> On 01 May 2017, at 16:59, Dennis Weissmann <[email protected]> wrote:
>
>>
>> On May 1, 2017, at 4:46 PM, Rien via swift-users <[email protected]>
>> wrote:
>>
>> In my code I use a lot of queues. And (very often) I will use [weak self] to
>> prevent doing things when ‘self’ is no longer available.
>>
>> Now I am wondering: how does the compiler know that [weak self] is
>> referenced?
>>
>> I am assuming it keeps a reverse reference from self to the [weak self] in
>> order to ‘nil’ the [weak self] when self is nilled.
>>
>> But when a job is executing it has no control over the exclusive rights to
>> [weak self].
>>
>> I.e. [weak self] may be nilled by an outside event in the middle of say:
>>
>> if self != nil { return self!.myparam }
>>
>> The if finding [weak self] non nil, but the return finding [weak self] as nil
>>
>> Is that correct? i.e. should we never use the above if construct but always:
>>
>> return self?.myparam ?? 42
>>
>
> Yes, as you said, you never know when self will be nilled out, that's why you
> need to create a (temporary) strong reference to it, work on it, and when the
> block returns, your strong reference is released and self either goes away
> immediately (incase it was released elsewhere after the local binding to a
> strong variable and no other objects had a strong reference to it) or it will
> stay as long as no other object holds a strong reference to it.
>
> When the closure is more involved than a view lines, I often do a guard let
> `self` = self else { return } to conveniently work with a strong self inside
> the rest of the closure.
I was aware of that practise (use it myself) but I was not sure if it would
always work.
I.e. I have not found it documented that
let strongSelf = self
will actually retain ‘self’ an not create a strong reference to an intermediate
reference to self.
It makes sense though, otherwise there would be massive failures ‘out there’.
;-)
Thanks,
Rien.
>
>> Regards,
>> Rien
>>
>> Site: http://balancingrock.nl
>> Blog: http://swiftrien.blogspot.com
>> Github: http://github.com/Balancingrock
>> Project: http://swiftfire.nl - A server for websites build in Swift
>>
>>
>>
>>
>>
>>
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>
> - Dennis
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