MapEqualityConstraints
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object MapEqualityConstraints
| package scalactic
Provides an equality constraint that allows two subtypes of scala.collection.GenMaps to be compared for equality with === so long
as an EqualityConstraint is available for both key types and both value types.
Provides an equality constraint that allows two subtypes of scala.collection.GenMaps to be compared for equality with === so long
as an EqualityConstraint is available for both key types and both value types.
Provides an implicit method that loosens the equality constraint defined by
TypeCheckedTripleEqualsorConversionCheckedTripleEqualsfor ScalaMaps to one that more closely matches Scala's approach toMapequality.Scala's approach to
Mapequality is that if both objects being compared areMaps, the elements are compared to determine equality. This means you could compare an immutableTreeMapand a mutableHashMapfor equality, for instance, and get true so long as the two maps contained the same key-value mappings. Here's an example:scala> import scala.collection.immutable.TreeMap import scala.collection.immutable.TreeMap scala> import scala.collection.mutable.HashMap import scala.collection.mutable.HashMap scala> TreeMap("one" -> 1, "two" -> 2) == HashMap("one" -> 1, "two" -> 2) res0: Boolean = trueSuch a comparison would not, however, compile if you used
===under eitherTypeCheckedTripleEqualsorConversionCheckedTripleEquals, becauseTreeMapandHashMapare 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> TreeMap("one" -> 1, "two" -> 2) === HashMap("one" -> 1, "two" -> 2) <console>:16: error: types scala.collection.immutable.TreeMap[String,Int] and scala.collection.mutable.HashMap[String,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.TreeMap[String,Int], scala.collection.mutable.HashMap[String,Int]] TreeMap("one" -> 1, "two" -> 2) === HashMap("one" -> 1, "two" -> 2) ^If you mix or import the implicit conversion provided by
MapEqualityConstraint, however, the comparison will be allowed:scala> import MapEqualityConstraints._ import MapEqualityConstraints._ scala> TreeMap("one" -> 1, "two" -> 2) === HashMap("one" -> 1, "two" -> 2) res2: Boolean = trueThe equality constraint provided by this trait requires that both left and right sides are subclasses of
scala.collection.GenMapand that anEqualityConstraintcan be found for both key types and both value types. In the example above, both theTreeMapandHashMapare subclasses ofscala.collection.GenMap, and the regularTypeCheckedTripleEqualsprovides equality constraints for the key types, both of which areString, and value types, both of which areInt. By contrast, this trait would not allow aTreeMap[String, Int]to be compared against aHashMap[String, java.util.Date], because no equality constraint will exist between the value typesIntandDate:scala> import java.util.Date import java.util.Date scala> TreeMap("one" -> 1, "two" -> 2) === HashMap("one" -> new Date, "two" -> new Date) <console>:20: error: types scala.collection.immutable.TreeMap[String,Int] and scala.collection.mutable.HashMap[String,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.TreeMap[String,Int], scala.collection.mutable.HashMap[String,java.util.Date]] TreeMap("one" -> 1, "two" -> 2) === HashMap("one" -> new Date, "two" -> new Date) ^