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ScalaUtils is an open-source library for Scala projects that contains portions of the ScalaTest project that may make sense to use in production.
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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.scalautils

/**
 * Class used via an implicit conversion to enable two objects to be compared with
 * === and !== with a Boolean result and an enforced type constraint between
 * two object types. For example:
 *
 *  * assert(a === b)
 * assert(c !== d)
 * 
 *
 * 
 * You can also check numeric values against another with a tolerance. Here are some examples:
 * 
 *
 *  * assert(a === (2.0 +- 0.1))
 * assert(c !== (2.0 +- 0.1))
 * 
 *
 * @param left An object to convert to Equalizer, which represents the value
 *     on the left side of a === or !== invocation.
 *
 * @author Bill Venners
 */
class CheckingEqualizer[L](left: L) {

  /**
   * Compare two objects for equality, returning a Boolean, using the EqualityConstraint instance passed as constraint.
   *
   * @param right the object to compare for equality with left, passed to the constructor
   * @param constraint an implicit EqualityConstraint instance that enforces a relationship between types L and R and
   *    defines a way of calculating equality for objects of type L
   * @return true if the left and right objects are equal according to the passed EqualityConstraint instance.
   */
  def ===[R](right: R)(implicit constraint: EqualityConstraint[L, R]): Boolean = constraint.areEqual(left, right)

  /**
   * Compare two objects for inequality, returning a Boolean, using the EqualityConstraint instance passed as constraint.
   *
   * @param right the object to compare for inequality with left, passed to the constructor
   * @param constraint an implicit EqualityConstraint instance that enforces a relationship between types L and R and
   *    defines a way of calculating equality for objects of type L
   * @return true if the left and right objects are not equal according to the passed EqualityConstraint instance.
   */
  def !==[R](right: R)(implicit constraint: EqualityConstraint[L, R]): Boolean = !constraint.areEqual(left, right)

  /**
   * Determine whether a numeric object is within the passed Interval, returning a Boolean.
   *
   * @param interval the Interval against which to compare the value passed to the constructor as left 
   * @return true if the value passed to the constructor as left is not within the Interval passed to this method.
   */
  def ===(interval: Interval[L]): Boolean = if (interval != null) interval.isWithin(left) else left == interval

  /**
   * Determine whether a numeric object is outside the passed Interval, returning a Boolean.
   *
   * @param interval the Interval against which to compare the value passed to the constructor as left 
   * @return true if the value passed to the constructor as left is not within the Interval passed to this method.
   */
  def !==(interval: Interval[L]): Boolean = if (interval != null) !interval.isWithin(left) else left != interval
}