[swift-users] Subsequences and shared indices

Tim Vermeulen tvermeulen at me.com
Thu Oct 13 19:42:53 CDT 2016

Alright. Does this mean that we can otherwise assume that collections share indices with their subsequences? It might be worth documenting, one way or the other.

> On 14 Oct 2016, at 02:40, Hooman Mehr <hooman at mac.com> wrote:
> This is a bug reported multiple times in different forms. My version of it is: SR-1487 <https://bugs.swift.org/browse/SR-1487>. 
> It remains open because it is not easy to fix with the existing design of String. Apparently core standard library team are working on an overhaul of String to address this and other usability and performance issues.
>> On Oct 13, 2016, at 5:12 PM, Tim Vermeulen via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> Is it a requirement that collections share indices with its subsequence? Array and ArraySlice do share indices, which is why ArraySlice isn’t zero-based, and I think this is convenient. But String.CharacterView doesn’t seem to share indices with its subsequence (which is String.CharacterView as well). Consider this example:
>> let foo = "foobar".characters
>> let index = foo.index(foo.startIndex, offsetBy: 3)
>> let bar = foo.suffix(from: index)                   // "bar"
>> foo[index]                                          // "b" :)
>> foo[bar.startIndex]                                 // "f" :(
>> So does this mean that we can’t assume that collections and their subsequences share their indices (which could be very handy),  or is this just a bug related to String.CharacterView?
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>> swift-users at swift.org <mailto:swift-users at swift.org>
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