> On 10 Apr 2016, at 11:17, Brent Royal-Gordon <[email protected]> wrote:
>
>> Why not just assign it the correct sign during the init function?
>> (0 ... 6).striding(by: 2) // [0, 2, 4, 6], end > start, so stride = by
>> (6 ... 0).striding(by: 2) // [6, 4, 2, 0], start > end, so stride = -by
>
> 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.
Any thoughts on the alternative I mentioned a little earlier to define
overloads instead of positive/negative? i.e- you would have two methods,
.striding(forwardBy:) and .striding(backwardBy:). 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).
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.
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.
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.
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