[swift-evolution] [Proposal] More lenient subscript methods over Collections

Sat May 14 16:09:01 CDT 2016

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?

Best regards
Maximilian

> Am 13.05.2016 um 17:10 schrieb Luis Henrique B. Sousa via swift-evolution <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> 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> 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> 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>> 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>> 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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>>>>> 
>>>>> 
>>>>> 
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