[swift-evolution] Optional Setting

[James Campbell]

If it has a value already the nit wouldn't call anything as it technically
hasn't been set. Only if it already has a value does it try and set
something in which case the didSet is called :)

On Tue, Dec 15, 2015 at 11:16 PM, Jacob Bandes-Storch via swift-evolution <
swift-evolution at swift.org> wrote:

> One possible caveat is with custom setters.
>
> If "a" already has a value, does "a ??= b" call the custom
> setter/willSet/didSet, or does it see the nil and short-circuit?
>
> This can be implemented today:
>
>     func ??=(inout lhs: T?, @autoclosure rhs: () -> T?) { if lhs == nil {
> lhs = rhs() } }
>
> However, the use of "inout" will always cause the didSets to be triggered
> at the call site, when just using if-statements instead wouldn't have done
> so.
>
> Jacob
>
> On Tue, Dec 15, 2015 at 3:10 PM, Brent Royal-Gordon via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> > I think that the existing syntax for “??” handles this need fairly well
>> without requiring an additional assignment operator:
>> >
>> >       a = a ?? []
>>
>> When the variable is `a`, sure. When it’s
>> `scoreboardViewController.selectedScoreboard`, not so much.
>>
>> +1 from me, though I prefer the `??=` spelling to match the `??` operator
>> more closely.
>>
>> --
>> Brent Royal-Gordon
>> Architechies
>>
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>>
>
>
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>


-- 
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