[swift-evolution] Should explicit `self.` be required when providing method as closure?

[Daniel Leping]

I'm not proposing syntax right now. Rather approach. Should we make ANY
capturing explicit? I don't know. Maybe someone has a stronger opinion here.

What I want to stress is this particular case with self autocapturing which
gives a headache to me a lot.

Any thoughts?


On Sun, 5 Mar 2017 at 18:42 Derrick Ho <wh1pch81n at gmail.com> wrote:

> [owned self] is weird. [self] is probably better and is currently the way
> to explicitly capture a variable.
>
> On Sun, Mar 5, 2017 at 6:35 AM Daniel Leping via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I think we can stretch it even further. Have an idea in mind.
>
> Automatically propagated self is actually a big issue. Most of the newbies
> do A LOT of mistakes with it. So I thought: what if we restrict it even
> further? Like have no access to self *unless* it's explicitly passed. It
> can be done the very same way we do with [weak self] or [unowned self]?
> What if we introduce [owned self] and remove automatic self propagation?
>
> This way one will have to at least think twice which propagation to choose
> instead of default strong reference which is not that good in many cases.
> Most for me, actually.
>
> If this idea gets any positive feedback and the issue is a headache not to
> me only I'll create a separate thread and/or proposal.
>
> On Sat, 4 Mar 2017 at 21:55 Kenny Leung via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Is callback an autoclosure, or just a regular argument?
>
> -Kenny
>
>
> On Mar 3, 2017, at 1:14 PM, Alex Johnson via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Hi list members,
>
> During code review today, I noticed a really subtle memory leak that
> looked like:
>
>     self.relatedObject = RelatedObject(callback: relatedObjectDidFinish)
>
> Where `relatedObject` is a strong reference, `callback` is an escaping
> closure, and `relatedObjectDidFinish` is a method of `self`. From a memory
> management perspective, this code is equivalent to:
>
>     self.relatedObject = RelatedObject(callback: {
> self.relatedObjectDidFinish })
>
> In the second example, an explicit `self.` is required. It’s my
> understanding that this is to highlight that the closure keeps a strong
> reference to `self`. But, when passing a method, there is no such
> requirement, which makes it easier to accidentally create a retain cycle.
>
> This made me wonder if an explicit `self.` should be required when passing
> a method as an escaping closure. And whether that would help in the same
> way that the explicit `self.` *inside* the closure is intended to.
>
> If it were required, the code in the first example would be:
>
>     self.relatedObject = RelatedObject(callback:
> self.relatedObjectDidFinish)
>
> What do you think?
>
> *Alex Johnson*
> ajohnson at walmartlabs.com
> ajohnson on Slack
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