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.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.collection.parallel - Parallel collections (scala-parallel-collections.jar)
  • scala.util.parsing - Parser combinators (scala-parser-combinators.jar)
  • scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.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 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

•  trait Ordering[T] extends Comparator[T] with PartialOrdering[T] with Serializable

  Ordering is a trait whose instances each represent a strategy for sorting instances of a type.

  Ordering is a trait whose instances each represent a strategy for sorting instances of a type.

  Ordering's companion object defines many implicit objects to deal with subtypes of AnyVal (e.g. Int, Double), String, and others.

  To sort instances by one or more member variables, you can take advantage of these built-in orderings using Ordering.by and Ordering.on:

  import scala.util.Sorting
  val pairs = Array(("a", 5, 2), ("c", 3, 1), ("b", 1, 3))
  
  // sort by 2nd element
  Sorting.quickSort(pairs)(Ordering.by[(String, Int, Int), Int](_._2))
  
  // sort by the 3rd element, then 1st
  Sorting.quickSort(pairs)(Ordering[(Int, String)].on(x => (x._3, x._1)))

  An Ordering[T] is implemented by specifying compare(a:T, b:T), which decides how to order two instances a and b. Instances of Ordering[T] can be used by things like scala.util.Sorting to sort collections like Array[T].

  For example:

  import scala.util.Sorting
  
  case class Person(name:String, age:Int)
  val people = Array(Person("bob", 30), Person("ann", 32), Person("carl", 19))
  
  // sort by age
  object AgeOrdering extends Ordering[Person] {
    def compare(a:Person, b:Person) = a.age compare b.age
  }
  Sorting.quickSort(people)(AgeOrdering)

  This trait and scala.math.Ordered both provide this same functionality, but in different ways. A type T can be given a single way to order itself by extending Ordered. Using Ordering, this same type may be sorted in many other ways. Ordered and Ordering both provide implicits allowing them to be used interchangeably.

  You can import scala.math.Ordering.Implicits to gain access to other implicit orderings.

  Definition Classes

  math

  Annotations

  @implicitNotFound()

  See also

  scala.math.Ordered, scala.util.Sorting

• OrderingOps

scala.math.Ordering

OrderingOps