[swift-evolution] Arrays Returning Optionals instead of Index Out of Bounds

[Rob Norback]

Apologies, please remove the line "Right now myArray[100] = nil gives you
EXC_BAD_INSTRUCTION." from my previous email so it makes more sense to read.

On Mon, Jun 6, 2016 at 12:02 PM Rob Norback <rnorback at gmail.com> wrote:

> First of all, thank you all for bringing me up to date so quickly.  I
> looked over the proposal and it looks awesome.
>
> But as Chris mentioned, this doesn't solve the expected behavior and
> ambiguity of ```Array<Int?>```
>
> In this case I would expect the default behavior (myArray[4]) without
> using myArray[checking: 4] should return a nil in this case.
>
> And Chris, I think it would make the most sense to have myArray[0] = nil
> to be stored if the index is in Range, and for myArray[100] = nil to give a
> warning of no assignment being made because index is out of range, kind of
> like an unused variable.  Right now myArray[100] = nil gives you
> EXC_BAD_INSTRUCTION.  Then if you assigned myArray[100] = 200, that would
> have to simply change the Range.
>
> Chris, I honestly have to think more about that ambiguity with
> dictionaries.
>
> I can see that this would definitely need some further fleshing out, but
> it seems to be sufficiently different from Luis' proposal to perhaps merit
> it's own proposal.
>
> It's up to you Luis, but I think this might be a bit more controversial
> then the changes you've proposed, making it possible for your proposal
> getting rejected.  (I want your proposal accepted, since I would use those
> features today).  Partial acceptance of a proposal doesn't seem to be a
> thing. (Once again please correct me if I'm wrong).
>
> On Mon, Jun 6, 2016 at 11:46 AM Luis Henrique B. Sousa <lshsousa at gmail.com>
> wrote:
>
>> Thanks Vladimir,
>>
>> The correct link is this one (with the additional min/max operations in
>> the implementation):
>>
>> https://github.com/luish/swift-evolution/blob/proposal-lenient-collection-subscripts/proposals/nnnn-more-lenient-collections-subscripts.md
>>
>> Here is the pull request on the swift-evolution repo:
>> https://github.com/apple/swift-evolution/pull/328
>>
>> Any help or suggestion to improve the proposal is welcome. :-)
>>
>> - Luis
>>
>> On Mon, Jun 6, 2016 at 6:10 PM, Vladimir.S via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>> Please find this draft of proposal(hope this is correct link for latest
>>> version):
>>>
>>> https://github.com/luish/swift-evolution/blob/more-lenient-subscripts/proposals/nnnn-more-lenient-collections-subscripts.md
>>>
>>> The main idea is to introduce 2 new subscript methods:  [clamping:] and
>>> [checking:]
>>>
>>> There was discussion in "[Proposal] More lenient subscript methods over
>>> Collections" and (older) "[Proposal] Safer half-open range operator"
>>>
>>>
>>> On 06.06.2016 19:50, Rob Norback via swift-evolution wrote:
>>>
>>>> Hi Everyone!
>>>>
>>>> This is my first time emailing the swift evolution list, so if this
>>>> topic
>>>> has already been discussed please let me know.  I looked through all the
>>>> accepted and rejected proposals and it doesn't seem to be on there.
>>>>
>>>> The main thought is that dictionaries return optionals, so why not
>>>> arrays?
>>>> Or other CollectionTypes for that matter.  I would think this would be
>>>> the
>>>> expected behavior in this situation:
>>>>
>>>> var myArray:[String?] = []
>>>> print(myArray[4])
>>>> // EXC_BAD_INSTRUCTION, but could just be Optional(nil)
>>>>
>>>> Then you could do things like
>>>>
>>>> if let arrayValue = myArray[4] {
>>>>    // do something
>>>> }
>>>>
>>>> Of course you could simply check with with the count, but considering
>>>> Swift's use of optionals to represent empty variables rather than
>>>> erroring
>>>> out or returning an empty String, I think this functionality would be
>>>> appropriate to include in the Swift standard library.
>>>>
>>>> And there's about 15,000 people who've looked for this functionality in
>>>> the
>>>> last year:
>>>>
>>>> http://stackoverflow.com/questions/25329186/safe-bounds-checked-array-lookup-in-swift-through-optional-bindings
>>>> .
>>>>
>>>> Please let me know what you think.
>>>>
>>>> Best,
>>>> Rob Norback
>>>>
>>>>
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>>>>
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>>>
>>
>>
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