Scala example source code file (Function.scala)

This example Scala source code file (Function.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

function, partialfunction, r, seq, t, tuple2, tuple3, tuple4, tuple5, u

The Function.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */



package scala

/** A module defining utility methods for higher-order functional programming.
 *
 *  @author  Martin Odersky
 *  @version 1.0, 29/11/2006
 */
object Function {
  /** Given a sequence of functions `f,,1,,`, ..., `f,,n,,`, return the
   *  function `f,,1,, andThen ... andThen f,,n,,`.
   *
   *  @param fs The given sequence of functions
   */
  def chain[a](fs: Seq[a => a]): a => a = { x => (x /: fs) ((x, f) => f(x)) }

  /** The constant function */
  def const[T, U](x: T)(y: U): T = x

  /** Turns a function `A => Option[B]` into a `PartialFunction[A, B]`.
   *
   *  '''Important note''': this transformation implies the original function
   *  may be called 2 or more times on each logical invocation, because the
   *  only way to supply an implementation of `isDefinedAt` is to call the
   *  function and examine the return value.
   *  See also [[scala.PartialFunction]], method `applyOrElse`.
   *
   *  @param   f    a function `T => Option[R]`
   *  @return       a partial function defined for those inputs where
   *                f returns `Some(_)` and undefined where `f` returns `None`.
   *  @see [[scala.PartialFunction]], method `lift`.
   */
  def unlift[T, R](f: T => Option[R]): PartialFunction[T, R] = PartialFunction.unlifted(f)

  /** Uncurrying for functions of arity 2. This transforms a unary function
   *  returning another unary function into a function of arity 2.
   */
  def uncurried[a1, a2, b](f: a1 => a2 => b): (a1, a2) => b = {
    (x1, x2) => f(x1)(x2)
  }

  /** Uncurrying for functions of arity 3.
   */
  def uncurried[a1, a2, a3, b](f: a1 => a2 => a3 => b): (a1, a2, a3) => b = {
    (x1, x2, x3) => f(x1)(x2)(x3)
  }

  /** Uncurrying for functions of arity 4.
   */
  def uncurried[a1, a2, a3, a4, b](f: a1 => a2 => a3 => a4 => b): (a1, a2, a3, a4) => b = {
    (x1, x2, x3, x4) => f(x1)(x2)(x3)(x4)
  }

  /** Uncurrying for functions of arity 5.
   */
  def uncurried[a1, a2, a3, a4, a5, b](f: a1 => a2 => a3 => a4 => a5 => b): (a1, a2, a3, a4, a5) => b  =  {
    (x1, x2, x3, x4, x5) => f(x1)(x2)(x3)(x4)(x5)
  }

  /** Tupling for functions of arity 2. This transforms a function
   *  of arity 2 into a unary function that takes a pair of arguments.
   *
   *  @note  These functions are slotted for deprecation, but it is on
   *  hold pending superior type inference for tupling anonymous functions.
   */
  // @deprecated("Use `f.tupled` instead")
  def tupled[a1, a2, b](f: (a1, a2) => b): Tuple2[a1, a2] => b = {
    case Tuple2(x1, x2) => f(x1, x2)
  }

  /** Tupling for functions of arity 3. This transforms a function
   *  of arity 3 into a unary function that takes a triple of arguments.
   */
  // @deprecated("Use `f.tupled` instead")
  def tupled[a1, a2, a3, b](f: (a1, a2, a3) => b): Tuple3[a1, a2, a3] => b = {
    case Tuple3(x1, x2, x3) => f(x1, x2, x3)
  }

  /** Tupling for functions of arity 4. This transforms a function
   *  of arity 4 into a unary function that takes a 4-tuple of arguments.
   */
  // @deprecated("Use `f.tupled` instead")
  def tupled[a1, a2, a3, a4, b](f: (a1, a2, a3, a4) => b): Tuple4[a1, a2, a3, a4] => b = {
    case Tuple4(x1, x2, x3, x4) => f(x1, x2, x3, x4)
  }

  /** Tupling for functions of arity 5. This transforms a function
   *  of arity 5 into a unary function that takes a 5-tuple of arguments.
   */
  // @deprecated("Use `f.tupled` instead")
  def tupled[a1, a2, a3, a4, a5, b](f: (a1, a2, a3, a4, a5) => b): Tuple5[a1, a2, a3, a4, a5] => b = {
    case Tuple5(x1, x2, x3, x4, x5) => f(x1, x2, x3, x4, x5)
  }

  /** Un-tupling for functions of arity 2. This transforms a function taking
   *  a pair of arguments into a binary function which takes each argument separately.
   */
  def untupled[a1, a2, b](f: Tuple2[a1, a2] => b): (a1, a2) => b = {
    (x1, x2) => f(Tuple2(x1, x2))
  }

  /** Un-tupling for functions of arity 3. This transforms a function taking
   *  a triple of arguments into a ternary function which takes each argument separately.
   */
  def untupled[a1, a2, a3, b](f: Tuple3[a1, a2, a3] => b): (a1, a2, a3) => b = {
    (x1, x2, x3) => f(Tuple3(x1, x2, x3))
  }

  /** Un-tupling for functions of arity 4. This transforms a function taking
   *  a 4-tuple of arguments into a function of arity 4 which takes each argument separately.
   */
  def untupled[a1, a2, a3, a4, b](f: Tuple4[a1, a2, a3, a4] => b): (a1, a2, a3, a4) => b = {
    (x1, x2, x3, x4) => f(Tuple4(x1, x2, x3, x4))
  }

  /** Un-tupling for functions of arity 5. This transforms a function taking
   *  a 5-tuple of arguments into a function of arity 5 which takes each argument separately.
   */
  def untupled[a1, a2, a3, a4, a5, b](f: Tuple5[a1, a2, a3, a4, a5] => b): (a1, a2, a3, a4, a5) => b = {
    (x1, x2, x3, x4, x5) => f(Tuple5(x1, x2, x3, x4, x5))
  }
}