[swift-evolution] Int indexing into UTF16View

Tony Allevato tony.allevato at gmail.com
Thu Jun 8 14:35:39 CDT 2017

It is an extremely rare case for a developer to know a priori what literal
numeric indices should be used when indexing into a string, because it only
applies when strings fall into a very specific format and encoding.

It's been discussed before during String-related proposals but AFAIK the
core team has come out against it—it would be an invitation for users who
don't understand the distinction to do very unsafe and wrong things with
strings. IMO, writing your own extension or using index.offset(by:) isn't a
huge penalty here.

On Thu, Jun 8, 2017 at 10:32 AM David Hart via swift-evolution <
swift-evolution at swift.org> wrote:

> Hello,
> When working with Strings which are known to be ASCII, I tend to use the
> UTF16View for the performance of random access. I would also like to have
> the convenience of indexing with Int:
> let barcode = "M1XXXXXXXXX/CLEMENT   EELT9QBQGVAAMSEZY1353 244 21D 531
> 10A1311446838”
> let name = barcode.utf16[2..<22]
> let pnrCode = barcode.utf16[23..<30]
> let seatNo = barcode.utf16[47..<51]
> let fromCity = barcode.utf16[30..<33]
> let toCity = barcode.utf16[33..<36]
> let carrier = barcode.utf16[36..<39]
> let flightNumber = barcode.utf16[39..<44]
> let day = barcode.utf16[44..<47]
> I define my own subscript in an extension to UTF16View but I think this
> should go in the Standard Library.
> Any thoughts?
> David.
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> swift-evolution at swift.org
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