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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 any two objects to be compared with
 * === and !== with a Boolean result and no 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 Equalizer[L](left: L) {

  /**
   * Compare two objects for equality, returning a Boolean, using the Equality type class passed as equality.
   *
   * @param right the object to compare for equality with left, passed to the constructor
   * @param equality an implicit Equality type class that 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 Equality type class.
   */
  def ===(right: Any)(implicit equality: Equality[L]): Boolean = equality.areEqual(left, right)

  /**
   * Compare two objects for inequality, returning a Boolean, using the Equality type class passed as equality.
   *
   * @param right the object to compare for inequality with left, passed to the constructor
   * @param equality an implicit Equality type class that 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 Equality type class.
   */
  def !==(right: Any)(implicit equality: Equality[L]): Boolean = !equality.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 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

  /**
   * Determine whether an object reference is null.
   *
   * @param literalNull a null value against which to compare the value passed to the constructor as left for equality
   * @return true if the value passed to the constructor as left is null.
   */
  def ===(literalNull: Null): Boolean = left == null

  /**
   * Determines whether an object reference is non-null.
   *
   * @param literalNull a null value against which to compare the value passed to the constructor as left for inequality
   * @return true if the value passed to the constructor as left is non-null.
   */
  def !==(literalNull: Null): Boolean = left != null
}