OK, but how do you use IndexingIterator to get element and not change itself?
In C++, the iterator is more like index. because it could be used to get the
element, and not change itself, and it can be offset back and forth not only by
one.
*it
*(it+5)
*(it-5)
but in Swift,
you can only using next() to get the element and change the iterator to point
to the next item:
it.next()
it.next()
it.next()
it.next()
it.next()
and you could not go to previous item.
The iterator in Swift could not be used as index.
> 在 2017年12月19日，上午3:00，Michael Ilseman <milse...@apple.com
> <mailto:milse...@apple.com>> 写道：
>
> 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
> <https://developer.apple.com/documentation/swift/indexingiterator>
>
>
>> On Dec 18, 2017, at 12:53 AM, Cao, Jiannan <frog...@163.com
>> <mailto: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-...@swift.org <mailto:swift-...@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-...@swift.org <mailto:swift-...@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-...@swift.org <mailto:swift-...@swift.org>
>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-dev
>>>>>>>> <https://lists.swift.org/mailman/listinfo/swift-dev>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> swift-dev mailing list
>>>>>> swift-...@swift.org <mailto:swift-...@swift.org>
>>>>>> https://lists.swift.org/mailman/listinfo/swift-dev
>>>>>> <https://lists.swift.org/mailman/listinfo/swift-dev>
>>>>>
>>>>
>>>
>>
>
_______________________________________________
swift-users mailing list
swift-users@swift.org
https://lists.swift.org/mailman/listinfo/swift-users
