Please before submitting a wishlist, please take a look at this video that explain what can be the cost of a change (even if in this case, it's a really small change it's only a VM change) [ https://www.youtube.com/watch?v=-k_IicifbxQ | https://www.youtube.com/watch?v=-k_IicifbxQ ]
regards, Rémi > De: "Brian Goetz" <brian.go...@oracle.com> > À: "amber-spec-experts" <amber-spec-experts@openjdk.java.net> > Envoyé: Mardi 21 Août 2018 13:57:51 > Objet: Fwd: Small things Java lets you do, but not everywhere. > Received via the spec-comments list. Not a comment on any specific extant > project; instead, a wish-list, and mostly stuff we’ve seen before — array > literals, generic maps, union types. >> Begin forwarded message: >> From: Jeremy Barrow < [ mailto:jeremy.a.bar...@gmail.com | >> jeremy.a.bar...@gmail.com ] > >> Subject: Small things Java lets you do, but not everywhere. >> Date: August 13, 2018 at 6:59:33 AM EDT >> To: [ mailto:amber-spec-comme...@openjdk.java.net | >> amber-spec-comme...@openjdk.java.net ] >> Heyo, I just wanted to send off a quick email about some of the things that >> I think would be easy pickings for Amber to tackle. >> More specifically, they're things in the language that are either not >> completely fleshed out due to lack of interest, or, more likely, for some >> technical reason. >> The first one is definitely array literals: >> I've been using Java for 7ish years at this point, and honestly, I don't >> even know if I'm gonna get this right. >> The only place I'm aware of array literals being valid is for a field write. >> Not many people use arrays, as Lists are just better, but _very_ >> occasionally you do have to reach for an array. >> It would be nice if we could expand the array literal use case. >> Just about everywhere an expression could be expected, I think an array >> literal could be valid. >> I can image `return` statements working really well with it, and with the >> new expression switch, the break with value. >> I'll be honest, this is where the "easy pickings" part is no longer true. >> Class local generics (Field local generics?): >> I definitely think I'm not the only one who has written some static field >> that has a map which maps some arbitrary data container to some value, with >> the data container containing some type parameter that tells you what the >> value type is. >> `private static final Map<Key<?>, ?> data = ...` >> It would be a massive boon, if we could write that as something like: >> `private static final <T> Map<Key<T>, T> data = ...` >> Otherwise we have to cast everything we pull out of the map. >> I know it's of the correct type, but the compiler doesn't. >> This leads to some annoying stuff where generics aren't actually helping >> you, which is a bit counter intuitive. >> We have generics for methods, theoretically, it should be possible for >> fields. >> Union types: >> Now, I'll preface this with this might be difficult to translate into the >> VM right now, so erasure might be the only option for now (With type >> signatures being a possible route in the future). >> In a nutshell, declaring fields with union types. >> Right now, I either have to declare three different fields, making my >> memory usage suffer if I have tons of these objects (Which I normally do, >> because this specific class is a Token class for a lexer, and I parse >> massive input sources), also making it more error prone due to having three >> different ways to access the same data. >> Granted union types won't solve the last problem, but it doesn't help it. >> Technically, Java does have union types in catch signatures. >> Obviously, the catch signatures kinda get "collapsed", so it's not really >> the same, as there's a lot more needed under the hood here. >> Possibly. >> I think a quick prototype might be just to treat it as though I had written >> something like, and just erase it to Object: >> `private final <T extends String | Integer | Double> T data;` >> Obviously, we don't have union generics, so that would obviously have to be >> added, and honestly, I think that might be the can of worms I didn't plan >> on. >> So, I'll wrap it up there. >> Obviously, the generics and union types are quite.. large in scope, and >> aren't really easy, but I do think the array literals are something that >> could be touched on. >> Cheers, >> Jeremy.
