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Scala example source code file (PartialOrdering.scala)

This example Scala source code file (PartialOrdering.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Scala tags/keywords

boolean, boolean, equiv, equiv, option, partialordering, partialordering, t, t

The Scala PartialOrdering.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */



package scala.math

/** <p>
 *    A trait for representing partial orderings.  It is important to
 *    distinguish between a type that has a partial order and a representation 
 *    of partial ordering on some type.  This trait is for representing the
 *    latter.  
 *  </p>
 *  <p>
 *    A <a href="http://en.wikipedia.org/wiki/Partial_order">partial ordering 
 *    is a binary relation on a type <code>T that is also an equivalence 
 *    relation on values of type <code>T.  This relation is exposed as
 *    the <code>lteq method of the PartialOrdering trait.  
 *    This relation must be:
 *  </p>
 *  <ul>
 *    <li>reflexive: lteq(x, x) == true, for any x of 
 *      type <code>T.
 *    <li>anti-symmetric: lteq(x, y) == true and
 *      <code>lteq(y, x) == true then equiv(x, y), for any
 *      <code>x and y of type T.
 *    <li>transitive: if lteq(x, y) == true and
 *      <code>lteq(y, z) == true then lteq(x, z) == true,
 *      for any <code>x, y, and z of type
 *      <code>T.
 * </ul>
 *
 *  @author  Geoffrey Washburn
 *  @version 1.0, 2008-04-0-3
 *  @since 2.7
 */

trait PartialOrdering[T] extends Equiv[T] {
  outer =>
  
  /** Result of comparing <code>x with operand y.
   *  Returns <code>None if operands are not comparable.
   *  If operands are comparable, returns <code>Some(r) where
   *  <code>r < 0    iff    x < y
   *  <code>r == 0   iff    x == y
   *  <code>r > 0    iff    x > y
   */
  def tryCompare(x: T, y: T): Option[Int]
  
  /** Returns <code>true iff x comes before 
   *  <code>y in the ordering.
   */
  def lteq(x: T, y: T): Boolean

  /** Returns <code>true iff y comes before
   *  <code>x in the ordering. 
   */
  def gteq(x: T, y: T): Boolean = lteq(y, x)

  /** Returns <code>true iff x comes before 
   *  <code>y in the ordering and is not the same as y.
   */
  def lt(x: T, y: T): Boolean = lteq(x, y) && !equiv(x, y)

  /** Returns <code>true iff y comes before 
   *  <code>x in the ordering and is not the same as x.
   */
  def gt(x: T, y: T): Boolean = gteq(x, y) && !equiv(x, y)

  /** Returns <code>true iff x is equivalent to
   *  <code>y in the ordering. 
   */
  def equiv(x: T, y: T): Boolean = lteq(x,y) && lteq(y,x)

  def reverse : PartialOrdering[T] = new PartialOrdering[T] {
    override def reverse = outer
    def lteq(x: T, y: T) = outer.lteq(y, x)
    def tryCompare(x: T, y: T) = outer.tryCompare(y, x)
  }
}

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