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 annotation
  Definition Classes
    scala
-  package beans
  Definition Classes
    scala
-  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 compat
  Definition Classes
    scala
-  package concurrent

  This package object contains primitives for concurrent and parallel programming.

  This package object contains primitives for concurrent and parallel programming.

  #### Guide

  A more detailed guide to Futures and Promises, including discussion and examples can be found at http://docs.scala-lang.org/overviews/core/futures.html.

  #### Common Imports

  When working with Futures, you will often find that importing the whole concurrent package is convenient:

      import scala.concurrent._

  When using things like `Future`s, it is often required to have an implicit `ExecutionContext` in scope. The general advice for these implicits are as follows.

  If the code in question is a class or method definition, and no `ExecutionContext` is available, request one from the caller by adding an implicit parameter list:

      def myMethod(myParam: MyType)(implicit ec: ExecutionContext) = …
      //Or
      class MyClass(myParam: MyType)(implicit ec: ExecutionContext) { … }

  This allows the caller of the method, or creator of the instance of the class, to decide which `ExecutionContext` should be used.

  For typical REPL usage and experimentation, importing the global `ExecutionContext` is often desired.

      import scala.concurrent.ExcutionContext.Implicits.global

  #### Specifying Durations

  Operations often require a duration to be specified. A duration DSL is available to make defining these easier:

      import scala.concurrent.duration._
      val d: Duration = 10.seconds

  #### Using Futures For Non-blocking Computation

  Basic use of futures is easy with the factory method on Future, which executes a provided function asynchronously, handing you back a future result of that function without blocking the current thread. In order to create the Future you will need either an implicit or explicit ExecutionContext to be provided:

      import scala.concurrent._
      import ExecutionContext.Implicits.global  // implicit execution context

      val firstZebra: Future[Int] = Future {
        val source = scala.io.Source.fromFile("/etc/dictionaries-common/words")
        source.toSeq.indexOfSlice("zebra")
      }

  #### Avoid Blocking

  Although blocking is possible in order to await results (with a mandatory timeout duration):

      import scala.concurrent.duration._
      Await.result(firstZebra, 10.seconds)

  and although this is sometimes necessary to do, in particular for testing purposes, blocking in general is discouraged when working with Futures and concurrency in order to avoid potential deadlocks and improve performance. Instead, use callbacks or combinators to remain in the future domain:

      val animalRange: Future[Int] = for {
        aardvark <- firstAardvark
        zebra <- firstZebra
      } yield zebra - aardvark

      animalRange.onSuccess {
        case x if x > 500000 => println("It's a long way from Aardvark to Zebra")
      }

  Definition Classes
    scala
-  package io
  Definition Classes
    scala
-  package math

  The package object `scala.math` contains methods for performing basic numeric operations such as elementary exponential, logarithmic, root and trigonometric functions.

  The package object `scala.math` contains methods for performing basic numeric operations such as elementary exponential, logarithmic, root and trigonometric functions.

  All methods forward to java.lang.Math unless otherwise noted.

  Definition Classes
    scala
  See also

    java.lang.Math

-  package ref
  Definition Classes
    scala
-  package reflect
  Definition Classes
    scala
-  package runtime
  Definition Classes
    scala
-  package sys

  The package object `scala.sys` contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.

  The package object `scala.sys` contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.

  Definition Classes
    scala
  Since

    2.9

-  package text
  Definition Classes
    scala
-  package util
  Definition Classes
    scala
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t

scala

# Product1 

###
Companion object Product1

#### trait Product1[+T1] extends Product

Product1 is a Cartesian product of 1 component.

Source
  Product1.scala
Since

  2.3

Linear Supertypes
Product, Equals, Any
Known Subclasses
Tuple1
 
Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. Product1
2. Product
3. Equals
4. Any

Implicitly

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

1. Hide All
2. Show All

Visibility

1. Public
2. All

### Abstract Value Members

1.  abstract def _1: T1

   A projection of element 1 of this Product.

   A projection of element 1 of this Product.

   returns

     A projection of element 1.

2.  abstract def canEqual(that: Any): Boolean

   A method that should be called from every well-designed equals method that is open to be overridden in a subclass.

   A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

   that

     the value being probed for possible equality

   returns

     true if this instance can possibly equal `that`, otherwise false

   Definition Classes
     Equals
3.  abstract 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
     Any

### 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
     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
     Any
3.  def +(other: String): String
   Implicit
     This member is added by an implicit conversion from Product1[T1] to any2stringadd[Product1[T1]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (Product1[T1], B)
   Implicit
     This member is added by an implicit conversion from Product1[T1] to ArrowAssoc[Product1[T1]] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()
5.  final def ==(arg0: Any): Boolean

   Test two objects for equality.

   Test two objects for equality. 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
     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 ensuring(cond: (Product1[T1]) ⇒ Boolean, msg: ⇒ Any): Product1[T1]
   Implicit
     This member is added by an implicit conversion from Product1[T1] to Ensuring[Product1[T1]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
8.  def ensuring(cond: (Product1[T1]) ⇒ Boolean): Product1[T1]
   Implicit
     This member is added by an implicit conversion from Product1[T1] to Ensuring[Product1[T1]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
9.  def ensuring(cond: Boolean, msg: ⇒ Any): Product1[T1]
   Implicit
     This member is added by an implicit conversion from Product1[T1] to Ensuring[Product1[T1]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: Boolean): Product1[T1]
    Implicit
      This member is added by an implicit conversion from Product1[T1] to Ensuring[Product1[T1]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def equals(arg0: Any): Boolean

    Compares the receiver object (`this`) with the argument object (`that`) for equivalence.

    Compares the receiver object (`this`) with the argument object (`that`) for equivalence.

    Any implementation of this method should be an equivalence relation:

    - It is reflexive: for any instance `x` of type `Any`, `x.equals(x)` should return `true`.
    - It is symmetric: for any instances `x` and `y` of type `Any`, `x.equals(y)` should return `true` if and only if `y.equals(x)` returns `true`.
    - It is transitive: for any instances `x`, `y`, and `z` of type `Any` if `x.equals(y)` returns `true` and `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.

    If you override this method, you should verify that your implementation remains an equivalence relation. Additionally, when overriding this method it is usually necessary to override `hashCode` to ensure that objects which are "equal" (`o1.equals(o2)` returns `true`) hash to the same scala.Int. (`o1.hashCode.equals(o2.hashCode)`).

    returns

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

    Definition Classes
      Any
12.  def hashCode(): Int

    Calculate a hash code value for the object.

    Calculate a hash code value for the object.

    The default hashing algorithm is platform dependent.

    Note that it is allowed for two objects to have identical hash codes (`o1.hashCode.equals(o2.hashCode)`) yet not be equal (`o1.equals(o2)` returns `false`). A degenerate implementation could always return `0`. However, it is required that if two objects are equal (`o1.equals(o2)` returns `true`) that they have identical hash codes (`o1.hashCode.equals(o2.hashCode)`). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the `equals` method.

    returns

      the hash code value for this object.

    Definition Classes
      Any
13.  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
14.  def productArity: Int

    The arity of this product.

    The arity of this product.

    returns

      1

    Definition Classes
      Product1 → Product
15.  def productElement(n: Int): Any

    Returns the n-th projection of this product if 0 <= n < productArity, otherwise throws an `IndexOutOfBoundsException`.

    Returns the n-th projection of this product if 0 <= n < productArity, otherwise throws an `IndexOutOfBoundsException`.

    n

      number of the projection to be returned

    returns

      same as `._(n+1)`, for example `productElement(0)` is the same as `._1`.

    Definition Classes
      Product1 → Product
    Annotations
      @throws( clazz = classOf[IndexOutOfBoundsException] )
    Exceptions thrown
16.  def productIterator: Iterator[Any]

    An iterator over all the elements of this product.

    An iterator over all the elements of this product.

    returns

      in the default implementation, an `Iterator[Any]`

    Definition Classes
      Product
17.  def productPrefix: String

    A string used in the `toString` methods of derived classes.

    A string used in the `toString` methods of derived classes. Implementations may override this method to prepend a string prefix to the result of `toString` methods.

    returns

      in the default implementation, the empty string

    Definition Classes
      Product
18.  def toString(): String

    Returns a string representation of the object.

    Returns a string representation of the object.

    The default representation is platform dependent.

    returns

      a string representation of the object.

    Definition Classes
      Any
19.  def →[B](y: B): (Product1[T1], B)
    Implicit
      This member is added by an implicit conversion from Product1[T1] to ArrowAssoc[Product1[T1]] 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 Product1[T1] to StringFormat[Product1[T1]] 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 Product

### Inherited from Equals

### Inherited from Any

### Inherited by implicit conversion any2stringadd from Product1[T1] to any2stringadd[Product1[T1]]

### Inherited by implicit conversion StringFormat from Product1[T1] to StringFormat[Product1[T1]]

### Inherited by implicit conversion Ensuring from Product1[T1] to Ensuring[Product1[T1]]

### Inherited by implicit conversion ArrowAssoc from Product1[T1] to ArrowAssoc[Product1[T1]]

### Ungrouped