----- Mail original ----- > De: "Brian Goetz" <brian.go...@oracle.com> > À: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "Guy Steele" <guy.ste...@oracle.com>, "John Rose" > <john.r.r...@oracle.com>, "amber-spec-experts" > <amber-spec-experts@openjdk.java.net> > Envoyé: Mercredi 12 Août 2020 22:05:02 > Objet: Re: Next up for patterns: type patterns in switch
> Since I am always the one saying "state your concern, not your > solution", let me frame this: > >> But i still think having a keyword to signal that a pattern (not a >> case) is total is better than letting people guess. > > From this I take away that (a) the rules we've proposed for totality vs > not are mostly OK in terms of their expressiveness and their defaults, > but (b) you are worried that it is too subtle for Java developers to > determine whether a given sub-tree of a pattern is total on the part it > is matching, so (c) you would like some additional assertions to say > "this is total, error if I'm wrong". These assertions benefit would both > the writer (to catch errors) and reader (so totality snaps off the page.) > > Do I have it right? yes, you can add (d) the keyword also makes the fact that a pattern is total a local property so actions at distance that change the pattern from total to non total will lead to an error. > > But isn't the "switch is total" kind of the half-brother of this story, > too? Since statement switches might be total or partial, stating the > intent would be useful in the same way, right? (To be clear, I think > this is two separate issues, but they are related.) yes, there is no problem with the expression switches and statement switch with one total pattern at top-level (if there is a keyword for pattern totality), but if a statement switch is exhaustive it can become partial after a change and there is currently no way to express that you want to keep the statement switch total. Rémi
