scala

language

object language

The scala.language object controls the language features available to the programmer, as proposed in the SIP-18 document.

Each of these features has to be explicitly imported into the current scope to become available:

import language.postfixOps // or language._
List(1, 2, 3) reverse

The language features are:

Source
language.scala
Linear Supertypes
AnyRef, Any
Ordering
  1. Grouped
  2. Alphabetic
  3. By inheritance
Inherited
  1. language
  2. AnyRef
  3. Any
  1. Hide All
  2. Show all
Learn more about member selection
Visibility
  1. Public
  2. All

Value Members

  1. final def !=(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  2. final def !=(arg0: Any): Boolean

    Definition Classes
    Any
  3. final def ##(): Int

    Definition Classes
    AnyRef → Any
  4. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  5. final def ==(arg0: Any): Boolean

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

    Definition Classes
    Any
  7. def clone(): AnyRef

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  8. implicit lazy val dynamics: dynamics

    Where enabled, direct or indirect subclasses of trait scala.

    Where enabled, direct or indirect subclasses of trait scala.Dynamic can be defined. Unless dynamics is enabled, a definition of a class, trait, or object that has Dynamic as a base trait is rejected. Dynamic member selection of existing subclasses of trait Dynamic are unaffected; they can be used anywhere.

    Why introduce the feature? To enable flexible DSLs and convenient interfacing with dynamic languages.

    Why control it? Dynamic member selection can undermine static checkability of programs. Furthermore, dynamic member selection often relies on reflection, which is not available on all platforms.

  9. final def eq(arg0: AnyRef): Boolean

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

    Definition Classes
    AnyRef → Any
  11. implicit lazy val existentials: existentials

    Only where enabled, existential types that cannot be expressed as wildcard types can be written and are allowed in inferred types of values or return types of methods.

    Only where enabled, existential types that cannot be expressed as wildcard types can be written and are allowed in inferred types of values or return types of methods. Existential types with wildcard type syntax such as List[_], or Map[String, _] are not affected.

    Why keep the feature? Existential types are needed to make sense of Java’s wildcard types and raw types and the erased types of run-time values.

    Why control it? Having complex existential types in a code base usually makes application code very brittle, with a tendency to produce type errors with obscure error messages. Therefore, going overboard with existential types is generally perceived not to be a good idea. Also, complicated existential types might be no longer supported in a future simplification of the language.

  12. object experimental

    The experimental object contains features that have been recently added but have not been thoroughly tested in production yet.

  13. def finalize(): Unit

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  14. final def getClass(): Class[_]

    Definition Classes
    AnyRef → Any
  15. def hashCode(): Int

    Definition Classes
    AnyRef → Any
  16. implicit lazy val higherKinds: higherKinds

    Only where this flag is enabled, higher-kinded types can be written.

    Only where this flag is enabled, higher-kinded types can be written.

    Why keep the feature? Higher-kinded types enable the definition of very general abstractions such as functor, monad, or arrow. A significant set of advanced libraries relies on them. Higher-kinded types are also at the core of the scala-virtualized effort to produce high-performance parallel DSLs through staging.

    Why control it? Higher kinded types in Scala lead to a Turing-complete type system, where compiler termination is no longer guaranteed. They tend to be useful mostly for type-level computation and for highly generic design patterns. The level of abstraction implied by these design patterns is often a barrier to understanding for newcomers to a Scala codebase. Some syntactic aspects of higher-kinded types are hard to understand for the uninitiated and type inference is less effective for them than for normal types. Because we are not completely happy with them yet, it is possible that some aspects of higher-kinded types will change in future versions of Scala. So an explicit enabling also serves as a warning that code involving higher-kinded types might have to be slightly revised in the future.

  17. implicit lazy val implicitConversions: implicitConversions

    Only where enabled, definitions of implicit conversions are allowed.

    Only where enabled, definitions of implicit conversions are allowed. An implicit conversion is an implicit value of unary function type A => B, or an implicit method that has in its first parameter section a single, non-implicit parameter. Examples:

    implicit def stringToInt(s: String): Int = s.length
    implicit val conv = (s: String) => s.length
    implicit def listToX(xs: List[T])(implicit f: T => X): X = ...

    implicit values of other types are not affected, and neither are implicit classes.

    Why keep the feature? Implicit conversions are central to many aspects of Scala’s core libraries.

    Why control it? Implicit conversions are known to cause many pitfalls if over-used. And there is a tendency to over-use them because they look very powerful and their effects seem to be easy to understand. Also, in most situations using implicit parameters leads to a better design than implicit conversions.

  18. final def isInstanceOf[T0]: Boolean

    Definition Classes
    Any
  19. final def ne(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  20. final def notify(): Unit

    Definition Classes
    AnyRef
  21. final def notifyAll(): Unit

    Definition Classes
    AnyRef
  22. implicit lazy val postfixOps: postfixOps

    Only where enabled, postfix operator notation (expr op) will be allowed.

    Only where enabled, postfix operator notation (expr op) will be allowed.

    Why keep the feature? Several DSLs written in Scala need the notation.

    Why control it? Postfix operators interact poorly with semicolon inference. Most programmers avoid them for this reason.

  23. implicit lazy val reflectiveCalls: reflectiveCalls

    Only where enabled, accesses to members of structural types that need reflection are supported.

    Only where enabled, accesses to members of structural types that need reflection are supported. Reminder: A structural type is a type of the form Parents { Decls } where Decls contains declarations of new members that do not override any member in Parents. To access one of these members, a reflective call is needed.

    Why keep the feature? Structural types provide great flexibility because they avoid the need to define inheritance hierarchies a priori. Besides, their definition falls out quite naturally from Scala’s concept of type refinement.

    Why control it? Reflection is not available on all platforms. Popular tools such as ProGuard have problems dealing with it. Even where reflection is available, reflective dispatch can lead to surprising performance degradations.

  24. final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
    AnyRef
  25. def toString(): String

    Definition Classes
    AnyRef → Any
  26. final def wait(): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  27. final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  28. final def wait(arg0: Long): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

Inherited from AnyRef

Inherited from Any

Language Features

Experimental Language Features

Ungrouped