[swift-dev] Make offset index available for String

[Kelvin Ma]

I think there’s a middle ground here as the current API is overly complex
and general. 95% of the time people are dealing with ASCII strings and
don’t care about things like unicode cluster boundaries and whatnot

On Thu, Dec 14, 2017 at 12:13 PM, Jordan Rose via swift-dev <
swift-dev at swift.org> wrote:

> We really don't want to make subscripting a non-O(1) operation. That just
> provides false convenience and encourages people to do the wrong thing with
> Strings anyway.
>
> I'm always interested in why people want this kind of ability. Yes, it's
> nice for teaching programming to be able to split strings on character
> boundaries indexed by integers, but where does it come up in real life? The
> most common cases I see are trying to strip off the first or last
> character, or a known prefix or suffix, and I feel like we should have
> better answers for those than "use integer indexes" anyway.
>
> Jordan
>
>
> On Dec 13, 2017, at 22:30, Cao, Jiannan via swift-dev <swift-dev at swift.org>
> wrote:
>
> Hi,
>
> I would like to discuss the String.Index problem within Swift. I know the
> current situation of String.Index is based on the nature of the underlaying
> data structure of the string.
>
> But could we just make String.Index contain offset information? Or make
> offset index subscript available for accessing character in String?
>
> for example:
>
> let a = "01234"
> print(a[0]) // 0
> print(a[0...4]) // 01234
> print(a[...]) // 01234
> print(a[..<2]) // 01
> print(a[...2]) // 012
> print(a[2...]) // 234
> print(a[2...3]) // 23
> print(a[2...2]) // 2
> if let number = a.index(of: "1") {
>     print(number) // 1
>     print(a[number...]) // 1234
> }
>
>
>
> 0 equals to Collection.Index of collection.index(startIndex, offsetBy: 0)
> 1 equals to Collection.Index of collection.index(startIndex, offsetBy: 1)
> ...
> we keep the String.Index, but allow another kind of index, which is called
> "offsetIndex" to access the String.Index and the character in the string.
> Any Collection could use the offset index to access their element,
> regarding the real index of it.
>
> I have make the Collection OffsetIndexable protocol available here, and
> make it more accessible for StringProtocol considering all API related to
> the index.
>
> https://github.com/frogcjn/OffsetIndexableCollection-String-Int-Indexable-
>
> If someone want to make the offset index/range available for any
> collection, you just need to extend the collection:
>
> extension String : OffsetIndexableCollection {
> }
> extension Substring : OffsetIndexableCollection {
> }
>
>
>
> I hope the Swift core team could consider bring the offset index to
> string, or make it available to other collection, thus let developer to
> decide whether their collection could use offset indices as an assistant
> for the real index of the collection.
>
>
> Thanks!
> Jiannan
>
>
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