<div style="white-space:pre-wrap">What types do you have in mind that would only support positive distances? All numeric types (yes, even UInt, etc.) have signed distances, which reflects the basic mathematical abstraction of a number line.<br><br>A consistent behavior with signed distances is so important that we are currently struggling with an interesting issue with floating point types, which is that due to rounding error 10.0 + a - a != 10.0 for some values of a.<br></div><br><div class="gmail_quote"><div dir="ltr">On Sun, Apr 10, 2016 at 12:53 PM Haravikk via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><br><div><blockquote type="cite"><div>On 10 Apr 2016, at 11:17, Brent Royal-Gordon <<a href="mailto:brent@architechies.com" target="_blank">brent@architechies.com</a>> wrote:</div><div><br><blockquote type="cite">Why not just assign it the correct sign during the init function?<br>(0 ... 6).striding(by: 2) // [0, 2, 4, 6], end > start, so stride = by<br>(6 ... 0).striding(by: 2) // [6, 4, 2, 0], start > end, so stride = -by<br></blockquote><br>One reason not to do it this way is that, if we extend `striding(by:)` to other collections, they will not be as easy to walk backwards through as this. You will have to do something like `collection.reversed().striding(by:)` which will be a hassle.</div></blockquote><br></div></div><div style="word-wrap:break-word"><div>Any thoughts on the alternative I mentioned a little earlier to define overloads instead of positive/negative? i.e- you would have two methods, <font face="Menlo">.striding(forwardBy:)</font> and <font face="Monaco">.striding(backwardBy:)</font>. In addition to eliminating the use of a negative stride to indicate direction, this has the advantage that .striding(backwardBy:) can be defined only for types with a ReverseIndex or only for collections (as you can stride through a sequence, but only by going forward).</div><div><br></div><div>This should also make documentation a bit clearer, otherwise you’ve got the caveat that to go backwards requires a negative value, but only if the type supports that, which a developer would then need to check. Instead it either has the backwardBy variant or not.</div><div><br></div><div>I know that advance(by:) supports negative values, but this is actually something I wouldn’t mind seeing changed as well, as it has the same issues (passing a negative value in looks fine until you realise the type is a ForwardIndex only). It would also allow us to define Distance types that don’t support a direction, since this would be given by the choice of method called instead.</div><div><br></div><div><br></div><div>Of course I’d still like to be able to define 6 … 0 or whatever, but this would at least eliminate what I dislike about using negatives for direction.</div></div>_______________________________________________<br>
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