[swift-evolution] Optional safe subscripting for arrays

[Rudolf Adamkovič]

Hi Maximilian,

ah, I see. This is a show stopper then!

From what I imagine, this should not type-check:

var array = [1]
array[ifExists: 0] = nil

… and this should set array[0] to nil:

var array: [Int?] = [1]
array[ifExists: 0] = nil

Is it not possible to implement such setter in Swift?

R+

> On 1 Feb 2016, at 00:07, Maximilian Hünenberger <m.huenenberger at me.com> wrote:
> 
> The setter of the subscript should be:
> 
> set {
>     if self.indices ~= index && newValue != nil {
>         self[index] = newValue!
>     }
> }
> 
> Since "newValue" is of type "Element?".
> 
> It seems that this subscript could also be added to "CollectionType" and "MutableCollectionType".
> 
> The setter is weird because you can use an optional element:
> 
> var arr = [1]
> // is valid but doesn't set the first element
> arr[ifExists: 0] = nil
> 
> var arr2: [Int?] = [1]
> arr2[ifExists: 0] = nil // changes nothing
> arr2[ifExists: 0] = .Some(nil) // sets first element to nil : arr2 == [nil]
> 
> I don't know whether a setter should be added at all.
> 
> - Maximilian
> 
> Am 31.01.2016 um 23:38 schrieb Rudolf Adamkovič via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>:
> 
>> All right, I put together a proposal:
>> 
>> https://github.com/salutis/swift-evolution/blob/master/proposals/XXXX-runtime-safe-array-subscripting.md <https://github.com/salutis/swift-evolution/blob/master/proposals/XXXX-runtime-safe-array-subscripting.md>
>> 
>> … and opened a PR:
>> 
>> https://github.com/apple/swift-evolution/pull/133 <https://github.com/apple/swift-evolution/pull/133>
>> 
>> Let’s see how this goes.
>> 
>> R+

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