[swift-evolution] Optional Setting

[James Campbell]

:) 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20151215/d1b58752/attachment.html>