scala.runtime.AbstractPartialFunction

abstract class AbstractPartialFunction[-T1, +R] extends (T1) ⇒ R with PartialFunction[T1, R]

AbstractPartialFunction reformulates all operations of its supertrait PartialFunction in terms of isDefinedAt and applyOrElse .

This allows more efficient implementations in many cases:

  • optimized orElse method supports chained orElse in linear time, and with no slow-down if the orElse part is not needed.
  • optimized lift method helps to avoid double evaluation of pattern matchers & guards of partial function literals.

This trait is used as a basis for implementation of all partial function literals.

Concrete Value Members From scala.Function1

def compose[A](g: (A) ⇒ T1): (A) ⇒ R

Composes two instances of Function1 in a new Function1, with this function applied last.

  • A
    • the type to which function g can be applied
  • g
    • a function A => T1
  • returns
    • a new function f such that f(x) == apply(g(x))
  • Definition Classes
    • Function1
  • Annotations
    • @ unspecialized ()

(defined at scala.Function1)

Abstract Value Members From scala.PartialFunction

abstract def isDefinedAt(x: T1): Boolean

Checks if a value is contained in the function’s domain.

  • x
    • the value to test
  • returns
    • true , iff x is in the domain of this function, false otherwise.
  • Definition Classes
    • PartialFunction

(defined at scala.PartialFunction)

Concrete Value Members From scala.PartialFunction

def andThen[C](k: (R) ⇒ C): PartialFunction[T1, C]

Composes this partial function with a transformation function that gets applied to results of this partial function.

  • C
    • the result type of the transformation function.
  • k
    • the transformation function
  • returns
    • a partial function with the same domain as this partial function, which maps arguments x to k(this(x)) .
  • Definition Classes
    • PartialFunction → Function1

(defined at scala.PartialFunction)

def applyOrElse[A1 <: T1, B1 >: R](x: A1, default: (A1) ⇒ B1): B1

Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.

Note that expression pf.applyOrElse(x, default) is equivalent to

if(pf isDefinedAt x) pf(x) else default(x)

except that applyOrElse method can be implemented more efficiently. For all partial function literals the compiler generates an applyOrElse implementation which avoids double evaluation of pattern matchers and guards. This makes applyOrElse the basis for the efficient implementation for many operations and scenarios, such as:

  • combining partial functions into orElse / andThen chains does not lead to excessive apply / isDefinedAt evaluation
  • lift and unlift do not evaluate source functions twice on each invocation
  • runWith allows efficient imperative-style combining of partial functions with conditionally applied actions

For non-literal partial function classes with nontrivial isDefinedAt method it is recommended to override applyOrElse with custom implementation that avoids double isDefinedAt evaluation. This may result in better performance and more predictable behavior w.r.t. side effects.

  • x
    • the function argument
  • default
    • the fallback function
  • returns
    • the result of this function or fallback function application.
  • Definition Classes
    • PartialFunction
  • Since
    • 2.10

(defined at scala.PartialFunction)

def lift: (T1) ⇒ Option[R]

Turns this partial function into a plain function returning an Option result.

  • returns
    • a function that takes an argument x to Some(this(x)) if this is defined for x , and to None otherwise.
  • Definition Classes
    • PartialFunction
  • See also
    • Function.unlift

(defined at scala.PartialFunction)

def orElse[A1 <: T1, B1 >: R](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

  • A1
    • the argument type of the fallback function
  • B1
    • the result type of the fallback function
  • that
    • the fallback function
  • returns
    • a partial function which has as domain the union of the domains of this partial function and that . The resulting partial function takes x to this(x) where this is defined, and to that(x) where it is not.
  • Definition Classes
    • PartialFunction

(defined at scala.PartialFunction)

def runWith[U](action: (R) ⇒ U): (T1) ⇒ Boolean

Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.

Note that expression pf.runWith(action)(x) is equivalent to

if(pf isDefinedAt x) { action(pf(x)); true } else false

except that runWith is implemented via applyOrElse and thus potentially more efficient. Using runWith avoids double evaluation of pattern matchers and guards for partial function literals.

  • action
    • the action function
  • returns
    • a function which maps arguments x to isDefinedAt(x) . The resulting function runs action(this(x)) where this is defined.
  • Definition Classes
    • PartialFunction
  • Since
    • 2.10
  • See also
    • applyOrElse .

(defined at scala.PartialFunction)

Concrete Value Members From scala.runtime.AbstractPartialFunction

def apply(x: T1): R

Apply the body of this function to the argument.

  • returns
    • the result of function application.
  • Definition Classes
    • AbstractPartialFunction → Function1

(defined at scala.runtime.AbstractPartialFunction)

Instance Constructors From scala.runtime.AbstractPartialFunction

new AbstractPartialFunction()

(defined at scala.runtime.AbstractPartialFunction)

Full Source:

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

package scala
package runtime

/** `AbstractPartialFunction` reformulates all operations of its supertrait `PartialFunction`
 *  in terms of `isDefinedAt` and `applyOrElse`.
 *
 *  This allows more efficient implementations in many cases:
 *  - optimized `orElse` method supports chained `orElse` in linear time,
 *    and with no slow-down if the `orElse` part is not needed.
 *  - optimized `lift` method helps to avoid double evaluation of pattern matchers & guards
 *    of partial function literals.
 *
 *  This trait is used as a basis for implementation of all partial function literals.
 *
 *  @author  Pavel Pavlov
 *  @since   2.10
 */
abstract class AbstractPartialFunction[@specialized(scala.Int, scala.Long, scala.Float, scala.Double) -T1, @specialized(scala.Unit, scala.Boolean, scala.Int, scala.Float, scala.Long, scala.Double) +R] extends Function1[T1, R] with PartialFunction[T1, R] { self =>
  // this method must be overridden for better performance,
  // for backwards compatibility, fall back to the one inherited from PartialFunction
  // this assumes the old-school partial functions override the apply method, though
  // override def applyOrElse[A1 <: T1, B1 >: R](x: A1, default: A1 => B1): B1 = ???

  // probably okay to make final since classes compiled before have overridden against the old version of AbstractPartialFunction
  // let's not make it final so as not to confuse anyone
  /*final*/ def apply(x: T1): R = applyOrElse(x, PartialFunction.empty)
}