org.scalactic.TraversableEqualityConstraints.scala Maven / Gradle / Ivy
/*
* 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.scalactic
/**
* Provides three implicit methods that loosen the equality constraint defined by TypeCheckedTripleEquals
* for Scala Traversables to one that more closely matches Scala's approach to Traversable equality.
*
*
* Scala's approach to Traversable equality is that if the objects being compared are ether both Seqs, both Sets,
* or both Maps, the elements are compared to determine equality.
* This means you could compare an immutable Vector and a mutable ListBuffer for equality, for instance, and get true so long as the
* two Seqs contained the same elements in the same order. Here's an example:
*
*
*
* scala> import scala.collection.mutable.ListBuffer
* import scala.collection.mutable.ListBuffer
*
* scala> Vector(1, 2) == ListBuffer(1, 2)
* res0: Boolean = true
*
*
*
* Such a comparison would not, however, compile if you used === under TypeCheckedTripleEquals,
* because Vector and ListBuffer are not in a subtype/supertype relationship:
*
*
*
* scala> import org.scalactic._
* import org.scalactic._
*
* scala> import TypeCheckedTripleEquals._
* import TypeCheckedTripleEquals._
*
* scala> Vector(1, 2) === ListBuffer(1, 2)
* <console>:16: error: types scala.collection.immutable.Vector[Int] and
* scala.collection.mutable.ListBuffer[Int] do not adhere to the equality constraint selected for
* the === and !== operators; the missing implicit parameter is of type
* org.scalactic.CanEqual[scala.collection.immutable.Vector[Int],
* scala.collection.mutable.ListBuffer[Int]]
* Vector(1, 2) === ListBuffer(1, 2)
* ^
*
*
*
* If you mix or import the implicit conversion provided by TraversableEqualityConstraint, however, the comparison will be allowed:
*
*
*
* scala> import TraversableEqualityConstraints._
* import TraversableEqualityConstraints._
*
* scala> Vector(1, 2) === ListBuffer(1, 2)
* res2: Boolean = true
*
*
*
* The equality constraints provided by this trait require that left and right sides are both subclasses of either scala.collection.GenSeq,
* scala.collection.GenSet, or scala.collection.GenMap, and that
* an CanEqual can be found for the element types for Seq and Set, or the key and value types for Maps. In
* the example above, both the Vector and
* ListBuffer are subclasses of scala.collection.GenSeq, and the regular TypeCheckedTripleEquals provides equality
* constraints for the element types, both of which are Int. By contrast, this
* trait would not allow a Vector[Int] to be compared against a ListBuffer[java.util.Date], because no equality constraint
* will exist between the element types Int and Date:
*
*
*
* scala> import java.util.Date
* import java.util.Date
*
* scala> Vector(1, 2) === ListBuffer(new Date, new Date)
* <console>:20: error: types scala.collection.immutable.Vector[Int] and
* scala.collection.mutable.ListBuffer[java.util.Date] do not adhere to the equality constraint selected for
* the === and !== operators; the missing implicit parameter is of type
* org.scalactic.CanEqual[scala.collection.immutable.Vector[Int],
* scala.collection.mutable.ListBuffer[java.util.Date]]
* Vector(1, 2) === ListBuffer(new Date, new Date)
* ^
*
*
*
* This trait simply mixes together SeqEqualityConstraints,
* SetEqualityConstraints,
* and MapEqualityConstraints.
*
*
* @author Bill Venners
*/
trait TraversableEqualityConstraints extends SeqEqualityConstraints with SetEqualityConstraints with MapEqualityConstraints
/**
* Companion object that facilitates the importing of TraversableEqualityConstraints members as
* an alternative to mixing it in. One use case is to import TraversableEqualityConstraints members so you can use
* them in the Scala interpreter.
*/
object TraversableEqualityConstraints extends TraversableEqualityConstraints