Scala example source code file (Equiv.scala)

This example Scala source code file (Equiv.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

any, anyref, boolean, comparator, equiv, lowpriorityequiv, s, serializable, t

The Equiv.scala Scala example source code

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

package scala
package math

import java.util.Comparator

/** A trait for representing equivalence relations.  It is important to
 *  distinguish between a type that can be compared for equality or
 *  equivalence and a representation of equivalence on some type. This
 *  trait is for representing the latter.
 *
 *  An [[http://en.wikipedia.org/wiki/Equivalence_relation equivalence relation]]
 *  is a binary relation on a type. This relation is exposed as
 *  the `equiv` method of the `Equiv` trait.  The relation must be:
 *
 *    1. reflexive: `equiv(x, x) == true` for any x of type `T`.
 *    1. symmetric: `equiv(x, y) == equiv(y, x)` for any `x` and `y` of type `T`.
 *    1. transitive: if `equiv(x, y) == true` and `equiv(y, z) == true`, then
 *       `equiv(x, z) == true` for any `x`, `y`, and `z` of type `T`.
 *
 *  @author  Geoffrey Washburn, Paul Phillips
 *  @version 1.0, 2008-04-03
 *  @since 2.7
 */

trait Equiv[T] extends Any with Serializable {
  /** Returns `true` iff `x` is equivalent to `y`.
   */
  def equiv(x: T, y: T): Boolean
}

trait LowPriorityEquiv {
  self: Equiv.type =>

  implicit def universalEquiv[T] : Equiv[T] = universal[T]
}

object Equiv extends LowPriorityEquiv {
  def reference[T <: AnyRef] : Equiv[T] = new Equiv[T] {
    def equiv(x: T, y: T) = x eq y
  }
  def universal[T] : Equiv[T] = new Equiv[T] {
    def equiv(x: T, y: T) = x == y
  }
  def fromComparator[T](cmp: Comparator[T]): Equiv[T] = new Equiv[T] {
    def equiv(x: T, y: T) = cmp.compare(x, y) == 0
  }
  def fromFunction[T](cmp: (T, T) => Boolean): Equiv[T] = new Equiv[T] {
    def equiv(x: T, y: T) = cmp(x, y)
  }
  def by[T, S: Equiv](f: T => S): Equiv[T] =
    fromFunction((x, y) => implicitly[Equiv[S]].equiv(f(x), f(y)))

  def apply[T: Equiv] : Equiv[T] = implicitly[Equiv[T]]
}