Set is invariant in its type parameter because of the concept behind sets as functions. The following signatures should clarify things slightly: trait Set[A] extends (A=>Boolean) { def apply(e: A): Boolean } If Set were covariant in A, the apply method would be unable to take a parameter of type A due to the contravariance … Read more
I hope it’s not a “suicide note”, but I can see your point. You hit on what is at the same time both a strength and a problem of Scala: its extensibility. This lets us implement most major functionality in libraries. In some other languages, sequences with something like map or collect would be built … Read more
The answer is found on the definition of map: def map[B, That](f : (A) => B)(implicit bf : CanBuildFrom[Repr, B, That]) : That Note that it has two parameters. The first is your function and the second is an implicit. If you do not provide that implicit, Scala will choose the most specific one available. … Read more
You can’t do that. SortedMap sorts by keys, not values. If you want it sorted by value, you gotta use ListMap, and can’t avoid converting to List: ListMap(i.toList.sortBy(-_._2):_*) There isn’t really too much wrong with converting to list, since you are loading the whole thing in memory anyway. This is faster too, than building a … Read more