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/* __ *\ | ||||
** ________ ___ / / ___ Scala API ** | ||||
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL ** | ||||
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ ** | ||||
** /____/\___/_/ |_/____/_/ | | ** | ||||
** |/ ** | ||||
\* */ | ||||
package scala.collection | ||||
import generic._ | ||||
import mutable.{ Builder, ListBuffer } | ||||
import annotation.{tailrec, migration, bridge} | ||||
import annotation.unchecked.{ uncheckedVariance => uV } | ||||
import parallel.ParIterable | ||||
/** A template trait for traversable collections of type `Traversable[A]`. | ||||
* | ||||
* $traversableInfo | ||||
* @define mutability | ||||
* @define traversableInfo | ||||
* This is a base trait of all kinds of $mutability Scala collections. It | ||||
* implements the behavior common to all collections, in terms of a method | ||||
* `foreach` with signature: | ||||
* {{{ | ||||
* def foreach[U](f: Elem => U): Unit | ||||
* }}} | ||||
* Collection classes mixing in this trait provide a concrete | ||||
* `foreach` method which traverses all the | ||||
* elements contained in the collection, applying a given function to each. | ||||
* They also need to provide a method `newBuilder` | ||||
* which creates a builder for collections of the same kind. | ||||
* | ||||
* A traversable class might or might not have two properties: strictness | ||||
* and orderedness. Neither is represented as a type. | ||||
* | ||||
* The instances of a strict collection class have all their elements | ||||
* computed before they can be used as values. By contrast, instances of | ||||
* a non-strict collection class may defer computation of some of their | ||||
* elements until after the instance is available as a value. | ||||
* A typical example of a non-strict collection class is a | ||||
* <a href="../immutable/Stream.html" target="ContentFrame"> | ||||
* `scala.collection.immutable.Stream`</a>. | ||||
* A more general class of examples are `TraversableViews`. | ||||
* | ||||
* If a collection is an instance of an ordered collection class, traversing | ||||
* its elements with `foreach` will always visit elements in the | ||||
* same order, even for different runs of the program. If the class is not | ||||
* ordered, `foreach` can visit elements in different orders for | ||||
* different runs (but it will keep the same order in the same run).' | ||||
* | ||||
* A typical example of a collection class which is not ordered is a | ||||
* `HashMap` of objects. The traversal order for hash maps will | ||||
* depend on the hash codes of its elements, and these hash codes might | ||||
* differ from one run to the next. By contrast, a `LinkedHashMap` | ||||
* is ordered because it's `foreach` method visits elements in the | ||||
* order they were inserted into the `HashMap`. | ||||
* | ||||
* @author Martin Odersky | ||||
* @version 2.8 | ||||
* @since 2.8 | ||||
* @tparam A the element type of the collection | ||||
* @tparam Repr the type of the actual collection containing the elements. | ||||
* | ||||
* @define Coll Traversable | ||||
* @define coll traversable collection | ||||
*/ | ||||
trait TraversableLike[+A, +Repr] extends HasNewBuilder[A, Repr] | ||||
with FilterMonadic[A, Repr] | ||||
with TraversableOnce[A] | ||||
with GenTraversableLike[A, Repr] | ||||
with Parallelizable[A, ParIterable[A]] | ||||
{ | ||||
self => | ||||
import Traversable.breaks._ | ||||
/** The type implementing this traversable */ | ||||
protected type Self = Repr | ||||
/** The collection of type $coll underlying this `TraversableLike` object. | ||||
* By default this is implemented as the `TraversableLike` object itself, | ||||
* but this can be overridden. | ||||
*/ | ||||
def repr: Repr = this.asInstanceOf[Repr] | ||||
/** The underlying collection seen as an instance of `$Coll`. | ||||
* By default this is implemented as the current collection object itself, | ||||
* but this can be overridden. | ||||
*/ | ||||
protected[this] def thisCollection: Traversable[A] = this.asInstanceOf[Traversable[A]] | ||||
/** A conversion from collections of type `Repr` to `$Coll` objects. | ||||
* By default this is implemented as just a cast, but this can be overridden. | ||||
*/ | ||||
protected[this] def toCollection(repr: Repr): Traversable[A] = repr.asInstanceOf[Traversable[A]] | ||||
/** Creates a new builder for this collection type. | ||||
*/ | ||||
protected[this] def newBuilder: Builder[A, Repr] | ||||
protected[this] def parCombiner = ParIterable.newCombiner[A] | ||||
/** Applies a function `f` to all elements of this $coll. | ||||
* | ||||
* Note: this method underlies the implementation of most other bulk operations. | ||||
* It's important to implement this method in an efficient way. | ||||
* | ||||
* | ||||
* @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 | ||||
/** Tests whether this $coll is empty. | ||||
* | ||||
* @return `true` if the $coll contain no elements, `false` otherwise. | ||||
*/ | ||||
def isEmpty: Boolean = { | ||||
var result = true | ||||
breakable { | ||||
for (x <- this) { | ||||
result = false | ||||
break | ||||
} | ||||
} | ||||
result | ||||
} | ||||
/** Tests whether this $coll is known to have a finite size. | ||||
* All strict collections are known to have finite size. For a non-strict collection | ||||
* such as `Stream`, the predicate returns `true` if all elements have been computed. | ||||
* It returns `false` if the stream is not yet evaluated to the end. | ||||
* | ||||
* Note: many collection methods will not work on collections of infinite sizes. | ||||
* | ||||
* @return `true` if this collection is known to have finite size, `false` otherwise. | ||||
*/ | ||||
def hasDefiniteSize = true | ||||
def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
if (that.isInstanceOf[IndexedSeqLike[_, _]]) b.sizeHint(this, that.seq.size) | ||||
b ++= thisCollection | ||||
b ++= that.seq | ||||
b.result | ||||
} | ||||
@bridge | ||||
def ++[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = | ||||
++(that: GenTraversableOnce[B])(bf) | ||||
/** Concatenates this $coll with the elements of a traversable collection. | ||||
* It differs from ++ in that the right operand determines the type of the | ||||
* resulting collection rather than the left one. | ||||
* | ||||
* @param that the traversable to append. | ||||
* @tparam B the element type of the returned collection. | ||||
* @tparam That $thatinfo | ||||
* @param bf $bfinfo | ||||
* @return a new collection of type `That` which contains all elements | ||||
* of this $coll followed by all elements of `that`. | ||||
* | ||||
* @usecase def ++:[B](that: TraversableOnce[B]): $Coll[B] | ||||
* | ||||
* @return a new $coll which contains all elements of this $coll | ||||
* followed by all elements of `that`. | ||||
*/ | ||||
def ++:[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
if (that.isInstanceOf[IndexedSeqLike[_, _]]) b.sizeHint(this, that.size) | ||||
b ++= that | ||||
b ++= thisCollection | ||||
b.result | ||||
} | ||||
/** This overload exists because: for the implementation of ++: we should reuse | ||||
* that of ++ because many collections override it with more efficient versions. | ||||
* Since TraversableOnce has no '++' method, we have to implement that directly, | ||||
* but Traversable and down can use the overload. | ||||
*/ | ||||
def ++:[B >: A, That](that: Traversable[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = | ||||
(that ++ seq)(breakOut) | ||||
def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
b.sizeHint(this) | ||||
for (x <- this) b += f(x) | ||||
b.result | ||||
} | ||||
def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
for (x <- this) b ++= f(x).seq | ||||
b.result | ||||
} | ||||
/** Selects all elements of this $coll which satisfy a predicate. | ||||
* | ||||
* @param p the predicate used to test elements. | ||||
* @return a new $coll consisting of all elements of this $coll that satisfy the given | ||||
* predicate `p`. The order of the elements is preserved. | ||||
*/ | ||||
def filter(p: A => Boolean): Repr = { | ||||
val b = newBuilder | ||||
for (x <- this) | ||||
if (p(x)) b += x | ||||
b.result | ||||
} | ||||
/** Selects all elements of this $coll which do not satisfy a predicate. | ||||
* | ||||
* @param p the predicate used to test elements. | ||||
* @return a new $coll consisting of all elements of this $coll that do not satisfy the given | ||||
* predicate `p`. The order of the elements is preserved. | ||||
*/ | ||||
def filterNot(p: A => Boolean): Repr = filter(!p(_)) | ||||
def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
for (x <- this) if (pf.isDefinedAt(x)) b += pf(x) | ||||
b.result | ||||
} | ||||
/** Builds a new collection by applying an option-valued function to all | ||||
* elements of this $coll on which the function is defined. | ||||
* | ||||
* @param f the option-valued function which filters and maps the $coll. | ||||
* @tparam B the element type of the returned collection. | ||||
* @tparam That $thatinfo | ||||
* @param bf $bfinfo | ||||
* @return a new collection of type `That` resulting from applying the option-valued function | ||||
* `f` to each element and collecting all defined results. | ||||
* The order of the elements is preserved. | ||||
* | ||||
* @usecase def filterMap[B](f: A => Option[B]): $Coll[B] | ||||
* | ||||
* @param pf the partial function which filters and maps the $coll. | ||||
* @return a new $coll resulting from applying the given option-valued function | ||||
* `f` to each element and collecting all defined results. | ||||
* The order of the elements is preserved. | ||||
def filterMap[B, That](f: A => Option[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
for (x <- this) | ||||
f(x) match { | ||||
case Some(y) => b += y | ||||
case _ => | ||||
} | ||||
b.result | ||||
} | ||||
*/ | ||||
/** Partitions this $coll in two ${coll}s according to a predicate. | ||||
* | ||||
* @param p the predicate on which to partition. | ||||
* @return a pair of ${coll}s: the first $coll consists of all elements that | ||||
* satisfy the predicate `p` and the second $coll consists of all elements | ||||
* that don't. The relative order of the elements in the resulting ${coll}s | ||||
* is the same as in the original $coll. | ||||
*/ | ||||
def partition(p: A => Boolean): (Repr, Repr) = { | ||||
val l, r = newBuilder | ||||
for (x <- this) (if (p(x)) l else r) += x | ||||
(l.result, r.result) | ||||
} | ||||
def groupBy[K](f: A => K): immutable.Map[K, Repr] = { | ||||
val m = mutable.Map.empty[K, Builder[A, Repr]] | ||||
for (elem <- this) { | ||||
val key = f(elem) | ||||
val bldr = m.getOrElseUpdate(key, newBuilder) | ||||
bldr += elem | ||||
} | ||||
val b = immutable.Map.newBuilder[K, Repr] | ||||
for ((k, v) <- m) | ||||
b += ((k, v.result)) | ||||
b.result | ||||
} | ||||
/** Tests whether a predicate holds for all elements of this $coll. | ||||
* | ||||
* $mayNotTerminateInf | ||||
* | ||||
* @param p the predicate used to test elements. | ||||
* @return `true` if the given predicate `p` holds for all elements | ||||
* of this $coll, otherwise `false`. | ||||
*/ | ||||
def forall(p: A => Boolean): Boolean = { | ||||
var result = true | ||||
breakable { | ||||
for (x <- this) | ||||
if (!p(x)) { result = false; break } | ||||
} | ||||
result | ||||
} | ||||
/** Tests whether a predicate holds for some of the elements of this $coll. | ||||
* | ||||
* $mayNotTerminateInf | ||||
* | ||||
* @param p the predicate used to test elements. | ||||
* @return `true` if the given predicate `p` holds for some of the | ||||
* elements of this $coll, otherwise `false`. | ||||
*/ | ||||
def exists(p: A => Boolean): Boolean = { | ||||
var result = false | ||||
breakable { | ||||
for (x <- this) | ||||
if (p(x)) { result = true; break } | ||||
} | ||||
result | ||||
} | ||||
/** Finds the first element of the $coll satisfying a predicate, if any. | ||||
* | ||||
* $mayNotTerminateInf | ||||
* $orderDependent | ||||
* | ||||
* @param p the predicate used to test elements. | ||||
* @return an option value containing the first element in the $coll | ||||
* that satisfies `p`, or `None` if none exists. | ||||
*/ | ||||
def find(p: A => Boolean): Option[A] = { | ||||
var result: Option[A] = None | ||||
breakable { | ||||
for (x <- this) | ||||
if (p(x)) { result = Some(x); break } | ||||
} | ||||
result | ||||
} | ||||
def scan[B >: A, That](z: B)(op: (B, B) => B)(implicit cbf: CanBuildFrom[Repr, B, That]): That = scanLeft(z)(op) | ||||
def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
b.sizeHint(this, 1) | ||||
var acc = z | ||||
b += acc | ||||
for (x <- this) { acc = op(acc, x); b += acc } | ||||
b.result | ||||
} | ||||
@migration(2, 9, | ||||
"This scanRight definition has changed in 2.9.\n" + | ||||
"The previous behavior can be reproduced with scanRight.reverse." | ||||
) | ||||
def scanRight[B, That](z: B)(op: (A, B) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
var scanned = List(z) | ||||
var acc = z | ||||
for (x <- reversed) { | ||||
acc = op(x, acc) | ||||
scanned ::= acc | ||||
} | ||||
val b = bf(repr) | ||||
for (elem <- scanned) b += elem | ||||
b.result | ||||
} | ||||
/** Selects the first element of this $coll. | ||||
* $orderDependent | ||||
* @return the first element of this $coll. | ||||
* @throws `NoSuchElementException` if the $coll is empty. | ||||
*/ | ||||
def head: A = { | ||||
var result: () => A = () => throw new NoSuchElementException | ||||
breakable { | ||||
for (x <- this) { | ||||
result = () => x | ||||
break | ||||
} | ||||
} | ||||
result() | ||||
} | ||||
/** Optionally selects the first element. | ||||
* $orderDependent | ||||
* @return the first element of this $coll if it is nonempty, `None` if it is empty. | ||||
*/ | ||||
def headOption: Option[A] = if (isEmpty) None else Some(head) | ||||
/** Selects all elements except the first. | ||||
* $orderDependent | ||||
* @return a $coll consisting of all elements of this $coll | ||||
* except the first one. | ||||
* @throws `UnsupportedOperationException` if the $coll is empty. | ||||
*/ | ||||
override def tail: Repr = { | ||||
if (isEmpty) throw new UnsupportedOperationException("empty.tail") | ||||
drop(1) | ||||
} | ||||
/** Selects the last element. | ||||
* $orderDependent | ||||
* @return The last element of this $coll. | ||||
* @throws NoSuchElementException If the $coll is empty. | ||||
*/ | ||||
def last: A = { | ||||
var lst = head | ||||
for (x <- this) | ||||
lst = x | ||||
lst | ||||
} | ||||
/** Optionally selects the last element. | ||||
* $orderDependent | ||||
* @return the last element of this $coll$ if it is nonempty, `None` if it is empty. | ||||
*/ | ||||
def lastOption: Option[A] = if (isEmpty) None else Some(last) | ||||
/** Selects all elements except the last. | ||||
* $orderDependent | ||||
* @return a $coll consisting of all elements of this $coll | ||||
* except the last one. | ||||
* @throws `UnsupportedOperationException` if the $coll is empty. | ||||
*/ | ||||
def init: Repr = { | ||||
if (isEmpty) throw new UnsupportedOperationException("empty.init") | ||||
var lst = head | ||||
var follow = false | ||||
val b = newBuilder | ||||
b.sizeHint(this, -1) | ||||
for (x <- this.seq) { | ||||
if (follow) b += lst | ||||
else follow = true | ||||
lst = x | ||||
} | ||||
b.result | ||||
} | ||||
def take(n: Int): Repr = slice(0, n) | ||||
def drop(n: Int): Repr = | ||||
if (n <= 0) { | ||||
val b = newBuilder | ||||
b.sizeHint(this) | ||||
b ++= thisCollection result | ||||
} | ||||
else sliceWithKnownDelta(n, Int.MaxValue, -n) | ||||
def slice(from: Int, until: Int): Repr = sliceWithKnownBound(math.max(from, 0), until) | ||||
// Precondition: from >= 0, until > 0, builder already configured for building. | ||||
private[this] def sliceInternal(from: Int, until: Int, b: Builder[A, Repr]): Repr = { | ||||
var i = 0 | ||||
breakable { | ||||
for (x <- this.seq) { | ||||
if (i >= from) b += x | ||||
i += 1 | ||||
if (i >= until) break | ||||
} | ||||
} | ||||
b.result | ||||
} | ||||
// Precondition: from >= 0 | ||||
private[scala] def sliceWithKnownDelta(from: Int, until: Int, delta: Int): Repr = { | ||||
val b = newBuilder | ||||
if (until <= from) b.result | ||||
else { | ||||
b.sizeHint(this, delta) | ||||
sliceInternal(from, until, b) | ||||
} | ||||
} | ||||
// Precondition: from >= 0 | ||||
private[scala] def sliceWithKnownBound(from: Int, until: Int): Repr = { | ||||
val b = newBuilder | ||||
if (until <= from) b.result | ||||
else { | ||||
b.sizeHintBounded(until - from, this) | ||||
sliceInternal(from, until, b) | ||||
} | ||||
} | ||||
def takeWhile(p: A => Boolean): Repr = { | ||||
val b = newBuilder | ||||
breakable { | ||||
for (x <- this) { | ||||
if (!p(x)) break | ||||
b += x | ||||
} | ||||
} | ||||
b.result | ||||
} | ||||
def dropWhile(p: A => Boolean): Repr = { | ||||
val b = newBuilder | ||||
var go = false | ||||
for (x <- this) { | ||||
if (!p(x)) go = true | ||||
if (go) b += x | ||||
} | ||||
b.result | ||||
} | ||||
def span(p: A => Boolean): (Repr, Repr) = { | ||||
val l, r = newBuilder | ||||
var toLeft = true | ||||
for (x <- this) { | ||||
toLeft = toLeft && p(x) | ||||
(if (toLeft) l else r) += x | ||||
} | ||||
(l.result, r.result) | ||||
} | ||||
def splitAt(n: Int): (Repr, Repr) = { | ||||
val l, r = newBuilder | ||||
l.sizeHintBounded(n, this) | ||||
if (n >= 0) r.sizeHint(this, -n) | ||||
var i = 0 | ||||
for (x <- this) { | ||||
(if (i < n) l else r) += x | ||||
i += 1 | ||||
} | ||||
(l.result, r.result) | ||||
} | ||||
/** Iterates over the tails of this $coll. The first value will be this | ||||
* $coll and the final one will be an empty $coll, with the intervening | ||||
* values the results of successive applications of `tail`. | ||||
* | ||||
* @return an iterator over all the tails of this $coll | ||||
* @example `List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)` | ||||
*/ | ||||
def tails: Iterator[Repr] = iterateUntilEmpty(_.tail) | ||||
/** Iterates over the inits of this $coll. The first value will be this | ||||
* $coll and the final one will be an empty $coll, with the intervening | ||||
* values the results of successive applications of `init`. | ||||
* | ||||
* @return an iterator over all the inits of this $coll | ||||
* @example `List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)` | ||||
*/ | ||||
def inits: Iterator[Repr] = iterateUntilEmpty(_.init) | ||||
/** Copies elements of this $coll to an array. | ||||
* Fills the given array `xs` with at most `len` elements of | ||||
* this $coll, starting at position `start`. | ||||
* Copying will stop once either the end of the current $coll is reached, | ||||
* or the end of the array is reached, or `len` elements have been copied. | ||||
* | ||||
* $willNotTerminateInf | ||||
* | ||||
* @param xs the array to fill. | ||||
* @param start the starting index. | ||||
* @param len the maximal number of elements to copy. | ||||
* @tparam B the type of the elements of the array. | ||||
* | ||||
* | ||||
* @usecase def copyToArray(xs: Array[A], start: Int, len: Int): Unit | ||||
*/ | ||||
def copyToArray[B >: A](xs: Array[B], start: Int, len: Int) { | ||||
var i = start | ||||
val end = (start + len) min xs.length | ||||
breakable { | ||||
for (x <- this) { | ||||
if (i >= end) break | ||||
xs(i) = x | ||||
i += 1 | ||||
} | ||||
} | ||||
} | ||||
def toTraversable: Traversable[A] = thisCollection | ||||
def toIterator: Iterator[A] = toStream.iterator | ||||
def toStream: Stream[A] = toBuffer.toStream | ||||
/** Converts this $coll to a string. | ||||
* | ||||
* @return a string representation of this collection. By default this | ||||
* string consists of the `stringPrefix` of this $coll, | ||||
* followed by all elements separated by commas and enclosed in parentheses. | ||||
*/ | ||||
override def toString = mkString(stringPrefix + "(", ", ", ")") | ||||
/** Defines the prefix of this object's `toString` representation. | ||||
* | ||||
* @return a string representation which starts the result of `toString` | ||||
* applied to this $coll. By default the string prefix is the | ||||
* simple name of the collection class $coll. | ||||
*/ | ||||
def stringPrefix : String = { | ||||
var string = repr.asInstanceOf[AnyRef].getClass.getName | ||||
val idx1 = string.lastIndexOf('.' : Int) | ||||
if (idx1 != -1) string = string.substring(idx1 + 1) | ||||
val idx2 = string.indexOf('$') | ||||
if (idx2 != -1) string = string.substring(0, idx2) | ||||
string | ||||
} | ||||
/** Creates a non-strict view of this $coll. | ||||
* | ||||
* @return a non-strict view of this $coll. | ||||
*/ | ||||
def view = new TraversableView[A, Repr] { | ||||
protected lazy val underlying = self.repr | ||||
override def foreach[U](f: A => U) = self foreach f | ||||
} | ||||
/** Creates a non-strict view of a slice of this $coll. | ||||
* | ||||
* Note: the difference between `view` and `slice` is that `view` produces | ||||
* a view of the current $coll, whereas `slice` produces a new $coll. | ||||
* | ||||
* Note: `view(from, to)` is equivalent to `view.slice(from, to)` | ||||
* $orderDependent | ||||
* | ||||
* @param from the index of the first element of the view | ||||
* @param until the index of the element following the view | ||||
* @return a non-strict view of a slice of this $coll, starting at index `from` | ||||
* and extending up to (but not including) index `until`. | ||||
*/ | ||||
def view(from: Int, until: Int): TraversableView[A, Repr] = view.slice(from, until) | ||||
/** Creates a non-strict filter of this $coll. | ||||
* | ||||
* Note: the difference between `c filter p` and `c withFilter p` is that | ||||
* the former creates a new collection, whereas the latter only | ||||
* restricts the domain of subsequent `map`, `flatMap`, `foreach`, | ||||
* and `withFilter` operations. | ||||
* $orderDependent | ||||
* | ||||
* @param p the predicate used to test elements. | ||||
* @return an object of class `WithFilter`, which supports | ||||
* `map`, `flatMap`, `foreach`, and `withFilter` operations. | ||||
* All these operations apply to those elements of this $coll which | ||||
* satisfy the predicate `p`. | ||||
*/ | ||||
def withFilter(p: A => Boolean): FilterMonadic[A, Repr] = new WithFilter(p) | ||||
/** A class supporting filtered operations. Instances of this class are | ||||
* returned by method `withFilter`. | ||||
*/ | ||||
class WithFilter(p: A => Boolean) extends FilterMonadic[A, Repr] { | ||||
/** Builds a new collection by applying a function to all elements of the | ||||
* outer $coll containing this `WithFilter` instance that satisfy predicate `p`. | ||||
* | ||||
* @param f the function to apply to each element. | ||||
* @tparam B the element type of the returned collection. | ||||
* @tparam That $thatinfo | ||||
* @param bf $bfinfo | ||||
* @return a new collection of type `That` resulting from applying | ||||
* the given function `f` to each element of the outer $coll | ||||
* that satisfies predicate `p` and collecting the results. | ||||
* | ||||
* @usecase def map[B](f: A => B): $Coll[B] | ||||
* | ||||
* @return a new $coll resulting from applying the given function | ||||
* `f` to each element of the outer $coll that satisfies | ||||
* predicate `p` and collecting the results. | ||||
*/ | ||||
def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
for (x <- self) | ||||
if (p(x)) b += f(x) | ||||
b.result | ||||
} | ||||
/** Builds a new collection by applying a function to all elements of the | ||||
* outer $coll containing this `WithFilter` instance that satisfy | ||||
* predicate `p` and concatenating the results. | ||||
* | ||||
* @param f the function to apply to each element. | ||||
* @tparam B the element type of the returned collection. | ||||
* @tparam That $thatinfo | ||||
* @param bf $bfinfo | ||||
* @return a new collection of type `That` resulting from applying | ||||
* the given collection-valued function `f` to each element | ||||
* of the outer $coll that satisfies predicate `p` and | ||||
* concatenating the results. | ||||
* | ||||
* @usecase def flatMap[B](f: A => TraversableOnce[B]): $Coll[B] | ||||
* | ||||
* @return a new $coll resulting from applying the given collection-valued function | ||||
* `f` to each element of the outer $coll that satisfies predicate `p` and concatenating the results. | ||||
*/ | ||||
def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = { | ||||
val b = bf(repr) | ||||
for (x <- self) | ||||
if (p(x)) b ++= f(x).seq | ||||
b.result | ||||
} | ||||
/** Applies a function `f` to all elements of the outer $coll containing | ||||
* this `WithFilter` instance that satisfy predicate `p`. | ||||
* | ||||
* @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 = | ||||
for (x <- self) | ||||
if (p(x)) f(x) | ||||
/** Further refines the filter for this $coll. | ||||
* | ||||
* @param q the predicate used to test elements. | ||||
* @return an object of class `WithFilter`, which supports | ||||
* `map`, `flatMap`, `foreach`, and `withFilter` operations. | ||||
* All these operations apply to those elements of this $coll which | ||||
* satisfy the predicate `q` in addition to the predicate `p`. | ||||
*/ | ||||
def withFilter(q: A => Boolean): WithFilter = | ||||
new WithFilter(x => p(x) && q(x)) | ||||
} | ||||
// A helper for tails and inits. | ||||
private def iterateUntilEmpty(f: Traversable[A @uV] => Traversable[A @uV]): Iterator[Repr] = { | ||||
val it = Iterator.iterate(thisCollection)(f) takeWhile (x => !x.isEmpty) | ||||
it ++ Iterator(Nil) map (newBuilder ++= _ result) | ||||
} | ||||
} | ||||
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