[swift-evolution] [Proposal] Allow upgrading weak self to strong self by assignment

[Shawn Erickson]

Oops clicked send by mistake...

I wanted to ponder going one step farther (of course it means modifying the
language a little).

networkRequest.fetchData() { [weak self, weak foo] result in
    guard strong self else { ..., return }
    guard strong foo else { ..., return }
    ...
}

networkRequest.fetchData() { [weak self, weak foo] result in
    if strong self {... if strong foo {...} else {...} ...} else {...}
}

... using strong as an attempt to imply that after the guard I want self
(or foo, etc.) to be a strong reference or in the first part of the if I
want self to be strong.


On Fri, Feb 19, 2016 at 1:39 PM Shawn Erickson <shawnce at gmail.com> wrote:

> I also like this proposal. I wish we could go further in removing the
> boilerplate but then you have to start to consider usage scenarios that you
> would lose in the process.
>
> For example [guard self] capture option supports one specific situation
> without the ability of the block to take alternate actions in the situation
> of weak self being nil and also requiring no return blocks. This is great
> obviously for that particular situation however it doesn't really help with
> the other situations.
>
> This proposal allows for a wide range of possibilities in a language
> natural way while reducing the code gyrations we currently do.
>
>
> On Fri, Feb 19, 2016 at 12:21 PM Taras Zakharko via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Very much in favor of this solution (removing the standalone let self =
>> self!). Its does not introduce any new syntax, its semantics is very
>> obvious, its explicit, and its also much more flexible than the alternative
>> guard capture list proposal while keeping magic to the necessary minimum.
>>
>> — Taras
>>
>>
>> On 19 Feb 2016, at 20:40, Evan Maloney via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> On Feb 19, 2016, at 2:30 PM, plx via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> networkRequest.fetchData() { [weak self] result in
>>     guard self != nil else { return }
>>
>>     let self = self!
>>
>> …isn’t there a race condition in this example (admittedly an *unlikely*
>> one in most settings, but still…)?
>>
>>
>> Yes, that's a good point.
>>
>> Now that I think about it, allowing a standalone `let self =` could never
>> be implemented in a way *guaranteed* to avoid a race condition, so perhaps
>> I should remove it from the proposal altogether.
>>
>> When I incorporate the next round of feedback, I'll rework the proposal
>> to indicate that it can only be used with `if let` or `guard let`.
>>
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