[swift-evolution] Optional Setting

[James Campbell]

Cool would be happy for you to do it :)  if you time, almost night here so
:) but happy for you to quote me in the proposal.



On Wed, Dec 16, 2015 at 12:17 AM, Jacob Bandes-Storch <jtbandes at gmail.com>
wrote:

> Would there be any caveats in introducing something like this, given the
> raciness of the operator? I guess it's not really a big deal — the other
> compound assignment operators (+=, -=, etc.) have the same problem.
>
> I'm not hearing much argument; sounds like many are in favor. I'd be happy
> to flesh out my radar into a "??=" proposal this evening, or someone else
> can do it if they'd like.
>
> Jacob
>
> On Tue, Dec 15, 2015 at 4:12 PM, Jordan Rose <jordan_rose at apple.com>
> wrote:
>
>> It's possible that @_transparent
>> <https://github.com/apple/swift/blob/master/docs/TransparentAttr.rst> 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
>>>>>>
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>>  Wizard
>>>> james at supmenow.com
>>>> +44 7523 279 698
>>>>
>>>
>>>
>>
>>
>> --
>>  Wizard
>> james at supmenow.com
>> +44 7523 279 698
>>  _______________________________________________
>> swift-evolution mailing list
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>>
>>
>>
>


-- 
 Wizard
james at supmenow.com
+44 7523 279 698
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