[swift-evolution] Add something like [unowned self] syntax for passing instance methods into closure parameters without creating retain cycles

[Jordan Rose]

Unowned pointers aren't dangling in debug builds; they're more like zombie-detection, where you get a deterministic trap if you access them after the original instance is strong-released for the last time. I can't remember if this is enabled in release builds as well; under -Ounchecked they do become unsafe-unretained.

Jordan


> On Sep 14, 2016, at 10:51, Callionica (Swift) via swift-evolution <swift-evolution at swift.org> wrote:
> 
> How do you figure unowned pointers help you detect errors? Dangling pointers give you no guarantees.
> 
> On Wednesday, September 14, 2016, Karl Wagner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Sorry to hijack the thread, but I was working to fix the fact that we can't have optional unowned pointers in swift and Jordan said he didn't think anybody ever asked for it before. It made me worry about the kind of practices swift is encouraging.
> 
> The overhead of using weak pointers isn't massive, but it involves locking and updating global tables (http://stackoverflow.com/questions/23689155/lots-of-overhead-for-weak-property <http://stackoverflow.com/questions/23689155/lots-of-overhead-for-weak-property>). Unowned pointers don't have this overhead, and can also help you detect errors because they are fail-deadly.
> 
> But yeah, I'd like to be able to reference non-owning instance methods.
> 
> This <https://itunes.apple.com/app/apple-store/id922793622?pt=814382&mt=8&ct=how_i_email> is how I Email now
> 
> 
>> On Sep 14, 2016 at 7:45 am, <Rick Mann <javascript:_e(%7B%7D,'cvml','rmann at latencyzero.com');>> wrote:
>> 
>> 
>> > On Sep 13, 2016, at 22:34 , Xiaodi Wu via swift-evolution <swift-evolution at swift.org <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>> wrote:
>> 
>> >  
>> 
>> > It's similar to Linus' argument against using kernel debuggers (https://lwn.net/2000/0914/a/lt-debugger.php3 <https://lwn.net/2000/0914/a/lt-debugger.php3>). Understanding your code at a level above the source, and being careful, make you a better developer. There are no features in swift which compensate for a lack of understanding about how your code works.
>> 
>> 
>> 
>> Get off my lawn!
>> 
>> 
>> 
>> 
>> 
>> --  
>> 
>> Rick Mann
>> 
>> rmann at latencyzero.com <javascript:_e(%7B%7D,'cvml','rmann at latencyzero.com');>
>> 
>> 
>> 
>> 
>> 
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