On Tue, Jun 14, 2016 at 12:16 PM, David Waite <da...@alkaline-solutions.com> 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, > 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 < > swift-evolution@swift.org> 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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