CharSet

Same reasoning as | above - SeqOps also inherits an intersect (multiset intersection by element equality, not numeric overlap).

cs.union(other) here would make the compiler's overload search also consider (and silently bind to instead of union above) the inherited, deprecated SeqOps.union - CharSet is transparently ArraySeq[Range] in this defining scope. Renaming the import forces resolution to this union specifically, since unionRenamed has nothing else to collide with. @nowarn on the whole method (rather than the import line itself, which doesn't accept annotations) silences the resulting - and, here, incorrect - "unused import" warning: the renamed import is used, just via extension-call syntax (cs.unionRenamed(...)) the unused-import checker doesn't recognize as a use.