On Sat, Jun 11, 2016 at 5:07 PM, Thorsten Seitz <[email protected]> wrote:
> > > Am 11.06.2016 um 23:52 schrieb Xiaodi Wu <[email protected]>: > > On Sat, Jun 11, 2016 at 3:31 PM, Thorsten Seitz <[email protected]> > wrote: > >> >> >> Am 11.06.2016 um 21:57 schrieb Xiaodi Wu <[email protected]>: >> >> On Sat, Jun 11, 2016 at 2:50 PM, Thorsten Seitz <[email protected]> >> wrote: >> >>> >>> >>> Am 10.06.2016 um 17:22 schrieb Erica Sadun via swift-evolution < >>> [email protected]>: >>> >>> >>> On Jun 10, 2016, at 8:02 AM, Xiaodi Wu via swift-evolution < >>> [email protected]> wrote: >>> >>> On Fri, Jun 10, 2016 at 7:18 AM, Haravikk <[email protected]> >>> wrote: >>> >>>> * The word "where" does not consistently imply `break` or `continue`. >>>> In current Swift, `where` implies `break` in the context of a `while` loop >>>> and `continue` in the context of a `for` loop. Some users intuitively guess >>>> the correct meaning in each context, while others guess the wrong meaning. >>>> Therefore, the only way to learn for sure what `where` means in any context >>>> is to read the rulebook. That, by definition, means that this is >>>> unintuitive. >>>> >>>> >>>> This is an argument for renaming the where keyword on for loops to be >>>> more clear, or to somehow integrate continue/break to be more explicit >>>> about what the developer intends for it to do. >>>> >>> >>> Sure: I conclude that the keyword should be *either* removed *or* >>> reformed; both outcomes could address the issue. >>> >>> >>> This is my stance as well and I reserve the right to flit between both >>> choices until we've fully talked it through. >>> >>> One more data point. >>> >>> In the standard library there are just under 950 uses of "for in loops". >>> There are 3 uses of "for in while" : >>> >>> >>> How many of the 950 "for in loops" use a guard with continue? Only these >>> can be compard with the "for in where loops". >>> >> >> That is a different argument, I think, from the one Erica is making. The >> data you're asking about would answer the question, "How often do stdlib >> authors prefer `guard` over `where`?" That is an interesting question, >> certainly. >> >> >> It is the relevant question to ask when deciding whether `where` should >> be better replaced by `guard`. And it should be qualified by asking whether >> the respective author did know about `where`. I wouldn't want a language to >> be designed by looking at usage examples of inexperienced users... >> >> > Here, I disagree with you vehemently. We should absolutely take into > consideration how inexperienced users work with the language. A language > that ignores the struggles and pain points of those who are less > experienced is one that will quickly find itself lacking in users. > > > You don't want to tell me in earnest that discovering and understanding > `where` in for loops are stumbling blocks for beginners in a language > containing generics, associated types, existentials, value vs. reference > types etc.? > I do. I challenge you to find an introductory text that teaches generics, associated types, existentials, or even value vs. reference types before it introduces `for` loops or `if` (and `guard`). > > -Thorsten > > >> I think Erica's point is that what Vladimir earlier called the "simple, >> common" case may be simple but isn't actually common. I did a quick GitHub >> search earlier today (and the tools aren't there, afaik, for an accurate >> regexp search), but what I noticed on a random, not-statistically-sound >> sampling was that uses of `continue` and `break`, when they do occur inside >> a for loop (which isn't always), actually tend to happen after some work >> has been done at the top of the loop. These wouldn't be replaceable by a >> `where` clause. Moreover, I noticed an appreciable share of `return` and >> `fatalError()` calls from inside the loop, which surprised me; I had >> assumed I'd find mostly `break` or `continue`, but even when I did find >> those it was as likely as not to be accompanied by logging. These again >> preclude refactoring into `where`. >> >> >> Logging hints at logic used for filtering out data errors. That's a good >> usage for `guard` as opposed to `where`. The latter is about logic, not >> about error handling. >> >> -Thorsten >> > >
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