Annoying type signatures for .sets, .maps etc.

[sageserpent-open]

As of 1.12.0, Trials has the following methods for building trials of sets and maps:

  def sets: Trials[Set[_ <: Case]]

  def sortedSets(implicit
      ordering: Ordering[_ >: Case]
  ): Trials[SortedSet[_ <: Case]]

  def maps[Value](values: Trials[Value]): Trials[Map[_ <: Case, Value]]

  def sortedMaps[Value](values: Trials[Value])(implicit
      ordering: Ordering[_ >: Case]
  ): Trials[SortedMap[_ <: Case, Value]]

I can't remember now just why the wildcard types were thought necessary, other than that this may have been forced due to the odd lack of covariance in the Scala Set and Map classes - or was it to work with the Java API?

Whatever the reason - it is annoying having to workaround the wildcard types, either by propagating them around test code, or doing .asInstanceOf to cast to the real type.

Worth a spike to see what the problem was and if it can be sorted out...

[sageserpent-open]

Spike tried - have cutover Trials.sets/sortedSets/maps/sortedMaps in the Scala API.

Tests pass, and tried a client project against a snapshot version of Americium ...

Works nicely, generating the correct test cases.

Delivering this as-is for the next release, 1.13.0 .

[sageserpent-open]

The new API looks like this:

  def sets[CovarianceFudge >: Case]: Trials[Set[CovarianceFudge]]

  def sortedSets[CovarianceFudge >: Case](implicit
      ordering: Ordering[CovarianceFudge]
  ): Trials[SortedSet[CovarianceFudge]]

  def maps[CovarianceFudge >: Case, Value](values: Trials[Value]): Trials[Map[CovarianceFudge, Value]]

  def sortedMaps[CovarianceFudge >: Case, Value](values: Trials[Value])(implicit
      ordering: Ordering[CovarianceFudge]
  ): Trials[SortedMap[CovarianceFudge, Value]]

The idea is not to specify the type parameter CovarianceFudge - it will be inferred to be Case, which is what the client code wants, but having the type bound CovarianceFudge >: Case sidesteps the problem that was being worked around in the past - namely that Set and Map are invariant in the key type parameter, but Trials is covariant in its Case type parameter.

This has gone out in release 1.13.0, Git commit SHA 1ffdf8c.

[sageserpent-open]

There is a similar problem in getting the Java form of the API from a Scala Trials via Trials.javaApi. May as well fix that under this ticket as well...

[sageserpent-open]

The fix went out in release 1.13.1, Git commit SHA 24ac99e.