[swift-evolution] Optional Setting

[Matthew Johnson]

+1 on ??= for consistency with ??

Sent from my iPad

> On Dec 15, 2015, at 6:12 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
> 
> It's possible that @_transparent is handled early enough in the compiler that we actually would get this behavior. I'm not sure, though.
> 
> +1 from me whether or not didSet is always called, though. "a = a ?? b" always calls didSet anyway.
> 
> Jordan
> 
> P.S. There's nothing particularly useful in the Radar, except that together with the dups there are three suggested spellings: "=?", "?=", and "??=". My vote is with Brent for "??=".
> 
>> On Dec 15, 2015, at 15:26 , James Campbell via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> :) Wasn't expecting it to be trivial. but yeah if it could somehow be short circuited so didSet, willSet isn't called when there is a value already. that would be awesome.
>> 
>> Could the willSet, didSet behaviour  be tied to the = behaviour ?  in your example above the operation ultimately cascades into a = operation. 
>> 
>> Same with operations such as *= or /= ultimately it has to do a = operation to set the new calculated value.
>> 
>>> On Tue, Dec 15, 2015 at 11:23 PM, Jacob Bandes-Storch <jtbandes at gmail.com> wrote:
>>> I agree that would be nice. Just pointing out that it's nontrivial. If you implement this custom operator today, you get different behavior.
>>> 
>>> Jacob
>>> 
>>>> On Tue, Dec 15, 2015 at 3:21 PM, James Campbell <james at supmenow.com> wrote:
>>>> 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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>>>> 
>>>> 
>>>> -- 
>>>>  Wizard
>>>> james at supmenow.com
>>>> +44 7523 279 698
>> 
>> 
>> 
>> -- 
>>  Wizard
>> james at supmenow.com
>> +44 7523 279 698
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