I think i prefer break-with, the problem of break-return is that people will write it break return without the hyphen, break return is in my opinion too close to return if you read the code too fast and a break return without a value means nothing unlike a regular return.
I like break-with because it's obvious that you have to say with what value you want to break, which is exactly the issue we have with the current break syntax. So i vote for break-with instead of break, as Brian said, the expression switch is currently a preview feature of 12 so we can still tweak the syntax a bit. Rémi ----- Mail original ----- > De: "Guy Steele" <guy.ste...@oracle.com> > À: "Brian Goetz" <brian.go...@oracle.com> > Cc: "amber-spec-experts" <amber-spec-experts@openjdk.java.net> > Envoyé: Mardi 8 Janvier 2019 18:23:36 > Objet: Re: We need more keywords, captain! > Actually, even better than `break-with` would be `break-return`. It’s > clearly a > kind of `break`, and also clearly a kind of `return`. > > I think maybe this application alone has won me over to the idea of hyphenated > keywords. > > (Then again, for this specific application we don’t even need the hyphen; we > could just write `break return v;`.) > > —Guy > >> On Jan 8, 2019, at 12:35 PM, Brian Goetz <brian.go...@oracle.com> wrote: >> >> When discussing this today at our compiler meeting, we realized a few more >> places where the lack of keywords produce distortions we don't even notice. >> In >> expression switch, we settled on `break value` as the way to provide a value >> for a switch expression when the shorthand (`case L -> e`) doesn't suffice, >> but >> this was painful for everyone. It's painful for users because there's now >> work >> required to disambiguate whether `break foo` is a labeled break or a value >> break; it was even more painful to specify, because a new form of abrupt >> completion had to be threaded through the spec. >> >> Being able to call this something like `break-with v` (or some other derived >> keyword) would have made this all a lot simpler. (BTW, we can still do this, >> since expression-switch is still in preview.) >> >> Moral of the story: even just a few minutes of brainstorming led us to >> several >> applications of this approach that we hadn't seen a few days ago. >> >> On 1/8/2019 10:22 AM, Brian Goetz wrote: >>> This document proposes a possible move that will buy us some breathing room >>> in >>> the perpetual problem where the keyword-management tail wags the >>> programming-model dog. >>> >>> >>> ## We need more keywords, captain! >>> >>> Java has a fixed set of _keywords_ (JLS 3.9) which are not allowed to >>> be used as identifiers. This set has remained quite stable over the >>> years (for good reason), with the exceptions of `assert` added in 1.4, >>> `enum` added in 5, and `_` added in 9. In addition, there are also >>> several _reserved identifiers_ (`true`, `false`, and `null`) which >>> behave almost like keywords. >>> >>> Over time, as the language evolves, language designers face a >>> challenge; the set of keywords imagined in version 1.0 are rarely >>> suitable for expressing all the things we might ever want our language >>> to express. We have several tools at our disposal for addressing this >>> problem: >>> >>> - Eminent domain. Take words that were previously identifiers, and >>> turn them into keywords, as we did with `assert` in 1.4. >>> >>> - Recycle. Repurpose an existing keyword for something that it was >>> never really meant for (such as using `default` for annotation >>> values or default methods). >>> >>> - Do without. Find a way to pick a syntax that doesn't require a >>> new keyword, such as using `@interface` for annotations instead of >>> `annotation` -- or don't do the feature at all. >>> >>> - Smoke and mirrors. Create the illusion of context-dependent >>> keywords through various linguistic heroics (restricted keywords, >>> reserved type names.) >>> >>> In any given situation, all of these options are on the table -- but >>> most of the time, none of these options are very good. The lack of >>> reasonable options for extending the syntax of the language threatens >>> to become a significant impediment to language evolution. >>> >>> #### Why not "just" make new keywords? >>> >>> While it may be legal for us to declare `i` to be a keyword in a >>> future version of Java, this would likely break every program in the >>> world, since `i` is used so commonly as an identifier. (When the >>> `assert` keyword was added in 1.4, it broke every testing framework.) >>> The cost of remediating the effect of such incompatible changes varies >>> as well; invalidating a name choice for a local variable has a local >>> fix, but invalidating the name of a public type or an interface >>> method might well be fatal. >>> >>> Additionally, the keywords we're likely to want to reclaim are often >>> those that are popular as identifiers (e.g., `value`, `var`, >>> `method`), making such fatal collisions more likely. In some cases, >>> if the keyword candidate in question is sufficiently rarely used as an >>> identifier, we might still opt to take that source-compatibility hit >>> -- but names that are less likely to collide (e.g., >>> `usually_but_not_always_final`) are likely not the ones we want in our >>> language. Realistically, this is unlikely to be a well we can go to >>> very often, and the bar must be very high. >>> >>> #### Why not "just" live with the keywords we have? >>> >>> Reusing keywords in multiple contexts has ample precedent in >>> programming languages, including Java. (For example, we (ab)use `final` >>> for "not mutable", "not overridable", and "not extensible".) >>> Sometimes, using an existing keyword in a new context is natural and >>> sensible, but usually it's not our first choice. Over time, as the >>> range of demands we place on our keyword set expands, this may well >>> descend into the ridiculous; no one wants to use `null final` as a way >>> of negating finality. (While one might think such things are too >>> ridiculous to consider, note that we received serious-seeming >>> suggestions during JEP 325 to use `new switch` to describe a switch >>> with different semantics. Presumably to be followed by `new new >>> switch` in ten years.) >>> >>> Of course, one way to live without making new keywords is to stop >>> evolving the language entirely. While there are some who think this >>> is a fine idea, doing so because of the lack of available tokens would >>> be a silly reason. We are convinced that Java has a long life ahead of >>> it, and developers are excited about new features that enable to them >>> to write more expressive and reliable code. >>> >>> #### Why not "just" make contextual keywords? >>> >>> At first glance, contextual keywords (and their friends, such as >>> reserved type identifiers) may appear to be a magic wand; they let us >>> create the illusion of adding new keywords without breaking existing >>> programs. But the positive track record of contextual keywords hides >>> a great deal of complexity and distortion. >>> >>> Each grammar position is its own story; contextual keywords that might >>> be used as modifiers (e.g., `readonly`) have different ambiguity >>> considerations than those that might be use in code (e.g., a `matches` >>> expression). The process of selecting a contextual keyword is not a >>> simple matter of adding it to the grammar; each one requires an >>> analysis of potential current and future interactions. Similarly, >>> each token we try to repurpose may have its own special >>> considerations; for example, we could justify the use of `var` as a >>> reserved type name because because the naming conventions are so >>> broadly adhered to. Finally, the use of contextual keywords in >>> certain syntactic positions can create additional considerations for >>> extending the syntax later. >>> >>> Contextual keywords create complexity for specifications, compilers, >>> and IDEs. With one or two special cases, we can often deal well >>> enough, but if special cases were to become more pervasive, this would >>> likely result in more significant maintenance costs or bug tail. While >>> it is easy to dismiss this as “not my problem”, in reality, this is >>> everybody’s problem. IDEs often have to guess whether a use of a >>> contextual keyword is a keyword or identifier, and it may not have >>> enough information to make a good guess until it’s seen more input. >>> This results in worse user highlighting, auto-completion, and >>> refactoring abilities — or worse. These problems quickly become >>> everyone's problems. >>> >>> So, while contextual keywords are one of the tools in our toolbox, >>> they should also be used sparingly. >>> >>> #### Why is this a problem? >>> >>> Aside from the obvious consequences of these problems (clunky syntax, >>> complexity, bugs), there is a more insidious hidden cost -- >>> distortion. The accidental details of keyword management pose a >>> constant risk of distortion in language design. >>> >>> One could consider the choice to use `@interface` instead of >>> `annotation` for annotations to be a distortion; having a descriptive >>> name rather than a funky combination of punctuation and keyword would >>> surely have made it easier for people to become familiar with >>> annotations. >>> >>> In another example, the set of modifiers (`public`, `private`, >>> `static`, `final`, etc) is not complete; there is no way to say “not >>> final” or “not static”. This, in turn, means that we cannot create >>> features where variables or classes are `final` by default, or members >>> are `static` by default, because there’s no way to denote the desire >>> to opt out of it. While there may be reasons to justify a locally >>> suboptimal default anyway (such as global consistency), we want to >>> make these choices deliberately, not have them made for us by the >>> accidental details of keyword management. Choosing to leave out a >>> feature for reasons of simplicity is fine; leaving it out because we >>> don't have a way to denote the obvious semantics is not. >>> >>> It may not be obvious from the outside, but this is a constant problem >>> in evolving the language, and an ongoing tax that we all pay, directly >>> or indirectly. >>> >>> ## We need a new source of keyword candidates >>> >>> Every time we confront this problem, the overwhelming tendency is to >>> punt and pick one of the bad options, because the problem only comes >>> along every once in a while. But, with the features in the pipeline, I >>> expect it will continue to come along with some frequency, and I’d >>> rather get ahead of it. Given that all of these current options are >>> problematic, and there is not even a least-problematic move that >>> applies across all situations, my inclination is to try to expand the >>> set of lexical forms that can be used as keywords. >>> >>> As a not-serious example, take the convention that we’ve used for >>> experimental features, where we prefix provisional keywords in >>> prototypes with two underscores, as we did with `__ByValue` in the >>> Valhalla prototype. (We commonly do this in feature proposals and >>> prototypes, mostly to signify “this keyword is a placeholder for a >>> syntax decision to be made later”, but also because it permits a >>> simple implementation that is unlikely to collide with existing code.) >>> We could, for example, carve out the space of identifiers that begin >>> with underscore as being reserved for keywords. Of course, this isn’t >>> so pretty, and it also means we'd have a mix of underscore and >>> non-underscore keywords, so it’s not a serious suggestion, as much as >>> an example of the sort of move we are looking for. >>> >>> But I do have a serious suggestion: allow _hyphenated_ keywords where >>> one or more of the terms are already keywords or reserved identifiers. >>> Unlike restricted keywords, this creates much less trouble for >>> parsing, as (for example) `non-null` cannot be confused for a >>> subtraction expression, and the lexer can always tell with fixed >>> lookahead whether `a-b` is three tokens or one. This gives us a lot >>> more room for creating new, less-conflicting keywords. And these new >>> keywords are likely to be good names, too, as many of the missing >>> concepts we want to add describe their relationship to existing >>> language constructs -- such as `non-null`. >>> >>> Here’s some examples where this approach might yield credible >>> candidates. (Note: none of these are being proposed here; this is >>> merely an illustrative list of examples of how this mechanism could >>> form keywords that might, in some particular possible future, be >>> useful and better than the alternatives we have now.) >>> >>> - `non-null` >>> - `non-final` >>> - `package-private` (the default accessibility for class members, >>> currently not >>> denotable) >>> - `public-read` (publicly readable, privately writable) >>> - `null-checked` >>> - `type-static` (a concept needed in Valhalla, which is static relative >>> to a >>> particular specialization of a class, rather than the class itself) >>> - `default-value` >>> - `eventually-final` (what the `@Stable` annotation currently suggests) >>> - `semi-final` (an alternative to `sealed`) >>> - `exhaustive-switch` (opting into exhaustiveness checking for statement >>> switches) >>> - `enum-class`, `annotation-class`, `record-class` (we might have chosen >>> these >>> as an alternative to `enum` and `@interface`, had we had the option) >>> - `this-class` (to describe the class literal for the current class) >>> - `this-return` (a common request is a way to mark a setter or builder >>> method >>> as returning its receiver) >>> >>> (Again, the point is not to debate the merits of any of these specific >>> examples; the point is merely to illustrate what we might be able to do >>> with such a mechanism.) >>> >>> Having this as an option doesn't mean we can't also use the other >>> approaches when they are suitable; it just means we have more, and >>> likely less fraught, options with which to make better decisions. >>> >>> There are likely to be other lexical schemes by which new keywords can >>> be created without impinging on existing code; this one seems credible >>> and reasonably parsable by both machines and humans. >>> >>> #### "But that's ugly" >>> >>> Invariably, some percentage of readers will have an immediate and >>> visceral reaction to this idea. Let's stipulate for the record that >>> some people will find this ugly. (At least, at first. Many such >>> reactions are possibly-transient (see what I did there?) responses >>> to unfamiliarity.) >>> >>>
