scala.collection.TraversableViewLike

trait TraversableViewLike[+A, +Coll, +This <: TraversableView[A, Coll] with TraversableViewLike[A, Coll, This]] extends Traversable[A] with TraversableLike[A, This] with ViewMkString[A]

A template trait for non-strict views of traversable collections.

A view is a lazy version of some collection. Collection transformers such as map or filter or ++ do not traverse any elements when applied on a view. Instead they create a new view which simply records that fact that the operation needs to be applied. The collection elements are accessed, and the view operations are applied, when a non-view result is needed, or when the force method is called on a view.

All views for traversable collections are defined by creating a new foreach method.

Implementation note: Methods such as map or flatMap on this view will not invoke the implicitly passed Builder factory, but will return a new view directly, to preserve by-name behavior. The new view is then cast to the factory’s result type. This means that every CanBuildFrom that takes a View as its From type parameter must yield the same view (or a generic superclass of it) as its result parameter. If that assumption is broken, cast errors might result.

• Self Type
  • TraversableViewLike [A, Coll, This]
• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

Type Members

trait Appended[B >: A] extends Transformed[B]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait DroppedWhile extends Transformed[A]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait EmptyView extends Transformed[Nothing]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait Filtered extends Transformed[A]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait FlatMapped[B] extends Transformed[B]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait Forced[B] extends Transformed[B]

A fall back which forces everything into a vector and then applies an operation on it. Used for those operations which do not naturally lend themselves to a view

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait Mapped[B] extends Transformed[B]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait Prepended[B >: A] extends Transformed[B]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

type Self = This

The type implementing this traversable

• Attributes
  • protected[this]
• Definition Classes
  • TraversableLike

trait Sliced extends Transformed[A]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait TakenWhile extends Transformed[A]

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

trait Transformed[+B] extends TraversableView[B, Coll]

The implementation base trait of this view. This trait and all its subtraits has to be re-implemented for each ViewLike class.

• Source
  • TraversableViewLike.scala - Blame
  • TraversableViewLike.scala - History

class WithFilter extends FilterMonadic[A, Repr]

A class supporting filtered operations. Instances of this class are returned by method withFilter .

• Definition Classes
  • TraversableLike

Concrete Value Members From scala.collection.Parallelizable

def par: ParIterable[A]

Returns a parallel implementation of this collection.

For most collection types, this method creates a new parallel collection by copying all the elements. For these collection, par takes linear time. Mutable collections in this category do not produce a mutable parallel collection that has the same underlying dataset, so changes in one collection will not be reflected in the other one.

Specific collections (e.g. ParArray or mutable.ParHashMap ) override this default behaviour by creating a parallel collection which shares the same underlying dataset. For these collections, par takes constant or sublinear time.

All parallel collections return a reference to themselves.

• returns
  • a parallel implementation of this collection
• Definition Classes
  • Parallelizable

(defined at scala.collection.Parallelizable)

Concrete Value Members From scala.collection.Traversable

def companion: GenericCompanion[Traversable]

The factory companion object that builds instances of class Traversable. (or its Iterable superclass where class Traversable is not a Seq .)

• Definition Classes
  • Traversable → GenTraversable → GenericTraversableTemplate

(defined at scala.collection.Traversable)

Concrete Value Members From scala.collection.TraversableLike

def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Unit

[use case]

Copies the elements of this collection to an array. Fills the given array xs with at most len elements of this collection, starting at position start . Copying will stop once either the end of the current collection is reached, or the end of the target array is reached, or len elements have been copied.

Note: will not terminate for infinite-sized collections.

• xs
  • the array to fill.
• start
  • the starting index.
• len
  • the maximal number of elements to copy.
• Definition Classes
  • TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableLike)

def exists(p: (A) ⇒ Boolean): Boolean

Tests whether a predicate holds for at least one element of this traversable collection.

Note: may not terminate for infinite-sized collections.

• p
  • the predicate used to test elements.
• returns
  • false if this traversable collection is empty, otherwise true if the given predicate p holds for some of the elements of this traversable collection, otherwise false
• Definition Classes
  • TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableLike)

def find(p: (A) ⇒ Boolean): Option[A]

Finds the first element of the traversable collection satisfying a predicate, if any.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• p
  • the predicate used to test elements.
• returns
  • an option value containing the first element in the traversable collection that satisfies p , or None if none exists.
• Definition Classes
  • TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableLike)

def forall(p: (A) ⇒ Boolean): Boolean

Tests whether a predicate holds for all elements of this traversable collection.

Note: may not terminate for infinite-sized collections.

• p
  • the predicate used to test elements.
• returns
  • true if this traversable collection is empty or the given predicate p holds for all elements of this traversable collection, otherwise false .
• Definition Classes
  • TraversableLike → TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableLike)

def parCombiner: Combiner[A, ParIterable[A]]

The default par implementation uses the combiner provided by this method to create a new parallel collection.

• returns
  • a combiner for the parallel collection of type ParRepr
• Attributes
  • protected[this]
• Definition Classes
  • TraversableLike → Parallelizable

(defined at scala.collection.TraversableLike)

def repr: This

The collection of type traversable collection underlying this TraversableLike object. By default this is implemented as the TraversableLike object itself, but this can be overridden.

• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def scan[B >: A, That](z: B)(op: (B, B) ⇒ B)(implicit cbf: CanBuildFrom[This, B, That]): That

Computes a prefix scan of the elements of the collection.

Note: The neutral element z may be applied more than once.

• B
  • element type of the resulting collection
• That
  • type of the resulting collection
• z
  • neutral element for the operator op
• op
  • the associative operator for the scan
• cbf
  • combiner factory which provides a combiner
• returns
  • a new traversable collection containing the prefix scan of the elements in this traversable collection
• Definition Classes
  • TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableLike)

def toCollection(repr: This): Traversable[A]

A conversion from collections of type Repr to Traversable objects. By default this is implemented as just a cast, but this can be overridden.

• Attributes
  • protected[this]
• Definition Classes
  • TraversableLike

(defined at scala.collection.TraversableLike)

def view(from: Int, until: Int): TraversableView[A, This]

Creates a non-strict view of a slice of this traversable collection.

Note: the difference between view and slice is that view produces a view of the current traversable collection, whereas slice produces a new traversable collection.

Note: view(from, to) is equivalent to view.slice(from, to)

Note: might return different results for different runs, unless the underlying collection type is ordered.

• from
  • the index of the first element of the view
• until
  • the index of the element following the view
• returns
  • a non-strict view of a slice of this traversable collection, starting at index from and extending up to (but not including) index until .
• Definition Classes
  • TraversableLike

(defined at scala.collection.TraversableLike)

def view: TraversableView[A, This]

Creates a non-strict view of this traversable collection.

• returns
  • a non-strict view of this traversable collection.
• Definition Classes
  • TraversableLike

(defined at scala.collection.TraversableLike)

Concrete Value Members From scala.collection.TraversableOnce

def /:[B](z: B)(op: (B, A) ⇒ B): B

Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.

Note: /: is alternate syntax for foldLeft ; z /: xs is the same as xs foldLeft z .

Examples:

Note that the folding function used to compute b is equivalent to that used to compute c.

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = (5 /: a)(_+_)
b: Int = 15

scala> val c = (5 /: a)((x,y) => x + y)
c: Int = 15

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• z
  • the start value.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going left to right with the start value z on the left:

    op(...op(op(z, x_1), x_2), ..., x_n)
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def :\[B](z: B)(op: (A, B) ⇒ B): B

Applies a binary operator to all elements of this traversable or iterator and a start value, going right to left.

Note: :\ is alternate syntax for foldRight ; xs :\ z is the same as xs foldRight z .

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

Examples:

Note that the folding function used to compute b is equivalent to that used to compute c.

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = (a :\ 5)(_+_)
b: Int = 15

scala> val c = (a :\ 5)((x,y) => x + y)
c: Int = 15

• B
  • the result type of the binary operator.
• z
  • the start value
• op
  • the binary operator
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going right to left with the start value z on the right:

    op(x_1, op(x_2, ... op(x_n, z)...))
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def addString(b: StringBuilder): StringBuilder

Appends all elements of this traversable or iterator to a string builder. The written text consists of the string representations (w.r.t. the method toString ) of all elements of this traversable or iterator without any separator string.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> val h = a.addString(b)
h: StringBuilder = 1234

• b
  • the string builder to which elements are appended.
• returns
  • the string builder b to which elements were appended.
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def addString(b: StringBuilder, sep: String): StringBuilder

Appends all elements of this traversable or iterator 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 traversable or iterator, separated by the string sep .

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> a.addString(b, ", ")
res0: StringBuilder = 1, 2, 3, 4

• b
  • the string builder to which elements are appended.
• sep
  • the separator string.
• returns
  • the string builder b to which elements were appended.
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def aggregate[B](z: ⇒ B)(seqop: (B, A) ⇒ B, combop: (B, B) ⇒ B): B

Aggregates the results of applying an operator to subsequent elements.

This is a more general form of fold and reduce . It is similar to foldLeft in that it doesn’t require the result to be a supertype of the element type. In addition, it allows parallel collections to be processed in chunks, and then combines the intermediate results.

aggregate splits the traversable or iterator into partitions and processes each partition by sequentially applying seqop , starting with z (like foldLeft ). Those intermediate results are then combined by using combop (like fold ). The implementation of this operation may operate on an arbitrary number of collection partitions (even 1), so combop may be invoked an arbitrary number of times (even 0).

As an example, consider summing up the integer values of a list of chars. The initial value for the sum is 0. First, seqop transforms each input character to an Int and adds it to the sum (of the partition). Then, combop just needs to sum up the intermediate results of the partitions:

List('a', 'b', 'c').aggregate(0)({ (sum, ch) => sum + ch.toInt }, { (p1, p2) => p1 + p2 })

• B
  • the type of accumulated results
• z
  • the initial value for the accumulated result of the partition - this will typically be the neutral element for the seqop operator (e.g. Nil for list concatenation or 0 for summation) and may be evaluated more than once
• seqop
  • an operator used to accumulate results within a partition
• combop
  • an associative operator used to combine results from different partitions
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def collectFirst[B](pf: PartialFunction[A, B]): Option[B]

Finds the first element of the traversable or iterator for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• pf
  • the partial function
• returns
  • an option value containing pf applied to the first value for which it is defined, or None if none exists.
• Definition Classes
  • TraversableOnce

Example:

Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)

(defined at scala.collection.TraversableOnce)

def copyToArray[B >: A](xs: Array[B]): Unit

[use case]

Copies the elements of this collection to an array. Fills the given array xs with values of this collection. Copying will stop once either the end of the current collection is reached, or the end of the target array is reached.

Note: will not terminate for infinite-sized collections.

• xs
  • the array to fill.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def copyToArray[B >: A](xs: Array[B], start: Int): Unit

[use case]

Copies the elements of this collection to an array. Fills the given array xs with values of this collection, beginning at index start . Copying will stop once either the end of the current collection is reached, or the end of the target array is reached.

Note: will not terminate for infinite-sized collections.

• xs
  • the array to fill.
• start
  • the starting index.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def copyToBuffer[B >: A](dest: Buffer[B]): Unit

Copies all elements of this traversable or iterator to a buffer.

Note: will not terminate for infinite-sized collections.

• dest
  • The buffer to which elements are copied.
• Definition Classes
  • TraversableOnce

(defined at scala.collection.TraversableOnce)

def count(p: (A) ⇒ Boolean): Int

Counts the number of elements in the traversable or iterator which satisfy a predicate.

• p
  • the predicate used to test elements.
• returns
  • the number of elements satisfying the predicate p .
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def foldLeft[B](z: B)(op: (B, A) ⇒ B): B

Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• z
  • the start value.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going left to right with the start value z on the left:

    op(...op(z, x_1), x_2, ..., x_n)
    

where `x1, ..., xn` are the elements of this traversable or iterator.
Returns `z` if this traversable or iterator is empty.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def foldRight[B](z: B)(op: (A, B) ⇒ B): B

Applies a binary operator to all elements of this traversable or iterator and a start value, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• z
  • the start value.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going right to left with the start value z on the right:

    op(x_1, op(x_2, ... op(x_n, z)...))
    

where `x1, ..., xn` are the elements of this traversable or iterator.
Returns `z` if this traversable or iterator is empty.

• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def fold[A1 >: A](z: A1)(op: (A1, A1) ⇒ A1): A1

Folds the elements of this traversable or iterator using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

Note: will not terminate for infinite-sized collections.

• A1
  • a type parameter for the binary operator, a supertype of A .
• z
  • a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for list concatenation, 0 for addition, or 1 for multiplication).
• op
  • a binary operator that must be associative.
• returns
  • the result of applying the fold operator op between all the elements and z , or z if this traversable or iterator is empty.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def maxBy[B](f: (A) ⇒ B)(implicit cmp: Ordering[B]): A

[use case]

Finds the first element which yields the largest value measured by function f.

• B
  • The result type of the function f.
• f
  • The measuring function.
• returns
  • the first element of this collection with the largest value measured by function f.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def minBy[B](f: (A) ⇒ B)(implicit cmp: Ordering[B]): A

[use case]

Finds the first element which yields the smallest value measured by function f.

• B
  • The result type of the function f.
• f
  • The measuring function.
• returns
  • the first element of this collection with the smallest value measured by function f.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduceLeftOption[B >: A](op: (B, A) ⇒ B): Option[B]

Optionally applies a binary operator to all elements of this traversable or iterator, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • an option value containing the result of reduceLeft(op) if this traversable or iterator is nonempty, None otherwise.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduceLeft[B >: A](op: (B, A) ⇒ B): B

Applies a binary operator to all elements of this traversable or iterator, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going left to right:

    op( op( ... op(x_1, x_2) ..., x_{n-1}), x_n)
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce
• Exceptions thrown
  • UnsupportedOperationException if this traversable or iterator is empty.

(defined at scala.collection.TraversableOnce)

def reduceOption[A1 >: A](op: (A1, A1) ⇒ A1): Option[A1]

Reduces the elements of this traversable or iterator, if any, using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

• A1
  • A type parameter for the binary operator, a supertype of A .
• op
  • A binary operator that must be associative.
• returns
  • An option value containing result of applying reduce operator op between all the elements if the collection is nonempty, and None otherwise.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduceRightOption[B >: A](op: (A, B) ⇒ B): Option[B]

Optionally applies a binary operator to all elements of this traversable or iterator, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • an option value containing the result of reduceRight(op) if this traversable or iterator is nonempty, None otherwise.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def reduceRight[B >: A](op: (A, B) ⇒ B): B

Applies a binary operator to all elements of this traversable or iterator, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

• B
  • the result type of the binary operator.
• op
  • the binary operator.
• returns
  • the result of inserting op between consecutive elements of this traversable or iterator, going right to left:

    op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
    

where `x1, ..., xn` are the elements of this traversable or iterator.

• Definition Classes
  • TraversableOnce → GenTraversableOnce
• Exceptions thrown
  • UnsupportedOperationException if this traversable or iterator is empty.

(defined at scala.collection.TraversableOnce)

def reduce[A1 >: A](op: (A1, A1) ⇒ A1): A1

Reduces the elements of this traversable or iterator using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

• A1
  • A type parameter for the binary operator, a supertype of A .
• op
  • A binary operator that must be associative.
• returns
  • The result of applying reduce operator op between all the elements if the traversable or iterator is nonempty.
• Definition Classes
  • TraversableOnce → GenTraversableOnce
• Exceptions thrown
  • UnsupportedOperationException if this traversable or iterator is empty.

(defined at scala.collection.TraversableOnce)

def toBuffer[B >: A]: Buffer[B]

Uses the contents of this traversable or iterator to create a new mutable buffer.

Note: will not terminate for infinite-sized collections.

• returns
  • a buffer containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toIndexedSeq: immutable.IndexedSeq[A]

Converts this traversable or iterator to an indexed sequence.

Note: will not terminate for infinite-sized collections.

• returns
  • an indexed sequence containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toMap[T, U](implicit ev: <:<[A, (T, U)]): immutable.Map[T, U]

[use case]

Converts this collection 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.

Note: will not terminate for infinite-sized collections.

• returns
  • a map of type immutable.Map[T, U] containing all key/value pairs of type (T, U) of this collection.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

def toSet[B >: A]: immutable.Set[B]

Converts this traversable or iterator to a set.

Note: will not terminate for infinite-sized collections.

• returns
  • a set containing all elements of this traversable or iterator.
• Definition Classes
  • TraversableOnce → GenTraversableOnce

(defined at scala.collection.TraversableOnce)

Concrete Value Members From scala.collection.TraversableViewLike

abstract def underlying: Coll

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def ++:[B >: A, That](xs: Traversable[B])(implicit bf: CanBuildFrom[This, B, That]): That

As with ++ , returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = LinkedList(2)
y: scala.collection.mutable.LinkedList[Int] = LinkedList(2)

scala> val z = x ++: y
z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)

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.

• B
  • the element type of the returned collection.
• That
  • the class of the returned collection. Where possible, That is the same class as the current collection class Repr , but this depends on the element type B being admissible for that class, which means that an implicit instance of type CanBuildFrom[Repr, B, That] is found.
• bf
  • an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and and the new element type B .
• returns
  • a new collection of type That which contains all elements of this collection followed by all elements of that .
• Definition Classes
  • TraversableViewLike → TraversableLike

(defined at scala.collection.TraversableViewLike)

def ++:[B >: A, That](xs: TraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

As with ++ , returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from ++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = LinkedList(2)
y: scala.collection.mutable.LinkedList[Int] = LinkedList(2)

scala> val z = x ++: y
z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)

• B
  • the element type of the returned collection.
• that
  • the traversable to append.
• returns
  • a new collection which contains all elements of this collection followed by all elements of that .
• Definition Classes
  • TraversableViewLike → TraversableLike

(defined at scala.collection.TraversableViewLike)

def ++[B >: A, That](xs: GenTraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Returns a new collection containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the collection is the most specific superclass encompassing the element types of the two operands.

Example:

scala> val a = List(1)
a: List[Int] = List(1)

scala> val b = List(2)
b: List[Int] = List(2)

scala> val c = a ++ b
c: List[Int] = List(1, 2)

scala> val d = List('a')
d: List[Char] = List(a)

scala> val e = c ++ d
e: List[AnyVal] = List(1, 2, a)

• B
  • the element type of the returned collection.
• that
  • the traversable to append.
• returns
  • a new collection which contains all elements of this collection followed by all elements of that .
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Builds a new collection by applying a partial function to all elements of this collection on which the function is defined.

• B
  • the element type of the returned collection.
• pf
  • the partial function which filters and maps the collection.
• returns
  • a new collection resulting from applying the given partial function pf to each element on which it is defined and collecting the results. The order of the elements is preserved.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def drop(n: Int): This

Selects all elements except first n ones.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the number of elements to drop from this collection.
• returns
  • a collection consisting of all elements of this collection except the first n ones, or else the empty collection, if this collection has less than n elements.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def dropWhile(p: (A) ⇒ Boolean): This

Drops longest prefix of elements that satisfy a predicate.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the longest suffix of this collection whose first element does not satisfy the predicate p .
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def filter(p: (A) ⇒ Boolean): This

Selects all elements of this collection which satisfy a predicate.

• p
  • the predicate used to test elements.
• returns
  • a new collection consisting of all elements of this collection that satisfy the given predicate p . The order of the elements is preserved.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def filterNot(p: (A) ⇒ Boolean): This

Selects all elements of this collection which do not satisfy a predicate.

• p
  • the predicate used to test elements.
• returns
  • a new collection consisting of all elements of this collection that do not satisfy the given predicate p . The order of the elements is preserved.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def flatMap[B, That](f: (A) ⇒ GenTraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Builds a new collection by applying a function to all elements of this collection and using the elements of the resulting collections.

For example:

def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")

The type of the resulting collection is guided by the static type of collection. This might cause unexpected results sometimes. For example:

// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)

// lettersOf will return a Set[Char], not a Seq
def lettersOf(words: Seq[String]) = words.toSet flatMap (word => word.toSeq)

// xs will be an Iterable[Int]
val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)

// ys will be a Map[Int, Int]
val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)

• B
  • the element type of the returned collection.
• f
  • the function to apply to each element.
• returns
  • a new collection resulting from applying the given collection-valued function f to each element of this collection and concatenating the results.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike → FilterMonadic

(defined at scala.collection.TraversableViewLike)

def force[B >: A, That](implicit bf: CanBuildFrom[Coll, B, That]): That

(defined at scala.collection.TraversableViewLike)

def groupBy[K](f: (A) ⇒ K): immutable.Map[K, This]

Partitions this collection into a map of collections according to some discriminator function.

Note: this method is not re-implemented by views. This means when applied to a view it will always force the view and return a new collection.

• K
  • the type of keys returned by the discriminator function.
• f
  • the discriminator function.
• returns
  • A map from keys to collections such that the following invariant holds:

    (xs groupBy f)(k) = xs filter (x => f(x) == k)
    

That is, every key `k` is bound to a collection of those elements `x` for
which `f(x)` equals `k` .

• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def map[B, That](f: (A) ⇒ B)(implicit bf: CanBuildFrom[This, B, That]): That

[use case]

Builds a new collection by applying a function to all elements of this collection.

• B
  • the element type of the returned collection.
• f
  • the function to apply to each element.
• returns
  • a new collection resulting from applying the given function f to each element of this collection and collecting the results.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike → FilterMonadic

(defined at scala.collection.TraversableViewLike)

def newAppended[B >: A](that: GenTraversable[B]): Transformed[B]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newBuilder: Builder[A, This]

The builder that builds instances of type Traversable[A]

• Attributes
  • protected[this]
• Definition Classes
  • TraversableViewLike → GenericTraversableTemplate → TraversableLike → HasNewBuilder

(defined at scala.collection.TraversableViewLike)

def newDropped(n: Int): Transformed[A]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newDroppedWhile(p: (A) ⇒ Boolean): Transformed[A]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newFiltered(p: (A) ⇒ Boolean): Transformed[A]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newFlatMapped[B](f: (A) ⇒ GenTraversableOnce[B]): Transformed[B]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newForced[B](xs: ⇒ GenSeq[B]): Transformed[B]

Boilerplate method, to override in each subclass This method could be eliminated if Scala had virtual classes

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newMapped[B](f: (A) ⇒ B): Transformed[B]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newPrepended[B >: A](that: GenTraversable[B]): Transformed[B]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newSliced(_endpoints: SliceInterval): Transformed[A]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newTaken(n: Int): Transformed[A]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def newTakenWhile(p: (A) ⇒ Boolean): Transformed[A]

• Attributes
  • protected

(defined at scala.collection.TraversableViewLike)

def partition(p: (A) ⇒ Boolean): (This, This)

Partitions this collection in two collections according to a predicate.

• p
  • the predicate on which to partition.
• returns
  • a pair of collections: the first collection consists of all elements that satisfy the predicate p and the second collection consists of all elements that don’t. The relative order of the elements in the resulting collections is the same as in the original collection.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def scanLeft[B, That](z: B)(op: (B, A) ⇒ B)(implicit bf: CanBuildFrom[This, B, That]): That

Produces a collection containing cumulative results of applying the operator going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• B
  • the type of the elements in the resulting collection
• That
  • the actual type of the resulting collection
• z
  • the initial value
• op
  • the binary operator applied to the intermediate result and the element
• bf
  • an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and and the new element type B .
• returns
  • collection with intermediate results
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def scanRight[B, That](z: B)(op: (A, B) ⇒ B)(implicit bf: CanBuildFrom[This, B, That]): That

Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

Example:

List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)

• B
  • the type of the elements in the resulting collection
• That
  • the actual type of the resulting collection
• z
  • the initial value
• op
  • the binary operator applied to the intermediate result and the element
• bf
  • an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and and the new element type B .
• returns
  • collection with intermediate results
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike
• Annotations
  • @migration
• Migration
  • (Changed in version 2.9.0) The behavior of scanRight has changed. The previous behavior can be reproduced with scanRight.reverse.

(defined at scala.collection.TraversableViewLike)

def slice(from: Int, until: Int): This

Selects an interval of elements. The returned collection is made up of all elements x which satisfy the invariant:

from <= indexOf(x) < until

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • a collection containing the elements greater than or equal to index from extending up to (but not including) index until of this collection.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def span(p: (A) ⇒ Boolean): (This, This)

Splits this collection into a prefix/suffix pair according to a predicate.

Note: c span p is equivalent to (but possibly more efficient than) (c takeWhile p, c dropWhile p) , provided the evaluation of the predicate p does not cause any side-effects.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • a pair consisting of the longest prefix of this collection whose elements all satisfy p , and the rest of this collection.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def splitAt(n: Int): (This, This)

Splits this collection into two at a given position. Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n) .

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the position at which to split.
• returns
  • a pair of collections consisting of the first n elements of this collection, and the other elements.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def take(n: Int): This

Selects first n elements.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• n
  • the number of elements to take from this collection.
• returns
  • a collection consisting only of the first n elements of this collection, or else the whole collection, if it has less than n elements.
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def takeWhile(p: (A) ⇒ Boolean): This

Takes longest prefix of elements that satisfy a predicate.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• returns
  • the longest prefix of this collection whose elements all satisfy the predicate p .
• Definition Classes
  • TraversableViewLike → TraversableLike → GenTraversableLike

(defined at scala.collection.TraversableViewLike)

def unzip3[A1, A2, A3](implicit asTriple: (A) ⇒ (A1, A2, A3)): (Transformed[A1], Transformed[A2], Transformed[A3])

Converts this collection of triples into three collections of the first, second, and third element of each triple.

val xs = Traversable(
           (1, "one", '1'),
           (2, "two", '2'),
           (3, "three", '3')).unzip3
// xs == (Traversable(1, 2, 3),
//        Traversable(one, two, three),
//        Traversable(1, 2, 3))

• A1
  • the type of the first member of the element triples
• A2
  • the type of the second member of the element triples
• A3
  • the type of the third member of the element triples
• asTriple
  • an implicit conversion which asserts that the element type of this collection is a triple.
• returns
  • a triple of collections, containing the first, second, respectively third member of each element triple of this collection.
• Definition Classes
  • TraversableViewLike → GenericTraversableTemplate

(defined at scala.collection.TraversableViewLike)

def unzip[A1, A2](implicit asPair: (A) ⇒ (A1, A2)): (Transformed[A1], Transformed[A2])

Converts this collection of pairs into two collections of the first and second half of each pair.

val xs = Traversable(
           (1, "one"),
           (2, "two"),
           (3, "three")).unzip
// xs == (Traversable(1, 2, 3),
//        Traversable(one, two, three))

• A1
  • the type of the first half of the element pairs
• A2
  • the type of the second half of the element pairs
• asPair
  • an implicit conversion which asserts that the element type of this collection is a pair.
• returns
  • a pair of collections, containing the first, respectively second half of each element pair of this collection.
• Definition Classes
  • TraversableViewLike → GenericTraversableTemplate

(defined at scala.collection.TraversableViewLike)

def withFilter(p: (A) ⇒ Boolean): This

Creates a non-strict filter of this collection.

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.

Note: might return different results for different runs, unless the underlying collection type is ordered.

• p
  • the predicate used to test elements.
• returns
  • an object of class WithFilter , which supports map , flatMap , foreach , and withFilter operations. All these operations apply to those elements of this collection which satisfy the predicate p .
• Definition Classes
  • TraversableViewLike → TraversableLike → FilterMonadic

(defined at scala.collection.TraversableViewLike)

Concrete Value Members From scala.collection.ViewMkString

def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder

• Definition Classes
  • ViewMkString

(defined at scala.collection.ViewMkString)

def mkString(sep: String): String

• Definition Classes
  • ViewMkString

(defined at scala.collection.ViewMkString)

def mkString(start: String, sep: String, end: String): String

• Definition Classes
  • ViewMkString

(defined at scala.collection.ViewMkString)

Concrete Value Members From scala.collection.generic.GenericTraversableTemplate ——————————————————————————–

abstract def foreach[U](f: (A) ⇒ U): Unit

[use case]

• f
  • the function that is applied for its side-effect to every element. The result of function f is discarded.
• Definition Classes
  • GenericTraversableTemplate

(defined at scala.collection.generic.GenericTraversableTemplate)

def genericBuilder[B]: Builder[B, Traversable[B]]

The generic builder that builds instances of Traversable at arbitrary element types.

• Definition Classes
  • GenericTraversableTemplate

(defined at scala.collection.generic.GenericTraversableTemplate)

def transpose[B](implicit asTraversable: (A) ⇒ GenTraversableOnce[B]): Traversable[Traversable[B]]

Transposes this collection of traversable collections into a collection of collections.

The resulting collection’s type will be guided by the static type of collection. For example:

val xs = List(
           Set(1, 2, 3),
           Set(4, 5, 6)).transpose
// xs == List(
//         List(1, 4),
//         List(2, 5),
//         List(3, 6))

val ys = Vector(
           List(1, 2, 3),
           List(4, 5, 6)).transpose
// ys == Vector(
//         Vector(1, 4),
//         Vector(2, 5),
//         Vector(3, 6))

• B
  • the type of the elements of each traversable collection.
• asTraversable
  • an implicit conversion which asserts that the element type of this collection is a Traversable .
• returns
  • a two-dimensional collection of collections which has as n th row the n th column of this collection.
• Definition Classes
  • GenericTraversableTemplate
• Annotations
  • @migration
• Migration
  • (Changed in version 2.9.0) transpose throws an IllegalArgumentException if collections are not uniformly sized.
• Exceptions thrown
  • IllegalArgumentException if all collections in this collection are not of the same size.

(defined at scala.collection.generic.GenericTraversableTemplate)

Concrete Value Members From Implicit scala.collection.parallel.CollectionsHaveToParArray ——————————————————————————–

def toParArray: ParArray[T]

• Implicit information
  • This member is added by an implicit conversion from TraversableViewLike [A, Coll, This] to CollectionsHaveToParArray [TraversableViewLike [A, Coll, This], T] performed by method CollectionsHaveToParArray in scala.collection.parallel. This conversion will take place only if an implicit value of type (TraversableViewLike [A, Coll, This]) ⇒ GenTraversableOnce [T] is in scope.
• Definition Classes
  • CollectionsHaveToParArray (added by implicit convertion: scala.collection.parallel.CollectionsHaveToParArray)

Full Source:

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection

import generic._
import mutable.{ Builder, ArrayBuffer }
import scala.annotation.migration
import scala.language.implicitConversions

trait ViewMkString[+A] {
  self: Traversable[A] =>

  // It is necessary to use thisSeq rather than toSeq to avoid cycles in the
  // eager evaluation of vals in transformed view subclasses, see #4558.
  protected[this] def thisSeq: Seq[A] = (new ArrayBuffer[A] ++= self).result

  // Have to overload all three to work around #4299.  The overload
  // is because mkString should force a view but toString should not.
  override def mkString: String = mkString("")
  override def mkString(sep: String): String = mkString("", sep, "")
  override def mkString(start: String, sep: String, end: String): String = {
    thisSeq.addString(new StringBuilder(), start, sep, end).toString
  }
  override def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder = {
    var first = true
    b append start
    for (x <- self) {
      if (first) first = false else b append sep
      b append x
    }
    b append end
    b
  }
}

/** A template trait for non-strict views of traversable collections.
 *  $traversableViewInfo
 *
 *  Implementation note: Methods such as `map` or `flatMap` on this view will not invoke the implicitly passed
 *  `Builder` factory, but will return a new view directly, to preserve by-name behavior.
 *  The new view is then cast to the factory's result type. This means that every `CanBuildFrom`
 *  that takes a `View` as its `From` type parameter must yield the same view (or a generic
 *  superclass of it) as its result parameter. If that assumption is broken, cast errors might result.
 *
 *  @define viewInfo
 *  A view is a lazy version of some collection. Collection transformers such as
 *  `map` or `filter` or `++` do not traverse any elements when applied on a view.
 *  Instead they create a new view which simply records that fact that the operation
 *  needs to be applied. The collection elements are accessed, and the view operations are applied,
 *  when a non-view result is needed, or when the `force` method is called on a view.
 *  @define traversableViewInfo
 *  $viewInfo
 *
 *  All views for traversable collections are defined by creating a new `foreach` method.
 *
 *  @author Martin Odersky
 *  @version 2.8
 *  @since   2.8
 *  @tparam A    the element type of the view
 *  @tparam Coll the type of the underlying collection containing the elements.
 *  @tparam This the type of the view itself
 */
trait TraversableViewLike[+A,
                          +Coll,
                          +This <: TraversableView[A, Coll] with TraversableViewLike[A, Coll, This]]
  extends Traversable[A] with TraversableLike[A, This] with ViewMkString[A]
{
  self =>

  protected def underlying: Coll
  protected[this] def viewIdentifier: String = ""
  protected[this] def viewIdString: String = ""
  def viewToString = stringPrefix + viewIdString + "(...)"
  override def stringPrefix = "TraversableView"

  override protected[this] def newBuilder: Builder[A, This] =
    throw new UnsupportedOperationException(this+".newBuilder")

  def force[B >: A, That](implicit bf: CanBuildFrom[Coll, B, That]) = {
    val b = bf(underlying)
    b ++= this
    b.result()
  }

  /** Explicit instantiation of the `Transformed` trait to reduce class file size in subclasses. */
  private[collection] abstract class AbstractTransformed[+B] extends Traversable[B] with Transformed[B]


  /** The implementation base trait of this view.
   *  This trait and all its subtraits has to be re-implemented for each
   *  ViewLike class.
   */
  trait Transformed[+B] extends TraversableView[B, Coll] {
    def foreach[U](f: B => U): Unit

    lazy val underlying = self.underlying
    final override protected[this] def viewIdString = self.viewIdString + viewIdentifier

    // Methods whose standard implementations use "isEmpty" need to be rewritten
    // for views, else they will end up traversing twice in a situation like:
    //   xs.view.flatMap(f).headOption
    override def headOption: Option[B] = {
      for (x <- this)
        return Some(x)

      None
    }
    override def lastOption: Option[B] = {
      // (Should be) better than allocating a Some for every element.
      var empty = true
      var result: B = null.asInstanceOf[B]
      for (x <- this) {
        empty = false
        result = x
      }
      if (empty) None else Some(result)
    }

    // XXX: As yet not dealt with, tail and init both call isEmpty.
    override def stringPrefix = self.stringPrefix
    override def toString = viewToString
  }

  trait EmptyView extends Transformed[Nothing] {
    final override def isEmpty = true
    final override def foreach[U](f: Nothing => U): Unit = ()
  }

  /** A fall back which forces everything into a vector and then applies an operation
   *  on it. Used for those operations which do not naturally lend themselves to a view
   */
  trait Forced[B] extends Transformed[B] {
    protected[this] val forced: GenSeq[B]
    def foreach[U](f: B => U) = forced foreach f
    final override protected[this] def viewIdentifier = "C"
  }

  trait Sliced extends Transformed[A] {
    protected[this] val endpoints: SliceInterval
    protected[this] def from  = endpoints.from
    protected[this] def until = endpoints.until
    // protected def newSliced(_endpoints: SliceInterval): Transformed[A] =
    //   self.newSliced(endpoints.recalculate(_endpoints))

    def foreach[U](f: A => U) {
      var index = 0
      for (x <- self) {
        if (from <= index) {
          if (until <= index) return
          f(x)
        }
        index += 1
      }
    }
    final override protected[this] def viewIdentifier = "S"
  }

  trait Mapped[B] extends Transformed[B] {
    protected[this] val mapping: A => B
    def foreach[U](f: B => U) {
      for (x <- self)
        f(mapping(x))
    }
    final override protected[this] def viewIdentifier = "M"
  }

  trait FlatMapped[B] extends Transformed[B] {
    protected[this] val mapping: A => GenTraversableOnce[B]
    def foreach[U](f: B => U) {
      for (x <- self)
        for (y <- mapping(x).seq)
          f(y)
    }
    final override protected[this] def viewIdentifier = "N"
  }

  trait Appended[B >: A] extends Transformed[B] {
    protected[this] val rest: GenTraversable[B]
    def foreach[U](f: B => U) {
      self foreach f
      rest foreach f
    }
    final override protected[this] def viewIdentifier = "A"
  }
  
  trait Prepended[B >: A] extends Transformed[B] {
    protected[this] val fst: GenTraversable[B]
    def foreach[U](f: B => U) {
      fst foreach f
      self foreach f
    }
    final override protected[this] def viewIdentifier = "A"
  }

  trait Filtered extends Transformed[A] {
    protected[this] val pred: A => Boolean
    def foreach[U](f: A => U) {
      for (x <- self)
        if (pred(x)) f(x)
    }
    final override protected[this] def viewIdentifier = "F"
  }

  trait TakenWhile extends Transformed[A] {
    protected[this] val pred: A => Boolean
    def foreach[U](f: A => U) {
      for (x <- self) {
        if (!pred(x)) return
        f(x)
      }
    }
    final override protected[this] def viewIdentifier = "T"
  }

  trait DroppedWhile extends Transformed[A] {
    protected[this] val pred: A => Boolean
    def foreach[U](f: A => U) {
      var go = false
      for (x <- self) {
        if (!go && !pred(x)) go = true
        if (go) f(x)
      }
    }
    final override protected[this] def viewIdentifier = "D"
  }

  override def ++[B >: A, That](xs: GenTraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That =
    newAppended(xs.seq.toTraversable).asInstanceOf[That]
  
  override def ++:[B >: A, That](xs: TraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That = 
    newPrepended(xs.seq.toTraversable).asInstanceOf[That]
    
  // Need second one because of optimization in TraversableLike
  override def ++:[B >: A, That](xs: Traversable[B])(implicit bf: CanBuildFrom[This, B, That]): That = 
    newPrepended(xs).asInstanceOf[That]

  override def map[B, That](f: A => B)(implicit bf: CanBuildFrom[This, B, That]): That = {
    newMapped(f).asInstanceOf[That]
//    val b = bf(repr)
//          if (b.isInstanceOf[NoBuilder[_]]) newMapped(f).asInstanceOf[That]
//    else super.map[B, That](f)(bf)
  }

  override def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[This, B, That]): That =
    filter(pf.isDefinedAt).map(pf)(bf)

  override def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[This, B, That]): That = {
    newFlatMapped(f).asInstanceOf[That]
// was:    val b = bf(repr)
//     if (b.isInstanceOf[NoBuilder[_]]) newFlatMapped(f).asInstanceOf[That]
//    else super.flatMap[B, That](f)(bf)
  }
  override def flatten[B](implicit asTraversable: A => /*<:<!!!*/ GenTraversableOnce[B]) =
    newFlatMapped(asTraversable)
  private[this] implicit def asThis(xs: Transformed[A]): This = xs.asInstanceOf[This]

  /** Boilerplate method, to override in each subclass
   *  This method could be eliminated if Scala had virtual classes
   */
  protected def newForced[B](xs: => GenSeq[B]): Transformed[B] = new { val forced = xs } with AbstractTransformed[B] with Forced[B]
  protected def newAppended[B >: A](that: GenTraversable[B]): Transformed[B] = new { val rest = that } with AbstractTransformed[B] with Appended[B]
  protected def newPrepended[B >: A](that: GenTraversable[B]): Transformed[B] = new { val fst = that } with AbstractTransformed[B] with Prepended[B]
  protected def newMapped[B](f: A => B): Transformed[B] = new { val mapping = f } with AbstractTransformed[B] with Mapped[B]
  protected def newFlatMapped[B](f: A => GenTraversableOnce[B]): Transformed[B] = new { val mapping = f } with AbstractTransformed[B] with FlatMapped[B]
  protected def newFiltered(p: A => Boolean): Transformed[A] = new { val pred = p } with AbstractTransformed[A] with Filtered
  protected def newSliced(_endpoints: SliceInterval): Transformed[A] = new { val endpoints = _endpoints } with AbstractTransformed[A] with Sliced
  protected def newDroppedWhile(p: A => Boolean): Transformed[A] = new { val pred = p } with AbstractTransformed[A] with DroppedWhile
  protected def newTakenWhile(p: A => Boolean): Transformed[A] = new { val pred = p } with AbstractTransformed[A] with TakenWhile

  protected def newTaken(n: Int): Transformed[A] = newSliced(SliceInterval(0, n))
  protected def newDropped(n: Int): Transformed[A] = newSliced(SliceInterval(n, Int.MaxValue))

  override def filter(p: A => Boolean): This = newFiltered(p)
  override def withFilter(p: A => Boolean): This = newFiltered(p)
  override def partition(p: A => Boolean): (This, This) = (newFiltered(p), newFiltered(!p(_)))
  override def init: This = newSliced(SliceInterval(0, size - 1)) // !!! can't call size here.
  override def drop(n: Int): This = newDropped(n)
  override def take(n: Int): This = newTaken(n)
  override def slice(from: Int, until: Int): This = newSliced(SliceInterval(from, until))
  override def dropWhile(p: A => Boolean): This = newDroppedWhile(p)
  override def takeWhile(p: A => Boolean): This = newTakenWhile(p)
  override def span(p: A => Boolean): (This, This) = (newTakenWhile(p), newDroppedWhile(p))
  override def splitAt(n: Int): (This, This) = (newTaken(n), newDropped(n))

  override def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[This, B, That]): That =
    newForced(thisSeq.scanLeft(z)(op)).asInstanceOf[That]

  @migration("The behavior of `scanRight` has changed. The previous behavior can be reproduced with scanRight.reverse.", "2.9.0")
  override def scanRight[B, That](z: B)(op: (A, B) => B)(implicit bf: CanBuildFrom[This, B, That]): That =
    newForced(thisSeq.scanRight(z)(op)).asInstanceOf[That]

  override def groupBy[K](f: A => K): immutable.Map[K, This] =
    thisSeq groupBy f mapValues (xs => newForced(xs))

  override def unzip[A1, A2](implicit asPair: A => (A1, A2)) =
    (newMapped(x => asPair(x)._1), newMapped(x => asPair(x)._2))  // TODO - Performance improvements.

  override def unzip3[A1, A2, A3](implicit asTriple: A => (A1, A2, A3)) =
    (newMapped(x => asTriple(x)._1), newMapped(x => asTriple(x)._2), newMapped(x => asTriple(x)._3))  // TODO - Performance improvements.

  override def filterNot(p: (A) => Boolean): This =
    newFiltered(a => !(p(a)))

  override def inits: Iterator[This] =
    thisSeq.inits.map(as => newForced(as).asInstanceOf[This])

  override def tails: Iterator[This] =
    thisSeq.tails.map(as => newForced(as).asInstanceOf[This])

  override def tail: This =
    // super.tail would also work as it is currently implemented in terms of drop(Int).
    if (isEmpty) super.tail else newDropped(1)

  override def toString = viewToString
}