----- Mail original ----- > De: "Brian Goetz" <brian.go...@oracle.com> > À: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "valhalla-spec-experts" <valhalla-spec-experts@openjdk.java.net> > Envoyé: Mercredi 1 Mai 2019 15:03:42 > Objet: Re: Is V? what we need ?
>> we need V? >> - to represent the L variation of a Q type. >> - to interact with generics that are not reified. > > These are the proximate causes, but I think this undersells it. > >> V? does that but does far more, V? is a super type of V which is dangerous, >> because people will use it as parameter of function instead of V because >> it's a >> super type and works with null. >> Here we are back to a world were every value types may be null. > > Whoa, I think you just skipped a few dozen steps … use the most super type possible for a parameter is the usual rule hence "program to an interface", i don't think i'v skipped a lot of steps. > > Perhaps you could clarify this with some examples of “I worry people will > write > __ instead of ___, and then __ will happen.” i worry people will code as we have told them to code. > >> I believe that the issue is that V? should work as a box and currently V? is >> to >> powerful/useful as a box so people will start to use it as a true type. > > Again, lots to unpack here: > > - What, in your mind, is the difference between a box and an adjunction? not sure to fully understand the question, is it about the syntax ? > - What benefits do box types give here? a box is a necessary evil, everybody want to write an ArrayList<int> but we are not there yet, so we provide just the right abstraction to deal with value type in generics, not more. > - What risks do you envision from “using V? as a true type”? V? everywhere where V should be used, or worst, people using V? half of the time, randomly. Rémi
