<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">I really love this idea. My mental model of it is that it is exactly like ‘defer’, except it works on the lifetime of the object instance instead of a function/method. Same thing, different scope.</div><div class=""><br class=""></div><div class="">I like how the creation and destruction are right next to one another. It also solves a lot of potential issues with partial initialization, I believe.</div><div class=""><br class=""></div><div class="">I might spell it ‘deferToDeinit’ or 'deferUntilDeinit'</div><div class=""><br class=""></div><div class="">The only issue I see is accidentally capturing self strongly. Is there a way to mark a closure as implicitly unowned self so the end programmer doesn’t have to worry about it?</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Jon</div><div class=""><blockquote type="cite" class=""><pre style="white-space: pre-wrap; background-color: rgb(255, 255, 255);" class="">Twitter tl;dr:
><i class=""> Brent: So each instance must remember which init was used for it and then run the matching deinit code at deinit time?
</i>><i class=""> Me: In my version, the constructive act and destructive act are always paired, even redundantly, using a stack if needed
</i>><i class=""> Graham: so all your deferredDeinit blocks would run, no matter which init was invoked?
</i>><i class=""> Brent: Closure stack in the worst case. Might be able to optimize to something cheaper if no captures. Degenerate case: `for i in 0..<10 { deinit { print(i) }
</i>
So continuing on from Twitter, assuming the compiler cannot optimize in the case of multiple inits, and init-redirections, how about allowing traditional deinit as well, and introduce compile-time optimization into traditional de-init if the compiler finds only one initialization path per class? We can also warn anyone using my version in a complicated degenerate way that it can be costly through education, manual, etc. It would also help if (especially in Cocoa), you could legally use shared initialization setup closures.
If I create an observer, I want to be able to handle its end-of-life at that point. If I allocate memory, ditto. Etc etc. Surely Swift should be able to support doing this.
-- E
><i class=""> On Jun 8, 2016, at 3:43 PM, Erica Sadun via swift-evolution <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">swift-evolution at swift.org</a>> wrote:
</i>><i class="">
</i>><i class=""> I really like this idea. Spatially moving cleanup next to unsafe operations is good practice.
</i>><i class="">
</i>><i class=""> In normal code, I want my cleanup to follow as closely as possible to my unsafe act:
</i>><i class="">
</i>><i class=""> let buffer: UnsafeMutablePointer<CChar> = UnsafeMutablePointer(allocatingCapacity: chunkSize)
</i>><i class=""> defer { buffer.deallocateCapacity(chunkSize) }
</i>><i class="">
</i>><i class=""> (Sorry for the horrible example, but it's the best I could grep up with on a moment's notice)
</i>><i class="">
</i>><i class=""> I like your idea but what I want to see is not the deinit child closure in init you propose but a new keyword that means defer-on-deinit-cleanup
</i>><i class="">
</i>><i class=""> self.ptr = UnsafeMutablePointer<T>(allocatingCapacity: count)
</i>><i class=""> deferringDeInit { self.ptr.deallocateCapacity(count) }
</i>><i class="">
</i>><i class=""> Or something.
</i>><i class="">
</i>><i class=""> -- E
</i>><i class=""> p.s. Normally I put them on the same line with a semicolon but dang these things can be long
</i>><i class="">
</i>>><i class=""> On Jun 8, 2016, at 10:54 AM, Graham Perks via swift-evolution <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">swift-evolution at swift.org</a> <mailto:<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">swift-evolution at swift.org</a>>> wrote:
</i>>><i class="">
</i>>><i class=""> Teach init a 'defer'-like ability to deinit
</i>>><i class="">
</i>>><i class=""> 'defer' is a great way to ensure some clean up code is run; it's declaritive locality to the resource acquisition is a boon to clarity.
</i>>><i class="">
</i>>><i class=""> Swift offers no support for resources acquired during 'init'.
</i>>><i class="">
</i>>><i class=""> For an example, from <a href="https://www.mikeash.com/pyblog/friday-qa-2015-04-17-lets-build-swiftarray.html" class="">https://www.mikeash.com/pyblog/friday-qa-2015-04-17-lets-build-swiftarray.html</a> <<a href="https://www.mikeash.com/pyblog/friday-qa-2015-04-17-lets-build-swiftarray.html" class="">https://www.mikeash.com/pyblog/friday-qa-2015-04-17-lets-build-swiftarray.html</a>>
</i>>><i class="">
</i>>><i class=""> init(count: Int = 0, ptr: UnsafeMutablePointer<T> = nil) {
</i>>><i class=""> self.count = count
</i>>><i class=""> self.space = count
</i>>><i class="">
</i>>><i class=""> self.ptr = UnsafeMutablePointer<T>.alloc(count)
</i>>><i class=""> self.ptr.initializeFrom(ptr, count: count)
</i>>><i class=""> }
</i>>><i class="">
</i>>><i class=""> deinit {
</i>>><i class=""> ptr.destroy(...)
</i>>><i class=""> ptr.dealloc(...)
</i>>><i class=""> }
</i>>><i class="">
</i>>><i class=""> Another 'resource' might be adding an NSNotificationCenter observer, and wanting to unobserve in deinit (no need in OS X 10.11, iOS 9, but for earlier releases this is a valid example).
</i>>><i class="">
</i>>><i class=""> Changing the above code to use a 'defer' style deinit block might look like:
</i>>><i class="">
</i>>><i class=""> init(count: Int = 0, ptr: UnsafeMutablePointer<T> = nil) {
</i>>><i class=""> self.count = count
</i>>><i class=""> self.space = count
</i>>><i class="">
</i>>><i class=""> self.ptr = UnsafeMutablePointer<T>.alloc(count)
</i>>><i class=""> self.ptr.initializeFrom(ptr, count: count)
</i>>><i class="">
</i>>><i class=""> deinit {
</i>>><i class=""> ptr.destroy(...)
</i>>><i class=""> ptr.dealloc(...)
</i>>><i class=""> }
</i>>><i class="">
</i>>><i class=""> // NSNotificationCenter example too
</i>>><i class=""> NSNotificationCenter.defaultCenter().addObserver(...)
</i>>><i class=""> deinit {
</i>>><i class=""> NSNotificationCenter.defaultCenter().removeObserver(...)
</i>>><i class=""> }
</i>>><i class=""> }
</i>>><i class="">
</i>>><i class=""> The need to provide a separate implemention of deinit is gone. Reasoning for 'defer' applies here. There is good locality between what was initialized and what needs cleaning up.
</i>>><i class="">
</i>>><i class=""> Considerations:
</i>>><i class=""> 1. Should deinit blocks be invoked before or after code in an explicit deinit method?
</i>>><i class=""> 2. Should deinit blocks be allowed in other methods; e.g. viewDidLoad()?
</i>>><i class=""> 3. How should deinit blocks be prevented from strongly capturing self (thus preventing themselves from ever running!)?
</i>><i class=""> </i></pre></blockquote><div class=""><br class=""></div></div></body></html>