> 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... > > 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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