On Tue, Jun 14, 2016 at 12:37 PM, Xiaodi Wu <[email protected]> wrote:
> On Tue, Jun 14, 2016 at 12:16 PM, David Waite < > [email protected]> wrote: > >> I’m a bit late to this conversation, and I don’t totally understand the >> goal. >> >> There are a *lot* of things you can do in for…in loop with pattern >> matching that also would supposedly go against this interpretation of >> approachability. Pattern matching in general might be considered to go >> against this interpretation. >> >> Is this pitch saying statements such as: >> >> for i in 1..<100 where i%2 == 1 {…} >> >> should be disallowed, while statements like >> >> for case let view? in views { … } >> >> are still approachable enough to warrant being supported in the language? >> > > Language design has to weigh many factors simultaneously, I think you'd > agree. The argument, essentially, is that `where` is not approachable *for > the functionality that it provides* (namely, as an alternative for a > trivial `guard...continue` statement). Pattern matching is daunting no > doubt, but it offers functionality not conducive to much simpler syntax. > (Or could it be much simpler? If so, then I would support a proposal to > that effect.) > > Put simply, `where` is a less-than-straightforward expression of a very > straightforward concept (filtering an array), whereas pattern matching is > an advanced concept with a commensurately difficult syntax. Others have > brought up generics, for example, but again that's an advanced *concept*; > filtering an array is not. > > >> >> FWIW, I wouldn’t support removing where based on current arguments >> without either the keyword “where" being eliminated completely from the >> language >> > I should add, if this proposal is adopted along with the enclosed suggestion to replace `where` with `if` in `case` and `catch`, the `where` keyword would be completely eliminated except in the context of generics. If the enclosed suggestion is not adopted here, alternatives will follow on shortly. > and/or adding equivalent intuitive functionality to Sequence with >> same-class performance, e.g. a .where(...) equivalent to .lazy.filter(…). >> >> > I feel bad sending clearly passionate people over to crush another > conversation, but I think you'll find in the Swift repository the > beginnings of some explorations by a certain member of the core team to > rename `.filter()` to `.where()` :D > > As to whether certain methods should be lazy or eager by default, that's a > discussion certainly appropriate for this list. > > >> I’ve known about and used the feature since it was first added to Swift >> (learned via the language book), and don’t fully understand the confusion >> that some developers may have - especially since ‘while’ is already a >> keyword and could have been used if that was the actual semantics. >> > > One source of confusion was that `while...where` was supported and had > breaking semantics. Now that's gone with SE-0099. Still, the point is that > `where` is favored by some *because* you don't have to write explicitly > what happens when something doesn't pass the filter, whereas the > counterpoint argument is that not writing explicitly what happens when a > rejected element is encountered *is* the very source of confusion. > > >> >> -DW >> >> On Jun 14, 2016, at 10:32 AM, Xiaodi Wu via swift-evolution < >> [email protected]> wrote: >> >> And from the WWDC Platforms SOTU: "Swift is super simple and >> approachable.... It's great as a first language. And in fact, we think this >> is so important that when we designed Swift this was an explicit design >> goal." >> >> I would be absolutely against adding any more sugar to the for loop. In >> that sense, `where` sets a terrible example that certain features of >> sequences deserve contextual sugar. (And before someone points it out >> again, I've already argued why `for...in` holds its own weight, namely >> difficulty of writing a correct `while` replacement and progressive >> disclosure to the learner so that the concept of iterators can be learned >> afterwards.) >> >> In short, I would very much be opposed to adding keywords "for fun." >> >> >> >
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