I really like this idea. Spatially moving cleanup next to unsafe operations is
good practice.
In normal code, I want my cleanup to follow as closely as possible to my unsafe
act:
let buffer: UnsafeMutablePointer<CChar> =
UnsafeMutablePointer(allocatingCapacity: chunkSize)
defer { buffer.deallocateCapacity(chunkSize) }
(Sorry for the horrible example, but it's the best I could grep up with on a
moment's notice)
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
self.ptr = UnsafeMutablePointer<T>(allocatingCapacity: count)
deferringDeInit { self.ptr.deallocateCapacity(count) }
Or something.
-- E
p.s. Normally I put them on the same line with a semicolon but dang these
things can be long
> On Jun 8, 2016, at 10:54 AM, Graham Perks via swift-evolution
> <[email protected]> wrote:
>
> Teach init a 'defer'-like ability to deinit
>
> '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.
>
> Swift offers no support for resources acquired during 'init'.
>
> For an example, from
> https://www.mikeash.com/pyblog/friday-qa-2015-04-17-lets-build-swiftarray.html
>
> <https://www.mikeash.com/pyblog/friday-qa-2015-04-17-lets-build-swiftarray.html>
>
> init(count: Int = 0, ptr: UnsafeMutablePointer<T> = nil) {
> self.count = count
> self.space = count
>
> self.ptr = UnsafeMutablePointer<T>.alloc(count)
> self.ptr.initializeFrom(ptr, count: count)
> }
>
> deinit {
> ptr.destroy(...)
> ptr.dealloc(...)
> }
>
> 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).
>
> Changing the above code to use a 'defer' style deinit block might look like:
>
> init(count: Int = 0, ptr: UnsafeMutablePointer<T> = nil) {
> self.count = count
> self.space = count
>
> self.ptr = UnsafeMutablePointer<T>.alloc(count)
> self.ptr.initializeFrom(ptr, count: count)
>
> deinit {
> ptr.destroy(...)
> ptr.dealloc(...)
> }
>
> // NSNotificationCenter example too
> NSNotificationCenter.defaultCenter().addObserver(...)
> deinit {
> NSNotificationCenter.defaultCenter().removeObserver(...)
> }
> }
>
> 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.
>
> Considerations:
> 1. Should deinit blocks be invoked before or after code in an explicit deinit
> method?
> 2. Should deinit blocks be allowed in other methods; e.g. viewDidLoad()?
> 3. How should deinit blocks be prevented from strongly capturing self (thus
> preventing themselves from ever running!)?
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