An index that keeps a reference to the collection is an iterator, e.g. the IndexingIterator[1], which String already provides.
[1] https://developer.apple.com/documentation/swift/indexingiterator > On Dec 18, 2017, at 12:53 AM, Cao, Jiannan <frog...@163.com> wrote: > > Or we can copy the design of std::vector::iterator in C++.The index could > keep a reference to the collection. > When the index being offset by + operator, it could call the owner to offset > the index, since it keeps a reference to the collection owner. > > let startIndex = s.startIndex > s[startIndex+1] > > public struct MyIndex<T: Collection> : Comparable where T.Index == MyIndex { > public let owner: T > ... > public static func + (lhs: MyIndex, rhs: T.IndexDistance) -> MyIndex { > return lhs.owner.index(lhs, offsetBy: rhs) > } > } > >> 在 2017年12月15日，上午9:34，Michael Ilseman <milse...@apple.com >> <mailto:milse...@apple.com>> 写道： >> >> Yes, I was trying to highlight that they are different and should be treated >> different. This was because it seemed you were conflating the two in your >> argument. You claim that people expect it, and I’m pointing out that what >> people actually expect (assuming they’re coming from C or languages with a >> similar model) already exists as those models deal in encoded offsets. >> >> More important than expectations surrounding what to provide to a subscript >> are expectations surrounding algorithmic complexity. This has security >> implications. The expectation of subscript is that it is “constant-ish”, for >> a fuzzy hand-wavy definition of “constant-ish” which includes amortized >> constant or logarithmic. >> >> Now, I agree with the overall sentiment that `index(offsetBy:)` is unwieldy. >> I am interested in approaches to improve this. But, we cannot throw linear >> complexity into subscript without extreme justification. >> >> >>> On Dec 14, 2017, at 5:25 PM, Cao, Jiannan <frog...@163.com >>> <mailto:frog...@163.com>> wrote: >>> >>> This offset is unicode offset, is not the offset of element. >>> For example: index(startIndex, offsetBy:1) is encodedOffset 4 or 8, not 1. >>> >>> Offset indexable is based on the offset of count of each element/index. it >>> is the same result of s.index(s.startIndex, offsetBy:i) >>> The encodedOffset is the underlaying offset of unicode string, not the same >>> concept of the offset index of collection. >>> >>> The offset indexable is meaning to the elements and index of collection >>> (i-th element of the collection), not related to the unicode offset (which >>> is the underlaying data offset meaning to the UTF-16 String). >>> >>> These two offset is totally different. >>> >>> Best, >>> Jiannan >>> >>>> 在 2017年12月15日，上午9:17，Michael Ilseman <milse...@apple.com >>>> <mailto:milse...@apple.com>> 写道： >>>> >>>> >>>> >>>>> On Dec 14, 2017, at 4:49 PM, Cao, Jiannan via swift-dev >>>>> <swift-dev@swift.org <mailto:swift-dev@swift.org>> wrote: >>>>> >>>>> People used to the offset index system instead of the String.Index. Using >>>>> offset indices to name the elements, count the elements is normal and >>>>> nature. >>>>> >>>> >>>> The offset system that you’re referring to is totally available in String >>>> today, if you’re willing for it to be the offset into the encoding. That’s >>>> the offset “people” you’re referring to are likely used to and consider >>>> normal and natural. On String.Index, there is the following: >>>> >>>> init(encodedOffset offset: Int >>>> <https://developer.apple.com/documentation/swift/int>) >>>> >>>> and >>>> >>>> var encodedOffset: Int >>>> <https://developer.apple.com/documentation/swift/int> { get } >>>> >>>> >>>> [1] https://developer.apple.com/documentation/swift/string.index >>>> <https://developer.apple.com/documentation/swift/string.index> >>>> >>>> >>>>> This offset index system has a long history and a real meaning to the >>>>> collection. The subscript s[i] has a fix meaning of "getting the i-th >>>>> element in this collection", which is normal and direct. Get the range >>>>> with offset indices, is also direct. It means the substring is from the >>>>> i-th character up to the j-th character of the original string. >>>>> >>>>> People used to play subscript, range with offset indices. Use >>>>> string[string.index(i, offsetBy: 5)] is not as directly and easily as >>>>> string[i + 5]. Also the Range<String.Index> is not as directly as >>>>> Range<Offset>. Developers need to transfer the Range<String.Index> result >>>>> of string.range(of:) to Range<OffsetIndex> to know the exact range of the >>>>> substring. Range<String.Index> has a real meaning to the machine and >>>>> underlaying data location for the substring, but Range<OffsetIndex> also >>>>> has a direct location information for human being, and represents the >>>>> abstract location concept of the collection (This is the most >>>>> UNIMPEACHABLE REASON I could provide). >>>>> >>>>> Offset index system is based on the nature of collection. Each element of >>>>> the collection could be located by offset, which is a direct and simple >>>>> conception to any collection. Right? Even the String with String.Index >>>>> has some offset index property within it. For example: the `count` of the >>>>> String, is the offset index of the endIndex.The enumerated() generated a >>>>> sequence with elements contains the same offset as the offset index >>>>> system provided. And when we apply Array(string), the string divided by >>>>> each character and make the offset indices available for the new array. >>>>> >>>>> The offset index system is just an assistant for collection, not a >>>>> replacement to String.Index. We use String.Index to represent the normal >>>>> underlaying of the String. We also could use offset indices to represent >>>>> the nature of the Collection with its elements. Providing the offset >>>>> index as a second choice to access elements in collections, is not only >>>>> for the String struct, is for all collections, since it is the nature of >>>>> the collection concept, and developer could choose use it or not. >>>>> >>>>> We don't make the String.Index O(1), but translate the offset indices to >>>>> the underlaying String.Index. Each time using subscript with offset >>>>> index, we just need to translate offset indices to underlaying indices >>>>> using c.index(startIndex, offsetBy:i), c.distance(from: startIndex, to:i) >>>>> >>>>> We can make the offset indices available through extension to Collection >>>>> (as my GitHub repo demo: >>>>> https://github.com/frogcjn/OffsetIndexableCollection-String-Int-Indexable- >>>>> >>>>> <https://github.com/frogcjn/OffsetIndexableCollection-String-Int-Indexable->). >>>>> >>>>> or we could make it at compile time: >>>>> for example >>>>> >>>>> c[1...] >>>>> compile to >>>>> c[c.index(startIndex, offsetBy:1)...] >>>>> >>>>> let index: Int = s.index(of: "a") >>>>> compile to >>>>> let index: Int = s.distance(from: s.startIndex, to: s.index(of:"a")) >>>>> >>>>> let index = 1 // if used in s only >>>>> s[index..<index+2] >>>>> compile to >>>>> let index = s.index(s.startIndex, offsetBy: 1) >>>>> s[index..<s.index(index, offsetBy: 2)] >>>>> >>>>> let index = 1 // if used both in s1, s2 >>>>> s1[index..<index+2] >>>>> s2[index..<index+2] >>>>> compile to >>>>> let index = 1 >>>>> let index1 = s1.index(s.startIndex, offsetBy: index) >>>>> let index2 = s2.index(s.startIndex, offsetBy: index) >>>>> s1[index1..<s.index(index1, offsetBy: 2)] >>>>> s2[index2..<s.index(index2, offsetBy: 2)] >>>>> >>>>> I really want the team to consider providing the offset index system as >>>>> an assistant to the collection. It is the very necessary basic concept of >>>>> Collection. >>>>> >>>>> Thanks! >>>>> Jiannan >>>>> >>>>>> 在 2017年12月15日，上午2:13，Jordan Rose <jordan_r...@apple.com >>>>>> <mailto:jordan_r...@apple.com>> 写道： >>>>>> >>>>>> 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@swift.org <mailto:swift-dev@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- >>>>>>> >>>>>>> <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 >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> swift-dev mailing list >>>>>>> swift-dev@swift.org <mailto:swift-dev@swift.org> >>>>>>> https://lists.swift.org/mailman/listinfo/swift-dev >>>>>>> <https://lists.swift.org/mailman/listinfo/swift-dev> >>>>>> >>>>> >>>>> _______________________________________________ >>>>> swift-dev mailing list >>>>> swift-dev@swift.org <mailto:swift-dev@swift.org> >>>>> https://lists.swift.org/mailman/listinfo/swift-dev >>>>> <https://lists.swift.org/mailman/listinfo/swift-dev> >>>> >>> >> >
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