[swift-evolution] Optional Setting

[James Campbell]

On second thoughts, I'm preparing one :)

On Wed, Dec 16, 2015 at 12:24 AM, James Campbell <james at supmenow.com> wrote:

> 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
>>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>  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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>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>
>>>
>>>
>>
>
>
> --
>  Wizard
> james at supmenow.com
> +44 7523 279 698
>



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