/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.collection
import mutable.{ Buffer, ListBuffer, ArrayBuffer }
import annotation.unchecked.{ uncheckedVariance => uV }
/** A template trait for collections which can be traversed either once only
* or one or more times.
* $traversableonceinfo
*
* @tparam A the element type of the collection
*
* @define traversableonceinfo
* This trait exists primarily to eliminate code duplication between
* `Iterator` and `Traversable`, and thus implements some of the common
* methods that can be implemented solely in terms of foreach without
* access to a `Builder`. It also includes a number of abstract methods
* whose implementations are provided by `Iterator`, `Traversable`, etc.
* It contains implementations common to `Iterators` and
* `Traversables`, such as folds, conversions, and other operations which
* traverse some or all of the elements and return a derived value.
* Directly subclassing `TraversableOnce` is not recommended - instead,
* consider declaring an `Iterator` with a `next` and `hasNext` method,
* creating an `Iterator` with one of the methods on the `Iterator` object,
* or declaring a subclass of `Traversable`.
*
* @author Martin Odersky
* @author Paul Phillips
* @version 2.8
* @since 2.8
*
* @define coll traversable or iterator
* @define orderDependentFold
*
* Note: might return different results for different runs, unless the
* underlying collection type is ordered or the operator is associative
* and commutative.
* @define willNotTerminateInf
*
* Note: will not terminate for infinite-sized collections.
*/
trait TraversableOnce[+A] {
self =>
/** Self-documenting abstract methods. */
def foreach[U](f: A => U): Unit
def isEmpty: Boolean
def hasDefiniteSize: Boolean
/** Tests whether this $coll can be repeatedly traversed. Always
* true for Traversables and false for Iterators unless overridden.
*
* @return `true` if it is repeatedly traversable, `false` otherwise.
*/
def isTraversableAgain: Boolean
/** Returns an Iterator over the elements in this $coll. Will return
* the same Iterator if this instance is already an Iterator.
* $willNotTerminateInf
* @return an Iterator containing all elements of this $coll.
*/
def toIterator: Iterator[A]
/** Converts this $coll to an unspecified Traversable. Will return
* the same collection if this instance is already Traversable.
* $willNotTerminateInf
* @return a Traversable containing all elements of this $coll.
*/
def toTraversable: Traversable[A]
/** Converts this $coll to a stream.
* $willNotTerminateInf
* @return a stream containing all elements of this $coll.
*/
def toStream: Stream[A]
// Note: We could redefine this in TraversableLike to always return `repr`
// of type `Repr`, only if `Repr` had type bounds, which it doesn't, because
// not all `Repr` are a subtype `TraversableOnce[A]`.
// The alternative is redefining it for maps, sets and seqs. For concrete implementations
// we don't have to do this anyway, since they are leaves in the inheritance hierarchy.
/** A version of this collection with all
* of the operations implemented sequentially (i.e. in a single-threaded manner).
*
* This method returns a reference to this collection. In parallel collections,
* it is redefined to return a sequential implementation of this collection. In
* both cases, it has O(1) complexity.
*
* @return a sequential view of the collection.
*/
def seq: TraversableOnce[A] = this
/** Presently these are abstract because the Traversable versions use
* breakable/break, and I wasn't sure enough of how that's supposed to
* function to consolidate them with the Iterator versions.
*/
def forall(p: A => Boolean): Boolean
def exists(p: A => Boolean): Boolean
def find(p: A => Boolean): Option[A]
def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Unit
// for internal use
protected[this] def reversed = {
var elems: List[A] = Nil
self.seq foreach (elems ::= _)
elems
}
/** The size of this $coll.
*
* $willNotTerminateInf
*
* @return the number of elements in this $coll.
*/
def size: Int = {
var result = 0
for (x <- self) result += 1
result
}
/** Tests whether the $coll is not empty.
*
* @return `true` if the $coll contains at least one element, `false` otherwise.
*/
def nonEmpty: Boolean = !isEmpty
/** Counts the number of elements in the $coll which satisfy a predicate.
*
* @param p the predicate used to test elements.
* @return the number of elements satisfying the predicate `p`.
*/
def count(p: A => Boolean): Int = {
var cnt = 0
for (x <- this)
if (p(x)) cnt += 1
cnt
}
/** Finds the first element of the $coll for which the given partial
* function is defined, and applies the partial function to it.
*
* $mayNotTerminateInf
* $orderDependent
*
* @param pf the partial function
* @return an option value containing pf applied to the first
* value for which it is defined, or `None` if none exists.
* @example `Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)`
*/
def collectFirst[B](pf: PartialFunction[A, B]): Option[B] = {
for (x <- self.toIterator) { // make sure to use an iterator or `seq`
if (pf isDefinedAt x)
return Some(pf(x))
}
None
}
/** Applies a binary operator to a start value and all elements of this $coll,
* going left to right.
*
* Note: `/:` is alternate syntax for `foldLeft`; `z /: xs` is the same as
* `xs foldLeft z`.
* $willNotTerminateInf
* $orderDependentFold
*
* @param z the start value.
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return the result of inserting `op` between consecutive elements of this $coll,
* going left to right with the start value `z` on the left:
* {{{
* op(...op(op(z, x,,1,,), x,,2,,), ..., x,,n,,)
* }}}
* where `x,,1,,, ..., x,,n,,` are the elements of this $coll.
*/
def /:[B](z: B)(op: (B, A) => B): B = foldLeft(z)(op)
/** Applies a binary operator to all elements of this $coll and a start value,
* going right to left.
*
* Note: `:\` is alternate syntax for `foldRight`; `xs :\ z` is the same as
* `xs foldRight z`.
* $willNotTerminateInf
* $orderDependentFold
*
* @param z the start value
* @param op the binary operator
* @tparam B the result type of the binary operator.
* @return the result of inserting `op` between consecutive elements of this $coll,
* going right to left with the start value `z` on the right:
* {{{
* op(x,,1,,, op(x,,2,,, ... op(x,,n,,, z)...))
* }}}
* where `x,,1,,, ..., x,,n,,` are the elements of this $coll.
*/
def :\[B](z: B)(op: (A, B) => B): B = foldRight(z)(op)
/** Applies a binary operator to a start value and all elements of this $coll,
* going left to right.
*
* $willNotTerminateInf
* $orderDependentFold
*
* @param z the start value.
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return the result of inserting `op` between consecutive elements of this $coll,
* going left to right with the start value `z` on the left:
* {{{
* op(...op(z, x,,1,,), x,,2,,, ..., x,,n,,)
* }}}
* where `x,,1,,, ..., x,,n,,` are the elements of this $coll.
*/
def foldLeft[B](z: B)(op: (B, A) => B): B = {
var result = z
this.seq foreach (x => result = op(result, x))
result
}
/** Applies a binary operator to all elements of this $coll and a start value,
* going right to left.
*
* $willNotTerminateInf
* $orderDependentFold
* @param z the start value.
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return the result of inserting `op` between consecutive elements of this $coll,
* going right to left with the start value `z` on the right:
* {{{
* op(x,,1,,, op(x,,2,,, ... op(x,,n,,, z)...))
* }}}
* where `x,,1,,, ..., x,,n,,` are the elements of this $coll.
*/
def foldRight[B](z: B)(op: (A, B) => B): B =
reversed.foldLeft(z)((x, y) => op(y, x))
/** Applies a binary operator to all elements of this $coll, going left to right.
* $willNotTerminateInf
* $orderDependentFold
*
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return the result of inserting `op` between consecutive elements of this $coll,
* going left to right:
* {{{
* op(...(op(x,,1,,, x,,2,,), ... ) , x,,n,,)
* }}}
* where `x,,1,,, ..., x,,n,,` are the elements of this $coll.
* @throws `UnsupportedOperationException` if this $coll is empty.
*/
def reduceLeft[B >: A](op: (B, A) => B): B = {
if (isEmpty)
throw new UnsupportedOperationException("empty.reduceLeft")
var first = true
var acc: B = 0.asInstanceOf[B]
for (x <- self) {
if (first) {
acc = x
first = false
}
else acc = op(acc, x)
}
acc
}
/** Applies a binary operator to all elements of this $coll, going right to left.
* $willNotTerminateInf
* $orderDependentFold
*
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return the result of inserting `op` between consecutive elements of this $coll,
* going right to left:
* {{{
* op(x,,1,,, op(x,,2,,, ..., op(x,,n-1,,, x,,n,,)...))
* }}}
* where `x,,1,,, ..., x,,n,,` are the elements of this $coll.
* @throws `UnsupportedOperationException` if this $coll is empty.
*/
def reduceRight[B >: A](op: (A, B) => B): B = {
if (isEmpty)
throw new UnsupportedOperationException("empty.reduceRight")
reversed.reduceLeft[B]((x, y) => op(y, x))
}
/** Optionally applies a binary operator to all elements of this $coll, going left to right.
* $willNotTerminateInf
* $orderDependentFold
*
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return an option value containing the result of `reduceLeft(op)` is this $coll is nonempty,
* `None` otherwise.
*/
def reduceLeftOption[B >: A](op: (B, A) => B): Option[B] =
if (isEmpty) None else Some(reduceLeft(op))
/** Optionally applies a binary operator to all elements of this $coll, going
* right to left.
* $willNotTerminateInf
* $orderDependentFold
*
* @param op the binary operator.
* @tparam B the result type of the binary operator.
* @return an option value containing the result of `reduceRight(op)` is this $coll is nonempty,
* `None` otherwise.
*/
def reduceRightOption[B >: A](op: (A, B) => B): Option[B] =
if (isEmpty) None else Some(reduceRight(op))
/** Sums up the elements of this collection.
*
* @param num an implicit parameter defining a set of numeric operations
* which includes the `+` operator to be used in forming the sum.
* @tparam B the result type of the `+` operator.
* @return the sum of all elements of this $coll with respect to the `+` operator in `num`.
*
* @usecase def sum: A
*
* @return the sum of all elements in this $coll of numbers of type `Int`.
* Instead of `Int`, any other type `T` with an implicit `Numeric[T]` implementation
* can be used as element type of the $coll and as result type of `sum`.
* Examples of such types are: `Long`, `Float`, `Double`, `BigInt`.
*
*/
def sum[B >: A](implicit num: Numeric[B]): B = foldLeft(num.zero)(num.plus)
/** Multiplies up the elements of this collection.
*
* @param num an implicit parameter defining a set of numeric operations
* which includes the `*` operator to be used in forming the product.
* @tparam B the result type of the `*` operator.
* @return the product of all elements of this $coll with respect to the `*` operator in `num`.
*
* @usecase def product: A
*
* @return the product of all elements in this $coll of numbers of type `Int`.
* Instead of `Int`, any other type `T` with an implicit `Numeric[T]` implementation
* can be used as element type of the $coll and as result type of `product`.
* Examples of such types are: `Long`, `Float`, `Double`, `BigInt`.
*/
def product[B >: A](implicit num: Numeric[B]): B = foldLeft(num.one)(num.times)
/** Finds the smallest element.
*
* @param cmp An ordering to be used for comparing elements.
* @tparam B The type over which the ordering is defined.
* @return the smallest element of this $coll with respect to the ordering `cmp`.
*
* @usecase def min: A
* @return the smallest element of this $coll
*/
def min[B >: A](implicit cmp: Ordering[B]): A = {
if (isEmpty)
throw new UnsupportedOperationException("empty.min")
reduceLeft((x, y) => if (cmp.lteq(x, y)) x else y)
}
/** Finds the largest element.
*
* @param cmp An ordering to be used for comparing elements.
* @tparam B The type over which the ordering is defined.
* @return the largest element of this $coll with respect to the ordering `cmp`.
*
* @usecase def max: A
* @return the largest element of this $coll.
*/
def max[B >: A](implicit cmp: Ordering[B]): A = {
if (isEmpty)
throw new UnsupportedOperationException("empty.max")
reduceLeft((x, y) => if (cmp.gteq(x, y)) x else y)
}
def maxBy[B](f: A => B)(implicit cmp: Ordering[B]): A = {
if (isEmpty)
throw new UnsupportedOperationException("empty.maxBy")
reduceLeft((x, y) => if (cmp.gteq(f(x), f(y))) x else y)
}
def minBy[B](f: A => B)(implicit cmp: Ordering[B]): A = {
if (isEmpty)
throw new UnsupportedOperationException("empty.minBy")
reduceLeft((x, y) => if (cmp.lteq(f(x), f(y))) x else y)
}
/** Copies all elements of this $coll to a buffer.
* $willNotTerminateInf
* @param dest The buffer to which elements are copied.
*/
def copyToBuffer[B >: A](dest: Buffer[B]): Unit = dest ++= self
/** Copies values of this $coll to an array.
* Fills the given array `xs` with values of this $coll, after skipping `start` values.
* Copying will stop once either the end of the current $coll is reached,
* or the end of the array is reached.
*
* $willNotTerminateInf
*
* @param xs the array to fill.
* @param start the starting index.
* @tparam B the type of the elements of the array.
*
* @usecase def copyToArray(xs: Array[A], start: Int): Unit
*/
def copyToArray[B >: A](xs: Array[B], start: Int): Unit =
copyToArray(xs, start, xs.length - start)
/** Copies values of this $coll to an array.
* Fills the given array `xs` with values of this $coll.
* Copying will stop once either the end of the current $coll is reached,
* or the end of the array is reached.
*
* $willNotTerminateInf
*
* @param xs the array to fill.
* @tparam B the type of the elements of the array.
*
* @usecase def copyToArray(xs: Array[A]): Unit
*/
def copyToArray[B >: A](xs: Array[B]): Unit =
copyToArray(xs, 0, xs.length)
/** Converts this $coll to an array.
* $willNotTerminateInf
*
* @tparam B the type of the elements of the array. A `ClassManifest` for
* this type must be available.
* @return an array containing all elements of this $coll.
*
* @usecase def toArray: Array[A]
* @return an array containing all elements of this $coll.
* A `ClassManifest` must be available for the element type of this $coll.
*/
def toArray[B >: A : ClassManifest]: Array[B] = {
if (isTraversableAgain) {
val result = new Array[B](size)
copyToArray(result, 0)
result
}
else toBuffer.toArray
}
/** Converts this $coll to a list.
* $willNotTerminateInf
* @return a list containing all elements of this $coll.
*/
def toList: List[A] = new ListBuffer[A] ++= self toList
/** Converts this $coll to an iterable collection. Note that
* the choice of target `Iterable` is lazy in this default implementation
* as this `TraversableOnce` may be lazy and unevaluated (i.e. it may
* be an iterator which is only traversable once).
*
* $willNotTerminateInf
* @return an `Iterable` containing all elements of this $coll.
*/
def toIterable: Iterable[A] = toStream
/** Converts this $coll to a sequence. As with `toIterable`, it's lazy
* in this default implementation, as this `TraversableOnce` may be
* lazy and unevaluated.
*
* $willNotTerminateInf
* @return a sequence containing all elements of this $coll.
*/
def toSeq: Seq[A] = toStream
/** Converts this $coll to an indexed sequence.
* $willNotTerminateInf
* @return an indexed sequence containing all elements of this $coll.
*/
def toIndexedSeq[B >: A]: immutable.IndexedSeq[B] = immutable.IndexedSeq() ++ self
/** Converts this $coll to a mutable buffer.
* $willNotTerminateInf
* @return a buffer containing all elements of this $coll.
*/
def toBuffer[B >: A]: mutable.Buffer[B] = new ArrayBuffer[B] ++= self
/** Converts this $coll to a set.
* $willNotTerminateInf
* @return a set containing all elements of this $coll.
*/
def toSet[B >: A]: immutable.Set[B] = immutable.Set() ++ self
/** Converts this $coll to a map. This method is unavailable unless
* the elements are members of Tuple2, each ((T, U)) becoming a key-value
* pair in the map. Duplicate keys will be overwritten by later keys:
* if this is an unordered collection, which key is in the resulting map
* is undefined.
* $willNotTerminateInf
* @return a map containing all elements of this $coll.
* @usecase def toMap[T, U]: Map[T, U]
* @return a map of type `immutable.Map[T, U]`
* containing all key/value pairs of type `(T, U)` of this $coll.
*/
def toMap[T, U](implicit ev: A <:< (T, U)): immutable.Map[T, U] = {
val b = immutable.Map.newBuilder[T, U]
for (x <- self)
b += x
b.result
}
/** Displays all elements of this $coll in a string using start, end, and
* separator strings.
*
* @param start the starting string.
* @param sep the separator string.
* @param end the ending string.
* @return a string representation of this $coll. The resulting string
* begins with the string `start` and ends with the string
* `end`. Inside, the string representations (w.r.t. the method
* `toString`) of all elements of this $coll are separated by
* the string `sep`.
*
* @example `List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"`
*/
def mkString(start: String, sep: String, end: String): String =
addString(new StringBuilder(), start, sep, end).toString
/** Displays all elements of this $coll in a string using a separator string.
*
* @param sep the separator string.
* @return a string representation of this $coll. In the resulting string
* the string representations (w.r.t. the method `toString`)
* of all elements of this $coll are separated by the string `sep`.
*
* @example `List(1, 2, 3).mkString("|") = "1|2|3"`
*/
def mkString(sep: String): String = mkString("", sep, "")
/** Displays all elements of this $coll in a string.
*
* @return a string representation of this $coll. In the resulting string
* the string representations (w.r.t. the method `toString`)
* of all elements of this $coll follow each other without any
* separator string.
*/
def mkString: String = mkString("")
/** Appends all elements of this $coll to a string builder using start, end,
* and separator strings.
* The written text begins with the string `start` and ends with the string
* `end`. Inside, the string representations (w.r.t. the method `toString`)
* of all elements of this $coll are separated by the string `sep`.
*
* @param b the string builder to which elements are appended.
* @param start the starting string.
* @param sep the separator string.
* @param end the ending string.
* @return the string builder `b` to which elements were appended.
*/
def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder = {
var first = true
b append start
for (x <- self) {
if (first) {
b append x
first = false
}
else {
b append sep
b append x
}
}
b append end
b
}
/** Appends all elements of this $coll to a string builder using a separator
* string. The written text consists of the string representations (w.r.t.
* the method `toString`) of all elements of this $coll, separated by the
* string `sep`.
*
* @param b the string builder to which elements are appended.
* @param sep the separator string.
* @return the string builder `b` to which elements were appended.
*/
def addString(b: StringBuilder, sep: String): StringBuilder = addString(b, "", sep, "")
/** Appends all elements of this $coll to a string builder.
* The written text consists of the string representations (w.r.t. the method
* `toString`) of all elements of this $coll without any separator string.
*
* @param b the string builder to which elements are appended.
* @return the string builder `b` to which elements were appended.
*/
def addString(b: StringBuilder): StringBuilder = addString(b, "")
}
object TraversableOnce {
implicit def traversableOnceCanBuildFrom[T] = new OnceCanBuildFrom[T]
implicit def wrapTraversableOnce[A](trav: TraversableOnce[A]) = new MonadOps(trav)
implicit def flattenTraversableOnce[A, CC[_]](travs: TraversableOnce[CC[A]])(implicit ev: CC[A] => TraversableOnce[A]) =
new FlattenOps[A](travs map ev)
/** With the advent of TraversableOnce, it can be useful to have a builder which
* operates on Iterators so they can be treated uniformly along with the collections.
* See scala.util.Random.shuffle for an example.
*/
class OnceCanBuildFrom[A] extends generic.CanBuildFrom[TraversableOnce[A], A, TraversableOnce[A]] {
def newIterator = new ArrayBuffer[A] mapResult (_.iterator)
/** Creates a new builder on request of a collection.
* @param from the collection requesting the builder to be created.
* @return the result of invoking the `genericBuilder` method on `from`.
*/
def apply(from: TraversableOnce[A]) = newIterator
/** Creates a new builder from scratch
* @return the result of invoking the `newBuilder` method of this factory.
*/
def apply() = newIterator
}
class FlattenOps[A](travs: TraversableOnce[TraversableOnce[A]]) {
def flatten: Iterator[A] = travs.foldLeft(Iterator.empty: Iterator[A])(_ ++ _)
}
class MonadOps[+A](trav: TraversableOnce[A]) {
def map[B](f: A => B): TraversableOnce[B] = trav.toIterator map f
def flatMap[B](f: A => TraversableOnce[B]): TraversableOnce[B] = trav.toIterator flatMap f
def withFilter(p: A => Boolean) = trav.toIterator filter p
def filter(p: A => Boolean): TraversableOnce[A] = withFilter(p)
}
}
