> On 15 Jun 2017, at 19:28, Chris Lattner <sa...@nondot.org> wrote: > > > On Jun 15, 2017, at 9:41 AM, Xiaodi Wu via swift-evolution > <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> o >>> > >>> > let (a : Int, b : Float) = foo() >>> >>> >>> I think it would be better if the compiler raised a warning whenever you >>> tried to redefine a builtin type. >>> >>> That’s essentially my preferred solution as well, as it gets to the root of >>> the confusion. >>> >>> Naming a variable the same as a type should be similar to naming a variable >>> the same as a reserved keyword and require backticks. (A previous >>> suggestion to enforce capitalization falls down with full Unicode support >>> and complicates interop where imported C structures might be lowercase and >>> constants might be all caps.) No need to treat built-in types specially; >>> it’s equally a problem with types imported from other libraries, which can >>> be shadowed freely today. For full source compatibility this can be a >>> warning instead of an error–should be sufficient as long as it’s brought to >>> the user’s attention. In fact, probably most appropriate as a warning, >>> since the _compiler_ knows exactly what’s going on, it’s the human that >>> might be confused. >> >> I kind of agree with all you say. But I also feel that tuple element names >> in patterns are very rarely used and not worth the added complexity and >> confusing. Going back to the old: “Would be add it to Swift if it did not >> exist?”, I would say no. >> >> That was the standard for removing features before Swift 3, but with source >> compatibility the bar is now much higher. > > Completely agreed. My belief on this is that it is a legacy Swift 1 type > system capability that no one uses. I have no data to show that though. > >> Is the feature harmful? > > Yes, absolutely. The shadowing isn't the thing that bothers me, it is that > swift has a meaning for that very syntax in other contexts, and that this is > completely different meaning. People absolutely would get confused by this > if they encountered it in real code that they themselves didn't write, and > I'm not aware of any good (non theoretical) use for it. > >> My point is, not on its own it isn’t: warning on variables shadowing types >> is sufficient to resolve the problems shown here. > > Again, my concern is that this is a confusing and misleading feature which > complicates and potentially prevents composing other features in the future. > > >> >> How strange that we’re talking about this issue in a thread about SE-0110. > > This came up in the discussion about 110 because we were exploring whether it > was plausible to expand the function parameter grammar to support > destructuring in the position where a name goes. There are many concerns > about whether this is a good idea, but he existence of this in the tuple > destructuring pattern grammar is pretty much a showstopper. > >> If anything, the response to that proposal should be a cautionary tale that >> users can take poorly to removing features, sometimes in unanticipated ways. > > Agreed, it may be too late to correct this (certainly we can't outright > remove it in Swift 4 if someone is using it for something important). > However if it turns out that it really isn't used, then warning about it in 4 > and removing it shortly after may be possible.
And I think its difficult to make the parallel between the two. SE-0110 basically impacted everybody calling higher-order functions on Dictionary (+ more users from libraries like RxSwift), which makes an enormous proportion of the Swift community. On the other hand, despite the enormous amount of time I have sinked into learning, discussing and enjoying Swift, I never come upon the tuple element name syntax in patterns until Robert pointed to it out on twitter several weeks ago. > -Chris > >> >>> `let (a : Int, b : Float) = foo()` is confusing but if you were to use your >>> own type (e.g., `struct S {}` and replace Int and Float with S) you would >>> get a compiler error. If the compiler warned you that you were reassigning >>> Int and Float, you’d probably avoid that problem. Or, for a more extreme >>> fix, we could make reassigning builtin types illegal since there is pretty >>> much no valid reason to do that. >>> >>> >>> > On Jun 15, 2017, at 8:10 AM, Matthew Johnson via swift-evolution >>> > <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>> > >>> > >>> > >>> > Sent from my iPad >>> > >>> >> On Jun 14, 2017, at 11:01 PM, Chris Lattner via swift-evolution >>> >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>> >> >>> >> >>> >>> On Jun 12, 2017, at 10:07 PM, Paul Cantrell <cantr...@pobox.com >>> >>> <mailto:cantr...@pobox.com>> wrote: >>> >>> >>> >>> What’s the status of this Chris’s double parens idea below? It garnered >>> >>> some positive responses, but the discussion seems to have fizzled out. >>> >>> Is there something needed to help nudge this along? >>> >>> >>> >>> What’s the likelihood of getting this fixed before Swift 4 goes live, >>> >>> and the great wave of readability regressions hits? >>> >> >>> >> We discussed this in the core team meeting today. Consensus seems to be >>> >> that a change needs to be made to regain syntactic convenience here. >>> >> Discussion was leaning towards allowing (at least) the parenthesized >>> >> form, but more discussion is needed. >>> >> >>> >> >>> >> One (tangential) thing that came up is that tuple element names in tuple >>> >> *patterns* should probably be deprecated and removed at some point. >>> >> Without looking, what variables does this declare?: >>> >> >>> >> let (a : Int, b : Float) = foo() >>> > >>> > Another option would be to require let to appear next to each name >>> > binding instead of allowing a single let for the whole pattern. I >>> > personally find that much more clear despite it being a little bit more >>> > verbose. >>> > >>> >> >>> >> ? >>> >> >>> >> -Chris >>> >> >>> >> _______________________________________________ >>> >> swift-evolution mailing list >>> >> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> >> https://lists.swift.org/mailman/listinfo/swift-evolution >>> >> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>> > >>> > _______________________________________________ >>> > swift-evolution mailing list >>> > swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> > https://lists.swift.org/mailman/listinfo/swift-evolution >>> > <https://lists.swift.org/mailman/listinfo/swift-evolution> >>> >>> _______________________________________________ >>> swift-evolution mailing list >>> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>> _______________________________________________ >>> swift-evolution mailing list >>> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-evolution >> <https://lists.swift.org/mailman/listinfo/swift-evolution>
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