I am persuaded by your argument. I thought we should consider break-return, but I am now convinced that overall break-with is the better choice.
—Guy Sent from my iPhone > On Jan 17, 2019, at 9:45 AM, Remi Forax <fo...@univ-mlv.fr> wrote: > > 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.) >>>> >>>>
