[swift-evolution] [Proposal] More lenient subscript methods over Collections
Luis Henrique B. Sousa
lshsousa at gmail.com
Tue May 17 17:18:47 CDT 2016
Many thanks, @Maximilian. I'm also not sure about the performance cost, but
I think it is worth it.
So I just updated the proposal also including the additional min/max you
have suggested (thanks once again):
https://github.com/apple/swift-evolution/pull/328
Best regards,
- Luis
On Tue, May 17, 2016 at 10:32 PM, Maximilian Hünenberger <
m.huenenberger at me.com> wrote:
> While it is true that it uses min and max, you have to add *additional
> min max* in order to achieve the desired behavior.
>
> So the implementation should be: (also considering (hopefully all) recent
> naming/index model updates)
>
> // Index is already Comparable
> extension Collection {
>
> subscript(clamping range: Range<Index>) -> SubSequence {
> // ---> here you have to use the additional min/max
> let start = min(max(startIndex, range.startIndex), endIndex)
> let end = max(min(endIndex, range.endIndex), startIndex)
> return self[start ..< end]
>
> // ---> or as alternative, probably a bit less performant but
> Swiftier
> return self[range.clamping(startIndex..<endIndex)]
> }
>
> subscript(checking range: Range<Index>) -> SubSequence? {
> guard range.startIndex >= startIndex && range.endIndex <= endIndex
> else { return nil }
> return self[range]
> }
>
> subscript(checking index: Index) -> Generator.Element? {
> // ---> minor syntax update *
> guard self.indices.contains(index)
> else { return nil }
> return self[index]
> }
>
> }
>
> * I'm not sure it is worth the performance cost for arbitrary indices
> collection with O(n) search. I could imagine Set and Dictionary indices
> cannot be easily validated in comparison to Array indices. However this
> approach is more general and handles non trivial index collections where
> there is no guarantee that any index between startIndex and endIndex is a
> valid one.
> The same arguments also apply to `subscript(checking range ...)` where you
> could validate start and endIndex of the range.
>
> Best regards
> Maximilian
>
> Am 16.05.2016 um 09:45 schrieb Luis Henrique B. Sousa <lshsousa at gmail.com
> >:
>
> Yes. The suggested implementation does use min/max:
>
>
> https://github.com/luish/swift-evolution/blob/more-lenient-subscripts/proposals/nnnn-more-lenient-collections-subscripts.md#detailed-design
>
> - Luis
>
> On Sun, May 15, 2016 at 3:42 PM, Maximilian Hünenberger <
> m.huenenberger at me.com> wrote:
>
>> I brought these up because the current implementation produces an error
>> in these cases. You have to insert additional min/max operations.
>>
>> Am 15.05.2016 um 16:38 schrieb Luis Henrique B. Sousa <lshsousa at gmail.com
>> >:
>>
>> Exactly, the idea is to return an empty array just like other languages
>> do. (e.g. python)
>>
>> - Luis
>>
>> On Sun, May 15, 2016 at 10:13 AM, Vladimir.S via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>> On 15.05.2016 0:09, Maximilian Hünenberger via swift-evolution wrote:
>>>
>>>> One point which should be discussed is the following behaviour:
>>>>
>>>> let array = [0]
>>>> // ranges are completely out of bounds and produce an error
>>>> array[clamping: 1...2] // error
>>>> array[clamping: -2...-1] // error
>>>>
>>>> Should a range which has no intersection with the indices of the
>>>> collection
>>>> produce an error or just clamp to 0..<0 respectively
>>>> endIndex..<endIndex?
>>>>
>>>
>>> I expect it will returns [] i.e. empty array, as no elements with
>>> 1...2(-2..-1) indexes in the array. I understand `clamping` similar as
>>> 'bounded','in these bounds'. And as soon as [0,1,2,3,4][clamping:2...10]
>>> will silently move the right position to allowed index(4), and
>>> [0,1,2,3,4][clamping:-2...0] will move left position to 0, I expect that
>>> in [0][clamping: 1...2] will try to move both limits to allowed, and as no
>>> intersection - silently return empty array.
>>>
>>>
>>>> Best regards
>>>> Maximilian
>>>>
>>>> Am 13.05.2016 um 17:10 schrieb Luis Henrique B. Sousa via
>>>> swift-evolution
>>>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>:
>>>>
>>>> It seems that there is a consensus that this proposal might be a good
>>>>> addition to the standard library. All comments on this thread in the
>>>>> past
>>>>> few weeks were related to naming, not around the behaviour or validity
>>>>> of
>>>>> the proposed methods. So I will submit this proposal for review very
>>>>> soon
>>>>> assuming that nobody else has strong arguments against it. :-)
>>>>>
>>>>> Proposal:
>>>>> https://github.com/luish/swift-evolution/blob/more-lenient-subscripts/proposals/nnnn-more-lenient-collections-subscripts.md
>>>>>
>>>>> If you have any corrections or suggestions to the proposal text itself,
>>>>> please comment on this gist:
>>>>> https://gist.github.com/luish/832c34ee913159f130d97a914810dbd8
>>>>> (or pull request to my repo)
>>>>>
>>>>> Regards,
>>>>>
>>>>> - Luis
>>>>>
>>>>> On Tue, May 10, 2016 at 4:13 PM, Luis Henrique B. Sousa
>>>>> <lshsousa at gmail.com <mailto:lshsousa at gmail.com>> wrote:
>>>>>
>>>>> Please let me know if you have more suggestions or corrections on
>>>>> this proposal.
>>>>> I'm tempted to submit it for review. :-)
>>>>>
>>>>> - Luis
>>>>>
>>>>> On Tue, May 10, 2016 at 8:53 AM, Luis Henrique B. Sousa
>>>>> <lshsousa at gmail.com <mailto:lshsousa at gmail.com>> wrote:
>>>>>
>>>>> It sounds good, thanks for you suggestions @Vladimir, @Patrick
>>>>> and @Brent.
>>>>>
>>>>> I've just updated the proposal:
>>>>>
>>>>> https://github.com/luish/swift-evolution/blob/more-lenient-subscripts/proposals/nnnn-more-lenient-collections-subscripts.md#detailed-design
>>>>>
>>>>> - Luis
>>>>>
>>>>> On Tue, May 10, 2016 at 6:50 AM, Vladimir.S via swift-evolution
>>>>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>
>>>>> wrote:
>>>>>
>>>>> Yes, I feel like 'within' is much better than 'bounded'.
>>>>>
>>>>> How about such changes in proposal:
>>>>>
>>>>> a[bounded: -1 ..< 5] --> a[within: -1 ..< 5] (or
>>>>> a[inside:
>>>>> -1 ..< 5] )
>>>>>
>>>>> a[optional: 0 ..< 5] --> a[checking: 0 ..< 5]
>>>>> a[optional: 5] --> a[checking: 5]
>>>>>
>>>>> ?
>>>>>
>>>>> On 10.05.2016 6:27, Patrick Smith via swift-evolution
>>>>> wrote:
>>>>>
>>>>> I like the idea of the of the bounded subscript,
>>>>> however
>>>>> the optional one I
>>>>> feel could be used for clumsy code.
>>>>>
>>>>> .first and .last have value, but once you start
>>>>> stepping
>>>>> several arbitrary
>>>>> indices in, then that code is likely fragile?
>>>>>
>>>>>
>>>>> I can think of ‘within’, ‘inside’ and ‘intersecting’ as
>>>>> alternative names
>>>>> for ‘bounded’ that attempt to explain what is going on:
>>>>>
>>>>> let a = [1, 2, 3]
>>>>>
>>>>> a[within: 0 ..< 5] // [1, 2, 3]
>>>>> a[inside: 0 ..< 5] // [1, 2, 3]
>>>>> a[intersecting: 0 ..< 5] // [1, 2, 3]
>>>>>
>>>>>
>>>>> On 28 Apr 2016, at 10:11 PM, Luis Henrique B. Sousa
>>>>> via swift-evolution
>>>>> <swift-evolution at swift.org
>>>>> <mailto:swift-evolution at swift.org>
>>>>> <mailto:swift-evolution at swift.org
>>>>> <mailto:swift-evolution at swift.org>>> wrote:
>>>>>
>>>>> As we have discussed throughout this thread, the
>>>>> initial proposal was
>>>>> modified to include alternative subscript methods
>>>>> instead of modifying
>>>>> the default operator/subscript behaviour.
>>>>> The first draft is
>>>>> here:
>>>>>
>>>>> https://github.com/luish/swift-evolution/blob/more-lenient-subscripts/proposals/nnnn-more-lenient-collections-subscripts.md
>>>>>
>>>>> I've also put this as a gist so that you can leave
>>>>> comments with respect
>>>>> to the proposal document itself. Any suggestion or
>>>>> help is very welcome.
>>>>>
>>>>> https://gist.github.com/luish/832c34ee913159f130d97a914810dbd8
>>>>>
>>>>> Regards,
>>>>>
>>>>> - Luis
>>>>>
>>>>> On Mon, Apr 11, 2016 at 1:23 PM, Luis Henrique B.
>>>>> Sousa
>>>>> <lshsousa at gmail.com <mailto:lshsousa at gmail.com>
>>>>> <mailto:lshsousa at gmail.com
>>>>>
>>>>> <mailto:lshsousa at gmail.com>>> wrote:
>>>>>
>>>>> This proposal seeks to provide a safer ..< (aka
>>>>> half-open range
>>>>> operator) in order to avoid **Array index out
>>>>> of
>>>>> range** errors in
>>>>> execution time.
>>>>>
>>>>> Here is my first draft for this proposal:
>>>>>
>>>>>
>>>>> https://github.com/luish/swift-evolution/blob/half-open-range-operator/proposals/nnnn-safer-half-open-range-operator.md
>>>>>
>>>>> In short, doing that in Swift causes a runtime
>>>>> error:
>>>>>
>>>>> leta =[1,2,3]
>>>>> letb =a[0..<5]
>>>>> print(b)
>>>>>
>>>>> > Error running code:
>>>>> > fatal error: Array index out of range
>>>>>
>>>>> The proposed solution is to slice the array
>>>>> returning all elements
>>>>> that are below the half-open operator, even
>>>>> though the number of
>>>>> elements is lesser than the ending of the
>>>>> half-open operator. So the
>>>>> example above would return [1,2,3].
>>>>> We can see this very behaviour in other
>>>>> languages, such as Python and
>>>>> Ruby as shown in the proposal draft.
>>>>>
>>>>> This would eliminate the need for verifications
>>>>> on the array size
>>>>> before slicing it -- and consequently runtime
>>>>> errors in cases when
>>>>> the programmer didn't.
>>>>>
>>>>> Viewing that it is my very first proposal, any
>>>>> feedback will be helpful.
>>>>>
>>>>> Thanks!
>>>>>
>>>>> Luis Henrique Borges
>>>>> @luishborges
>>>>>
>>>>>
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>>>>> <mailto:swift-evolution at swift.org>>
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