I am not sure that macros and annotations would be good, either. It may be impossible to avoid them, given Swift’s goal of “world domination”. Both features are very useful in certain applications.
We could continue to use custom tools like Cog and Sourcery when we need to, or standardize and better integrate their functionality. I honestly am not sure which is a better solution. "Hygienic Macros” and “Annotations” have both been discussed. Both of these features would bring power and complexity to the language, to be sure. I just wanted to voice my opinion that these features, if and when they arrive, should be transparent, i.e., the generated code should be visible and sensibly formatted so that it can be examined and debugged. This would be a hard problem, and I am not sure if it is even possible for complex macro & annotation combinations… C macros are not hygienic and not “transparent”. C preprocessor output, for example, is largely unusable. The uses of macros and annotation overlap. Introducing macros and annotations at the same time would provide a chance to sensibly balance the features of each and provide a coherent set of guidelines for developers. - Chris K > On Jul 30, 2017, at 12:03 PM, Gor Gyolchanyan via swift-evolution > <[email protected]> wrote: > > I don’t think a Cog-like or Gyb-like macro system would be good. That’s > essentially a preprocessor and we all know how that worked out for C. The > only a code-generation feature can exist in a safe language like Swift is by > making it a first-class citizen as described previously. I’m not sure whether > or not the core team would consider such a thing, bit I am very certain that > a text-based macro system is something they’d never consider. > >> On Jul 30, 2017, at 8:54 PM, Christopher Kornher <[email protected] >> <mailto:[email protected]>> wrote: >> >> I assume that the planned “hygienic macro” facility, if it has access to >> metadata, or “annotations", could be used for these sorts of meta tasks, . >> >> This is slightly off-topic, but I hope that there is a way for macros to be >> fully expanded and debuggable (and even formatted). I use Cog with Swift as >> a kind of "macro-system on steroids” that provides these features. I would >> love to see a Cog-like system included as a standard feature of the language >> in the future. It could be a component of annotations, macros, or both. >> >> I would like to see a source code generation pre-pass added for annotations, >> and hopefully macros when they arrive, so that developers can see, debug, >> and code against the expanded code. I realize that may be difficult or even >> impossible for some macros. >> >> GOG uses Python as its macro language, which is certainly compatible with >> Apple’s toolchain. Using a real programming language for annotations, is >> extremely powerful. >> >> The danger of adding a macro system too early, is that it can be used as a >> “cheat” to implement functionality that should be part of the base language >> and discourage language development. I trust that the core team will not let >> this happen. >> >> See Cog: >> https://nedbatchelder.com/code/cog/ <https://nedbatchelder.com/code/cog/> >> >> A fully integrated Cog-like facility this should have language support to >> cleanup the (pretty ugly) delimiters and eventually tool support to >> selectively toggle expansion, as we can today with code blocks, for example, >> in many tools. >> >> I don’t mean to derail this discussion, but it seems that an annotation or >> macro system would be appropriate for this kind of feature. >> >> - Chris >> >> >>> On Jul 30, 2017, at 11:03 AM, Gor Gyolchanyan via swift-evolution >>> <[email protected] <mailto:[email protected]>> wrote: >>> >>> Tino Heth: >>> If you read my reply to Daniel Vollmer, you’ll find that we’re thinking >>> about the exact same thing. Your code snippers show my vision of >>> compiletime beautifully 🙂. >>> Now what I really want at this point is to here the opinions of the core >>> team on this topic. >>> >>> Swift Core Team: >>> Have you guys thought of this? Do you think this is a good idea to put on >>> the table or do you have different plans? >>> >>>> On Jul 30, 2017, at 7:56 PM, Tino Heth <[email protected] <mailto:[email protected]>> >>>> wrote: >>>> >>>> >>>>> more elaborate compile-time facilities, which would also provide >>>>> extremely powerful meta programming features >>>> That's an interesting twist — but whenever you put a "meta" somewhere, >>>> things tend to get complicated, and people end up with different >>>> associations to the topic… ;-) >>>> I took a brief look at the C++ document, but it seemed still to much >>>> macro-like to me. >>>> >>>> My take on the topic would be he ability to express common programming >>>> tasks (declaring a class, overriding a method…) in the language itself. >>>> Imagine >>>> public class ProxyViewController: UIView {} >>>> Could be written as >>>> let subclass = createClass(classname: "ProxyViewController", superclass: >>>> UIViewController, accessLevel: .public) >>>> >>>> Quite stupid at first sight, and basically the exact opposite of syntactic >>>> sugar ("syntactic salt" already has a meaning… so I'd call it "syntactic >>>> pepper" ;-). >>>> But now imagine that: >>>> >>>> for (method, implementation) in UIViewController.methods where >>>> method.accessLevel == .open { >>>> subclass.methods[method] = { parameters in >>>> print("Subclass method \(method) called with \(parameters)") >>>> return implementation(parameters) >>>> } >>>> } >>>> >>>> >>>> Not that stupid anymore, isn't it? >>>> I think this would be way cooler than poking around with variants of >>>> search & replace… >>>> >>>> - Tino >>>> >>>> (to get syntax colouring, I wrote ~30 lines of Swift that turn the straw >>>> man example into valid code… it's fun, maybe I play with it a little bit >>>> more ;-) >>> >>> _______________________________________________ >>> swift-evolution mailing list >>> [email protected] <mailto:[email protected]> >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >> > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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