Scala Standard Library2.12.21 < Back
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# Packages

-  package root

  This is the documentation for the Scala standard library.

  This is the documentation for the Scala standard library.

  #### Package structure

  The scala package contains core types like `Int`, `Float`, `Array` or `Option` which are accessible in all Scala compilation units without explicit qualification or imports.

  Notable packages include:

  - `scala.collection` and its sub-packages contain Scala's collections framework
    - `scala.collection.immutable` - Immutable, sequential data-structures such as `Vector`, `List`, `Range`, `HashMap` or `HashSet`
    - `scala.collection.mutable` - Mutable, sequential data-structures such as `ArrayBuffer`, `StringBuilder`, `HashMap` or `HashSet`
    - `scala.collection.concurrent` - Mutable, concurrent data-structures such as `TrieMap`
    - `scala.collection.parallel.immutable` - Immutable, parallel data-structures such as `ParVector`, `ParRange`, `ParHashMap` or `ParHashSet`
    - `scala.collection.parallel.mutable` - Mutable, parallel data-structures such as `ParArray`, `ParHashMap`, `ParTrieMap` or `ParHashSet`
  - `scala.concurrent` - Primitives for concurrent programming such as `Futures` and `Promises`
  - `scala.io` - Input and output operations
  - `scala.math` - Basic math functions and additional numeric types like `BigInt` and `BigDecimal`
  - `scala.sys` - Interaction with other processes and the operating system
  - `scala.util.matching` - Regular expressions

  Other packages exist. See the complete list on the right.

  Additional parts of the standard library are shipped as separate libraries. These include:

  - `scala.reflect` - Scala's reflection API (scala-reflect.jar)
  - `scala.xml` - XML parsing, manipulation, and serialization (scala-xml.jar)
  - `scala.swing` - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)
  - `scala.util.parsing` - Parser combinators (scala-parser-combinators.jar)

  #### Automatic imports

  Identifiers in the scala package and the `scala.Predef` object are always in scope by default.

  Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, `List` is an alias for `scala.collection.immutable.List`.

  Other aliases refer to classes provided by the underlying platform. For example, on the JVM, `String` is an alias for `java.lang.String`.

  Definition Classes
    root
-  package scala

  Core Scala types.

  Core Scala types. They are always available without an explicit import.

  Definition Classes
    root
-  package collection

  Contains the base traits and objects needed to use and extend Scala's collection library.

  Contains the base traits and objects needed to use and extend Scala's collection library.

  #### Guide

  A detailed guide for using the collections library is available at http://docs.scala-lang.org/overviews/collections/introduction.html. Developers looking to extend the collections library can find a description of its architecture at http://docs.scala-lang.org/overviews/core/architecture-of-scala-collections.html.

  #### Using Collections

  It is convenient to treat all collections as either a scala.collection.Traversable or scala.collection.Iterable, as these traits define the vast majority of operations on a collection.

  Collections can, of course, be treated as specifically as needed, and the library is designed to ensure that the methods that transform collections will return a collection of the same type:

      scala> val array = Array(1,2,3,4,5,6)
      array: Array[Int] = Array(1, 2, 3, 4, 5, 6)

      scala> array map { _.toString }
      res0: Array[String] = Array(1, 2, 3, 4, 5, 6)

      scala> val list = List(1,2,3,4,5,6)
      list: List[Int] = List(1, 2, 3, 4, 5, 6)

      scala> list map { _.toString }
      res1: List[String] = List(1, 2, 3, 4, 5, 6)

  #### Creating Collections

  The most common way to create a collection is to use its companion object as a factory. The three most commonly used collections are scala.collection.Seq, scala.collection.immutable.Set, and scala.collection.immutable.Map. They can be used directly as shown below since their companion objects are all available as type aliases in either the scala package or in `scala.Predef`. New collections are created like this:

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

      scala> val set = Set(1,2,3,4,1)
      set: scala.collection.immutable.Set[Int] = Set(1, 2, 3, 4)

      scala> val map = Map(1 -> "one", 2 -> "two", 3 -> "three", 2 -> "too")
      map: scala.collection.immutable.Map[Int,String] = Map(1 -> one, 2 -> too, 3 -> three)

  It is also typical to prefer the scala.collection.immutable collections over those in scala.collection.mutable; the types aliased in the `scala.Predef` object are the immutable versions.

  Also note that the collections library was carefully designed to include several implementations of each of the three basic collection types. These implementations have specific performance characteristics which are described in the guide.

  The concrete parallel collections also have specific performance characteristics which are described in the parallel collections guide

  ##### Converting to and from Java Collections

  The scala.collection.JavaConverters object provides a collection of decorators that allow converting between Scala and Java collections using `asScala` and `asJava` methods.

  Definition Classes
    scala
-  package parallel

  Package object for parallel collections.

  Package object for parallel collections.

  Definition Classes
    collection
-  trait ParIterableLike[+T, +Repr <: ParIterable[T], +Sequential <: scala.Iterable[T] with IterableLike[T, Sequential]] extends GenIterableLike[T, Repr] with CustomParallelizable[T, Repr] with Parallel with HasNewCombiner[T, Repr]

  A template trait for parallel collections of type `ParIterable[T]`.

  A template trait for parallel collections of type `ParIterable[T]`.

  This is a base trait for Scala parallel collections. It defines behaviour common to all parallel collections. Concrete parallel collections should inherit this trait and `ParIterable` if they want to define specific combiner factories.

  Parallel operations are implemented with divide and conquer style algorithms that parallelize well. The basic idea is to split the collection into smaller parts until they are small enough to be operated on sequentially.

  All of the parallel operations are implemented as tasks within this trait. Tasks rely on the concept of splitters, which extend iterators. Every parallel collection defines:

      def splitter: IterableSplitter[T]

  which returns an instance of `IterableSplitter[T]`, which is a subtype of `Splitter[T]`. Splitters have a method `remaining` to check the remaining number of elements, and method `split` which is defined by splitters. Method `split` divides the splitters iterate over into disjunct subsets:

      def split: Seq[Splitter]

  which splits the splitter into a sequence of disjunct subsplitters. This is typically a very fast operation which simply creates wrappers around the receiver collection. This can be repeated recursively.

  Tasks are scheduled for execution through a scala.collection.parallel.TaskSupport object, which can be changed through the `tasksupport` setter of the collection.

  Method `newCombiner` produces a new combiner. Combiners are an extension of builders. They provide a method `combine` which combines two combiners and returns a combiner containing elements of both combiners. This method can be implemented by aggressively copying all the elements into the new combiner or by lazily binding their results. It is recommended to avoid copying all of the elements for performance reasons, although that cost might be negligible depending on the use case. Standard parallel collection combiners avoid copying when merging results, relying either on a two-step lazy construction or specific data-structure properties.

  Methods:

      def seq: Sequential
      def par: Repr

  produce the sequential or parallel implementation of the collection, respectively. Method `par` just returns a reference to this parallel collection. Method `seq` is efficient - it will not copy the elements. Instead, it will create a sequential version of the collection using the same underlying data structure. Note that this is not the case for sequential collections in general - they may copy the elements and produce a different underlying data structure.

  The combination of methods `toMap`, `toSeq` or `toSet` along with `par` and `seq` is a flexible way to change between different collection types.

  Since this trait extends the `GenIterable` trait, methods like `size` must also be implemented in concrete collections, while `iterator` forwards to `splitter` by default.

  Each parallel collection is bound to a specific fork/join pool, on which dormant worker threads are kept. The fork/join pool contains other information such as the parallelism level, that is, the number of processors used. When a collection is created, it is assigned the default fork/join pool found in the `scala.parallel` package object.

  Parallel collections are not necessarily ordered in terms of the `foreach` operation (see `Traversable`). Parallel sequences have a well defined order for iterators - creating an iterator and traversing the elements linearly will always yield the same order. However, bulk operations such as `foreach`, `map` or `filter` always occur in undefined orders for all parallel collections.

  Existing parallel collection implementations provide strict parallel iterators. Strict parallel iterators are aware of the number of elements they have yet to traverse. It's also possible to provide non-strict parallel iterators, which do not know the number of elements remaining. To do this, the new collection implementation must override `isStrictSplitterCollection` to `false`. This will make some operations unavailable.

  To create a new parallel collection, extend the `ParIterable` trait, and implement `size`, `splitter`, `newCombiner` and `seq`. Having an implicit combiner factory requires extending this trait in addition, as well as providing a companion object, as with regular collections.

  Method `size` is implemented as a constant time operation for parallel collections, and parallel collection operations rely on this assumption.

  The higher-order functions passed to certain operations may contain side-effects. Since implementations of bulk operations may not be sequential, this means that side-effects may not be predictable and may produce data-races, deadlocks or invalidation of state if care is not taken. It is up to the programmer to either avoid using side-effects or to use some form of synchronization when accessing mutable data.

  T

    the element type of the collection

  Repr

    the type of the actual collection containing the elements

  Definition Classes
    parallel
- Accessor
- Aggregate
- BuilderOps
- Collect
- Composite
- Copy
- CopyToArray
- Count
- CreateScanTree
- Drop
- Exists
- Filter
- FilterNot
- Find
- FlatMap
- Fold
- Forall
- Foreach
- FromScanTree
- GroupBy
- Map
- Max
- Min
- NonDivisible
- NonDivisibleTask
- ParComposite
- Partition
- Product
- Reduce
- ResultMapping
- ScanLeaf
- ScanNode
- ScanTree
- SeqComposite
- SignallingOps
- Slice
- Span
- SplitAt
- StrictSplitterCheckTask
- Sum
- Take
- TakeWhile
- TaskOps
- ToParCollection
- ToParMap
- Transformer
- Zip
- ZipAll

c

scala.collection.parallel.ParIterableLike

# SeqComposite 

###

#### abstract class SeqComposite[FR, SR, R, First <: StrictSplitterCheckTask[FR, _], Second <: StrictSplitterCheckTask[SR, _]] extends Composite[FR, SR, R, First, Second]

Sequentially performs one task after another.

Attributes
  protected[this]
Source
  ParIterableLike.scala

Linear Supertypes
Composite[FR, SR, R, First, Second], NonDivisibleTask[R, Composite[FR, SR, R, First, Second]], StrictSplitterCheckTask[R, Composite[FR, SR, R, First, Second]], Task[R, Composite[FR, SR, R, First, Second]], AnyRef, Any
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Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. SeqComposite
2. Composite
3. NonDivisibleTask
4. StrictSplitterCheckTask
5. Task
6. AnyRef
7. Any

Implicitly

1. by CollectionsHaveToParArray
2. by any2stringadd
3. by StringFormat
4. by Ensuring
5. by ArrowAssoc

1. Hide All
2. Show All

Visibility

1. Public
2. All

### Instance Constructors

1.  new SeqComposite(f: First, s: Second)

### Type Members

1.  type Result = R
   Definition Classes
     Task

### Abstract Value Members

1.  abstract def combineResults(fr: FR, sr: SR): R
   Definition Classes
     Composite

### Concrete Value Members

1.  final def !=(arg0: Any): Boolean

   Test two objects for inequality.

   Test two objects for inequality.

   returns

     `true` if !(this == that), false otherwise.

   Definition Classes
     AnyRef → Any
2.  final def ##(): Int

   Equivalent to `x.hashCode` except for boxed numeric types and `null`.

   Equivalent to `x.hashCode` except for boxed numeric types and `null`. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For `null` returns a hashcode where `null.hashCode` throws a `NullPointerException`.

   returns

     a hash value consistent with ==

   Definition Classes
     AnyRef → Any
3.  def +(other: String): String
   Implicit
     This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to any2stringadd[SeqComposite[FR, SR, R, First, Second]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (SeqComposite[FR, SR, R, First, Second], B)
   Implicit
     This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to ArrowAssoc[SeqComposite[FR, SR, R, First, Second]] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()
5.  final def ==(arg0: Any): Boolean

   The expression `x == that` is equivalent to `if (x eq null) that eq null else x.equals(that)`.

   The expression `x == that` is equivalent to `if (x eq null) that eq null else x.equals(that)`.

   returns

     `true` if the receiver object is equivalent to the argument; `false` otherwise.

   Definition Classes
     AnyRef → Any
6.  final def asInstanceOf[T0]: T0

   Cast the receiver object to be of type `T0`.

   Cast the receiver object to be of type `T0`.

   Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression `1.asInstanceOf[String]` will throw a `ClassCastException` at runtime, while the expression `List(1).asInstanceOf[List[String]]` will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

   returns

     the receiver object.

   Definition Classes
     Any
   Exceptions thrown

     `ClassCastException` if the receiver object is not an instance of the erasure of type `T0`.

7.  def clone(): AnyRef

   Create a copy of the receiver object.

   Create a copy of the receiver object.

   The default implementation of the `clone` method is platform dependent.

   returns

     a copy of the receiver object.

   Attributes
     protected[lang]
   Definition Classes
     AnyRef
   Annotations
     @throws( ... ) @native()
   Note

     not specified by SLS as a member of AnyRef

8.  def ensuring(cond: (SeqComposite[FR, SR, R, First, Second]) ⇒ Boolean, msg: ⇒ Any): SeqComposite[FR, SR, R, First, Second]
   Implicit
     This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to Ensuring[SeqComposite[FR, SR, R, First, Second]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
9.  def ensuring(cond: (SeqComposite[FR, SR, R, First, Second]) ⇒ Boolean): SeqComposite[FR, SR, R, First, Second]
   Implicit
     This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to Ensuring[SeqComposite[FR, SR, R, First, Second]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: Boolean, msg: ⇒ Any): SeqComposite[FR, SR, R, First, Second]
    Implicit
      This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to Ensuring[SeqComposite[FR, SR, R, First, Second]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def ensuring(cond: Boolean): SeqComposite[FR, SR, R, First, Second]
    Implicit
      This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to Ensuring[SeqComposite[FR, SR, R, First, Second]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
12.  final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (`that`) is a reference to the receiver object (`this`).

    Tests whether the argument (`that`) is a reference to the receiver object (`this`).

    The `eq` method implements an equivalence relation on non-null instances of `AnyRef`, and has three additional properties:

    - It is consistent: for any non-null instances `x` and `y` of type `AnyRef`, multiple invocations of `x.eq(y)` consistently returns `true` or consistently returns `false`.
    - For any non-null instance `x` of type `AnyRef`, `x.eq(null)` and `null.eq(x)` returns `false`.
    - `null.eq(null)` returns `true`.

    When overriding the `equals` or `hashCode` methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (`o1 eq o2`), they should be equal to each other (`o1 == o2`) and they should hash to the same value (`o1.hashCode == o2.hashCode`).

    returns

      `true` if the argument is a reference to the receiver object; `false` otherwise.

    Definition Classes
      AnyRef
13.  def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. Default implementation delegates to `eq`.

    See also `equals` in scala.Any.

    returns

      `true` if the receiver object is equivalent to the argument; `false` otherwise.

    Definition Classes
      AnyRef → Any
14.  def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

    Called by the garbage collector on the receiver object when there are no more references to the object.

    The details of when and if the `finalize` method is invoked, as well as the interaction between `finalize` and non-local returns and exceptions, are all platform dependent.

    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )
    Note

      not specified by SLS as a member of AnyRef

15.  def forwardThrowable(): Unit
    Definition Classes
      Task
16.  val ft: First
    Definition Classes
      Composite
17.  final def getClass(): Class[_]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

      a class object corresponding to the runtime type of the receiver.

    Definition Classes
      AnyRef → Any
    Annotations
      @native()
18.  def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in scala.Any.

    returns

      the hash code value for this object.

    Definition Classes
      AnyRef → Any
    Annotations
      @native()
19.  final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is `T0`.

    Test whether the dynamic type of the receiver object is `T0`.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression `1.isInstanceOf[String]` will return `false`, while the expression `List(1).isInstanceOf[List[String]]` will return `true`. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

      `true` if the receiver object is an instance of erasure of type `T0`; `false` otherwise.

    Definition Classes
      Any
20.  def leaf(prevr: Option[R]): Unit

    Body of the task - non-divisible unit of work done by this task.

    Body of the task - non-divisible unit of work done by this task. Optionally is provided with the result from the previous completed task or `None` if there was no previous task (or the previous task is uncompleted or unknown).

    Definition Classes
      SeqComposite → Task
21.  def mergeSubtasks(): Unit
    Attributes
      protected
    Definition Classes
      Composite
22.  final def ne(arg0: AnyRef): Boolean

    Equivalent to `!(this eq that)`.

    Equivalent to `!(this eq that)`.

    returns

      `true` if the argument is not a reference to the receiver object; `false` otherwise.

    Definition Classes
      AnyRef
23.  final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
      AnyRef
    Annotations
      @native()
    Note

      not specified by SLS as a member of AnyRef

24.  final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
      AnyRef
    Annotations
      @native()
    Note

      not specified by SLS as a member of AnyRef

25.  def repr: Composite[FR, SR, R, First, Second]
    Definition Classes
      Task
26.  def requiresStrictSplitters: Boolean
    Definition Classes
      Composite → StrictSplitterCheckTask
27.  var result: R

    A result that can be accessed once the task is completed.

    A result that can be accessed once the task is completed.

    Definition Classes
      Composite → Task
28.  def shouldSplitFurther: Boolean

    Decides whether or not this task should be split further.

    Decides whether or not this task should be split further.

    Definition Classes
      NonDivisibleTask → Task
29.  def split: Nothing

    Splits this task into a list of smaller tasks.

    Splits this task into a list of smaller tasks.

    Definition Classes
      NonDivisibleTask → Task
30.  val st: Second
    Definition Classes
      Composite
31.  final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
      AnyRef
32.  val throwable: Throwable
    Definition Classes
      Task
    Annotations
      @volatile()
33.  def toParArray: ParArray[T]
    Implicit
      This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to CollectionsHaveToParArray[SeqComposite[FR, SR, R, First, Second], T] performed by method CollectionsHaveToParArray in scala.collection.parallel. This conversion will take place only if an implicit value of type (SeqComposite[FR, SR, R, First, Second]) ⇒ GenTraversableOnce[T] is in scope.
    Definition Classes
      CollectionsHaveToParArray
34.  def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

      a String representation of the object.

    Definition Classes
      AnyRef → Any
35.  final def wait(): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
36.  final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... )
37.  final def wait(arg0: Long): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws( ... ) @native()
38.  def →[B](y: B): (SeqComposite[FR, SR, R, First, Second], B)
    Implicit
      This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to ArrowAssoc[SeqComposite[FR, SR, R, First, Second]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Deprecated Value Members

1.  def formatted(fmtstr: String): String

   Returns string formatted according to given `format` string.

   Returns string formatted according to given `format` string. Format strings are as for `String.format` (@see java.lang.String.format).

   Implicit
     This member is added by an implicit conversion from SeqComposite[FR, SR, R, First, Second] to StringFormat[SeqComposite[FR, SR, R, First, Second]] performed by method StringFormat in scala.Predef.
   Definition Classes
     StringFormat
   Annotations
     @deprecated @inline()
   Deprecated

     (Since version 2.12.16) Use `formatString.format(value)` instead of `value.formatted(formatString)`, or use the `f""` string interpolator. In Java 15 and later, `formatted` resolves to the new method in String which has reversed parameters.

### Inherited from Composite[FR, SR, R, First, Second]

### Inherited from NonDivisibleTask[R, Composite[FR, SR, R, First, Second]]

### Inherited from StrictSplitterCheckTask[R, Composite[FR, SR, R, First, Second]]

### Inherited from Task[R, Composite[FR, SR, R, First, Second]]

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion CollectionsHaveToParArray from SeqComposite[FR, SR, R, First, Second] to CollectionsHaveToParArray[SeqComposite[FR, SR, R, First, Second], T]

### Inherited by implicit conversion any2stringadd from SeqComposite[FR, SR, R, First, Second] to any2stringadd[SeqComposite[FR, SR, R, First, Second]]

### Inherited by implicit conversion StringFormat from SeqComposite[FR, SR, R, First, Second] to StringFormat[SeqComposite[FR, SR, R, First, Second]]

### Inherited by implicit conversion Ensuring from SeqComposite[FR, SR, R, First, Second] to Ensuring[SeqComposite[FR, SR, R, First, Second]]

### Inherited by implicit conversion ArrowAssoc from SeqComposite[FR, SR, R, First, Second] to ArrowAssoc[SeqComposite[FR, SR, R, First, Second]]

### Ungrouped