[swift-evolution] [Pitch] Enumerate from offset

[Pavol Vaskovic]

(I forgot to reply-all to mailing list, sorry for double posting Ben!)


On Thu, May 4, 2017 at 8:11 PM, Ben Cohen via swift-evolution <
swift-evolution at swift.org> wrote:

>
> On May 4, 2017, at 10:15 AM, Jaden Geller via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> It's been suggested by a core team member that enumerated itself might not
> hold its weight in the standard library. Instead, we ought to write
> `zip(foo.indices, foo)` or `zip(0..., foo)`. It's easier for the caller to
> see which side of the tuple stores the index and whether the index is an
> integer or an actual index type. This use case seems to further support
> this design since `zip(x…, foo)` and `zip(foo.indicies.drop(x), foo)` can
> be easily written.
>
>
> Yup, this is my personal preference. Enumerated has a number of
> correctness and usability issues: slices aren’t zero based so you could
> miss a potential trap at runtime, order of the two arguments is unclear
> unlike the zip alternative, and it encourages people to write code using
> integers rather than indices even one the latter is more expressive and
> generalizes better if you ever want to make what you wrote generic.
>
> Note also, since SE-0172 is now implemented on master, you can also write
> zip(6…, myArray) if you want to alter the starting value.
>

I have mentioned this in Alternatives considered section, with following
comment:

> Drawback of this approach is that you need to use free function zip,
forcing a break in the chain of sequence operations, as there is currently
no zipped method on Sequence.

> If this is the preffered approach, we should consider removing the
enumerated() method altogether, because the limited usefullness in its
current state hardly justifies the space on API surface it occupies.

I'd be personally fine with removal of enumerated() if we added
zipped(with:).
Free function zip is essential, no doubt. What was the reason there isn't
also zipped, Ben?

--Pavol
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