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/*
 * Copyright 2001-2013 Artima, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.scalatest.matchers

import org.scalactic.Prettifier

/**
 * Singleton object that provides unapply method to extract failure message from MatchResult
 * having matches property value of false.
 *
 * @author Bill Venners
 * @author Chee Seng
 */
object MatchFailed {
  /**
   * Extractor enabling patterns that match MatchResult having matches property value of false,
   * extracting the contained failure message.
   *
   * 
   * For example, you can use this extractor to get the failure message of a MatchResult like this:
   * 
   *
   *    * matchResult match {
   *   case MatchFailed(failureMessage) => // do something with failureMessage
   *   case _ => // when matchResult.matches equal to true
   * }
   * 
   *
   * @param matchResult the MatchResult to extract the failure message from.
   * @return a Some wrapping the contained failure message if matchResult.matches is equal to true, else None.
   */
  def unapply(matchResult: MatchResult)(implicit prettifier: Prettifier): Option[String] = {
    if (!matchResult.matches) Some(matchResult.failureMessage(prettifier)) else None
  }
}