624     }
   625 
   626     /** Creates a non-strict view of this $coll.
   627      * 
   628      *  @return a non-strict view of this $coll.
   629      */
   630     def view = new TraversableView[A, Repr] {
   631       protected lazy val underlying = self.repr
   632       override def foreach[U](f: A => U) = self foreach f
   633     }
   634 
   635     /** Creates a non-strict view of a slice of this $coll.
   636      *
   637      *  Note: the difference between `view` and `slice` is that `view` produces
   638      *        a view of the current $coll, whereas `slice` produces a new $coll.
   639      * 
   640      *  Note: `view(from, to)` is equivalent to `view.slice(from, to)`
   641      *  $orderDependent
   642      * 
   643      *  @param from   the index of the first element of the view
   644      *  @param until  the index of the element following the view
   645      *  @return a non-strict view of a slice of this $coll, starting at index `from`
   646      *  and extending up to (but not including) index `until`.
   647      */
   648     def view(from: Int, until: Int): TraversableView[A, Repr] = view.slice(from, until)
   649 
   650     /** Creates a non-strict filter of this $coll.
   651      *
   652      *  Note: the difference between `c filter p` and `c withFilter p` is that
   653      *        the former creates a new collection, whereas the latter only
   654      *        restricts the domain of subsequent `map`, `flatMap`, `foreach`,
   655      *        and `withFilter` operations.
   656      *  $orderDependent
   657      * 
   658      *  @param p   the predicate used to test elements.
   659      *  @return    an object of class `WithFilter`, which supports
   660      *             `map`, `flatMap`, `foreach`, and `withFilter` operations.
   661      *             All these operations apply to those elements of this $coll which
   662      *             satisfy the predicate `p`.
   663      */
   664     def withFilter(p: A => Boolean): FilterMonadic[A, Repr] = new WithFilter(p)
   665 
   666     /** A class supporting filtered operations. Instances of this class are
   667      *  returned by method `withFilter`.
   668      */
   669     class WithFilter(p: A => Boolean) extends FilterMonadic[A, Repr] {
   670 
   671       /** Builds a new collection by applying a function to all elements of the
   672        *  outer $coll containing this `WithFilter` instance that satisfy predicate `p`.
   673        *
   674        *  @param f      the function to apply to each element.
   675        *  @tparam B     the element type of the returned collection.
   676        *  @tparam That  $thatinfo
   677        *  @param bf     $bfinfo
   678        *  @return       a new collection of type `That` resulting from applying
   679        *                the given function `f` to each element of the outer $coll
   680        *                that satisfies predicate `p` and collecting the results.
   681        *
   682        *  @usecase def map[B](f: A => B): $Coll[B] 
   683        *  
   684        *  @return       a new $coll resulting from applying the given function
   685        *                `f` to each element of the outer $coll that satisfies
   686        *                predicate `p` and collecting the results.
   687        */
   688       def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   689         val b = bf(repr)
   690         for (x <- self) 
   691           if (p(x)) b += f(x)
   692         b.result
   693       }
   694 
   695       /** Builds a new collection by applying a function to all elements of the
   696        *  outer $coll containing this `WithFilter` instance that satisfy
   697        *  predicate `p` and concatenating the results. 
   698        *
   699        *  @param f      the function to apply to each element.
   700        *  @tparam B     the element type of the returned collection.
   701        *  @tparam That  $thatinfo
   702        *  @param bf     $bfinfo
   703        *  @return       a new collection of type `That` resulting from applying
   704        *                the given collection-valued function `f` to each element
   705        *                of the outer $coll that satisfies predicate `p` and
   706        *                concatenating the results.
   707        *
   708        *  @usecase def flatMap[B](f: A => TraversableOnce[B]): $Coll[B]
   709        * 
   710        *  @return       a new $coll resulting from applying the given collection-valued function
   711        *                `f` to each element of the outer $coll that satisfies predicate `p` and concatenating the results.
   712        */
   713       def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
   714         val b = bf(repr)
   715         for (x <- self) 
   716           if (p(x)) b ++= f(x).seq
   717         b.result
   718       }
   719 
   720       /** Applies a function `f` to all elements of the outer $coll containing
   721        *  this `WithFilter` instance that satisfy predicate `p`.
   722        *
   723        *  @param  f   the function that is applied for its side-effect to every element.
   724        *              The result of function `f` is discarded.
   725        *              
   726        *  @tparam  U  the type parameter describing the result of function `f`. 
   727        *              This result will always be ignored. Typically `U` is `Unit`,
   728        *              but this is not necessary.
   729        *
   730        *  @usecase def foreach(f: A => Unit): Unit
   731        */   
   732       def foreach[U](f: A => U): Unit = 
   733         for (x <- self) 
   734           if (p(x)) f(x)
   735 
   736       /** Further refines the filter for this $coll.
   737        *
   738        *  @param q   the predicate used to test elements.
   739        *  @return    an object of class `WithFilter`, which supports
   740        *             `map`, `flatMap`, `foreach`, and `withFilter` operations.
   741        *             All these operations apply to those elements of this $coll which
   742        *             satisfy the predicate `q` in addition to the predicate `p`.
   743        */
   744       def withFilter(q: A => Boolean): WithFilter = 
   745         new WithFilter(x => p(x) && q(x))
   746     }
   747 
   748     // A helper for tails and inits.
   749     private def iterateUntilEmpty(f: Traversable[A @uV] => Traversable[A @uV]): Iterator[Repr] = {
   750       val it = Iterator.iterate(thisCollection)(f) takeWhile (x => !x.isEmpty)
   751       it ++ Iterator(Nil) map (newBuilder ++= _ result)
   752     }
   753   }
   754 
   755 
   756 </textarea>
   757 </form>
   758 
   759     <script>
   760       var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
   761         lineNumbers: true,
   762         matchBrackets: true,
   763         theme: "ambiance",
   764         mode: "text/x-scala"
   765       });
   766     </script>
   767   </article>



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History
Sun, 17 Dec 2017 01:14:09 +0100	Jan Dankert	Integration eines weiteren Code-Editors: Codemirror. Demnächst müssen wir hier mal aufräumen und andere Editoren rauswerfen.