[swift-evolution] A compiler option to warn if a closure captures a strong reference to a class instance?

Kenny Leung kenny_leung at pobox.com
Sat Feb 25 12:37:26 CST 2017

I’m back to writing Objective-C again, and it is actually warning you about possible reference cycles in your closures. I’m for Swift doing the same.


> On Feb 20, 2017, at 3:22 AM, Lauri Lehmijoki via swift-evolution <swift-evolution at swift.org> wrote:
> I'm developing an application where we use RxSwift heavily. RxSwift is a stream library. Consequently, closures that we pass to its combinators often live infinitely (this is because one can use RxSwift to represent infinitely long sequences in time). 
> Closures with infinite lifespan have implications for the question "what is the best reference capture mode for closures". My experience is that in RxSwift applications, the current default (strong) is almost always suboptimal. It leads to difficult-to-detect memory leaks and introduces a "gotcha" factor to programmers who are new to Swift. I'd prefer the default to be weak capture.
> So, I'd like to ask you two things:
> A) By default, why the Swift closure captures values strongly?
> B) Should we add a compiler option that, when turned on, would emit a warning if a closure strongly captures a class instance?
> Regards
> Lauri
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