scala.runtime.AbstractPartialFunction.scala Maven / Gradle / Ivy
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
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.
*/
abstract class AbstractPartialFunction[@specialized(Specializable.Arg) -T1, @specialized(Specializable.Return) +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)
}