[swift-evolution] Optional safe subscripting for arrays

[davesweeris at mac.com]

In principle, I’m not opposed to that. In practice, though… unless you’re also proposing we give it “magic” syntax like what Optionals currently have, we’d have to manually wrap/unwrap the values:
bar[ifExists: 3] = Result.result(4)
print(bar[ifExists: 4].result)

Which would strictly speaking work, but IMHO is more annoying than just manually checking collection.indices.contains(idx) before attempting the subscript.

- Dave Sweeris

> On Feb 6, 2016, at 13:21, Thorsten Seitz via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Ah ok, I was using the other version which distinguishes between nil and Optional(nil):
> 
> extension Array {
>     subscript(ifExists idx: Index) -> Element? {
>         get { return (startIndex ..< endIndex) ~= idx ? self[idx] : nil }
>         set { if (startIndex ..< endIndex) ~= idx && newValue != nil { self[idx] = newValue! } }
>     }
> }
> 
> Where you can assign Optional(nil) to set a value to nil which is admittedly not very intuitive...
> 
> var array: [Int?] = [1]
> array[ifExists: 0] = Optional(nil)
> print(array) // "[nil]"
> array = [1]
> array[ifExists: 0] = array[ifExists: 1]
> print(array) // "[Optional(1)]"
> 
> A solution would probably be to introduce another enum mimicking Optional but built for the array subscript which allows to distinguish both cases.
> 
> -Thorsten 
> 
> Am 06.02.2016 um 21:52 schrieb Maximilian Hünenberger <m.huenenberger at me.com <mailto:m.huenenberger at me.com>>:
> 
>> var array: [Int?] = [1]
>> array[ifExists: 0] = nil // sets array[0] to nil if index is valid
>> print(array) // "[nil]"
>> array = [1]
>> array[ifExists: 0] = array[ifExists: 1]
>> print(array) // "[nil]"
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