SeqEqualityConstraints
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object SeqEqualityConstraints
| package scalactic
Provides an equality constraint that allows two subtypes of scala.collection.GenSeqs to be compared for equality with === so long
as an EqualityConstraint is available for the element types.
Provides an equality constraint that allows two subtypes of scala.collection.GenSeqs to be compared for equality with === so long
as an EqualityConstraint is available for the element types.
Provides an implicit method that loosens the equality constraint defined by
TypeCheckedTripleEqualsorConversionCheckedTripleEqualsfor ScalaSeqs to one that more closely matches Scala's approach toSeqequality.Scala's approach to
Seqequality is that if both objects being compared areSeqs, the elements are compared to determine equality. This means you could compare an immutableVectorand a mutableListBufferfor equality, for instance, and get true so long as the twoSeqs contained the same elements in the same order. Here's an example:Such a comparison would not, however, compile if you used
===under eitherTypeCheckedTripleEqualsorConversionCheckedTripleEquals, becauseVectorandListBufferare not in a subtype/supertype relationship, nor does an implicit conversion by default exist between them: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.EqualityConstraint[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
SeqEqualityConstraint, however, the comparison will be allowed:The equality constraint provided by this trait requires that both left and right sides are subclasses of
scala.collection.GenSeqand that anEqualityConstraintcan be found for the element types. In the example above, both theVectorandListBufferare subclasses ofscala.collection.GenSeq, and the regularTypeCheckedTripleEqualsprovides equality constraints for the element types, both of which areInt. By contrast, this trait would not allow aVector[Int]to be compared against aListBuffer[java.util.Date], because no equality constraint will exist between the element typesIntandDate: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.EqualityConstraint[scala.collection.immutable.Vector[Int], scala.collection.mutable.ListBuffer[java.util.Date]] Vector(1, 2) === ListBuffer(new Date, new Date) ^