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

[Daniel Leping]

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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