Sorry. If you are doing something on implementing proposals, you should use [swift-dev] list instead. Yes. I do don't know what the COW means.
Zhaoxin On Fri, Nov 18, 2016 at 11:09 PM, Adrian Zubarev < adrian.zuba...@devandartist.com> wrote: > I’m sorry but you seem not to understand what I’m asking for! > > If you don’t know what a mutable view is, please read this proposal to > get the basic idea: https://github.com/natecook1000/swift-evolution/ > blob/nc-dictionary-collections/proposals/0000-dictionary-key-and-value- > collections.md > > Your answer doesn’t make any sense. > > > > -- > Adrian Zubarev > Sent with Airmail > > Am 18. November 2016 um 16:05:25, Zhao Xin (owe...@gmail.com) schrieb: > > protocol Copyable { > > func copy() -> Self > > } > > > final class Storage:Copyable { > > > > var keys: [String] = [] > > var values: [Int] = [] > > > > func copy() -> Storage { > > let s = Storage() > > s.keys = keys > > s.values = values > > > > return s > > } > > } > > > public struct Document:Copyable { > > > > var _storageReference: Storage > > > > public init() { > > > > self._storageReference = Storage() > > } > > > > public init(_ values: DocumentValues) { > > > > self._storageReference = values._storageReference > > } > > > > public var values: DocumentValues { > > > > get { return DocumentValues(self) } > > > > set { self = Document(newValue) } > > } > > > > public func copy() -> Document { > > var d = Document() > > d._storageReference = _storageReference.copy() > > > > return d > > } > > } > > > var document = Document() > > > let copy = document.copy() > > > // just assume we already added some values and can mutate safely on a > given index > > // mutation in place > > document.values[0] = 10 // <--- this will only mutate `document` but not > `copy` > > > You use `class` property inside `struct`, so the `struct` is no longer > copyable. You have to do it yourself. > > > Zhaoxin > > On Fri, Nov 18, 2016 at 10:09 PM, Adrian Zubarev < > adrian.zuba...@devandartist.com> wrote: > >> Ups sorry for CCing the post to the evolution list. That happens from >> time to time. :/ >> >> >> -- >> Adrian Zubarev >> Sent with Airmail >> >> Am 18. November 2016 um 15:07:43, Adrian Zubarev ( >> adrian.zuba...@devandartist.com) schrieb: >> >> I apologize about the weak/unowned issue I mentioned. I kinda missed >> that portion from the docs Weak references do not affect the result of >> this function.. >> >> Okay it’s clear to me now why the result is evaluated as false. >> >> But how do I solve the COW problem for mutable views? >> >> >> -- >> Adrian Zubarev >> Sent with Airmail >> >> Am 18. November 2016 um 15:04:55, Adrian Zubarev ( >> adrian.zuba...@devandartist.com) schrieb: >> >> This doesn’t make any sense. >> >> Somewhere from the Swift book: >> >> Weak and unowned references enable one instance in a reference cycle to >> refer to the other instance *without keeping a strong hold on it*. The >> instances can then refer to each other without creating a strong reference >> cycle. >> >> From the sdlib of the function isKnownUniquelyReferenced: >> >> Returns a Boolean value indicating whether the given object is a class >> instance known to have *a single strong reference*. >> >> unowned doesn’t increase the reference count, so the view in the >> examples I showed should have no strong reference to that class instance. >> The only strong reference that exists is from Document. So why exactly >> is the result of the second isKnownUniquelyReferenced call false again? >> >> >> -- >> Adrian Zubarev >> Sent with Airmail >> >> Am 18. November 2016 um 14:50:57, Zhao Xin (owe...@gmail.com) schrieb: >> >> >Why is the second check false, even if the property is marked as unowned for >> the view? >> >> Please search the mailing list, this is not the first time it comes as a >> new question. Shortly speaking, it is `false` only because you used >> `unowned`. If you you can grantee it always exists. Just use it directly, >> this is what `unowned` for. If you can't grantee that. You should use >> `weak` and check it with `if let` or `if foo == nil` >> >> Zhaoxin >> >> >> On Fri, Nov 18, 2016 at 8:05 PM, Adrian Zubarev via swift-users < >> swift-users@swift.org> wrote: >> >>> Hi there, >>> >>> I just can’t get my head around mutable views and COW. >>> >>> Here is a small example: >>> >>> final class Storage { >>> >>> var keys: [String] = [] >>> var values: [Int] = [] >>> } >>> >>> public struct Document { >>> >>> var _storageReference: Storage >>> >>> public init() { >>> >>> self._storageReference = Storage() >>> } >>> >>> public init(_ values: DocumentValues) { >>> >>> self._storageReference = values._storageReference >>> } >>> >>> public var values: DocumentValues { >>> >>> get { return DocumentValues(self) } >>> >>> set { self = Document(newValue) } >>> } >>> } >>> >>> public struct DocumentValues : MutableCollection { >>> >>> unowned var _storageReference: Storage >>> >>> init(_ document: Document) { >>> >>> self._storageReference = document._storageReference >>> } >>> >>> public var startIndex: Int { >>> >>> return self._storageReference.keys.startIndex >>> } >>> >>> public var endIndex: Int { >>> >>> return self._storageReference.keys.endIndex >>> } >>> >>> public func index(after i: Int) -> Int { >>> >>> return self._storageReference.keys.index(after: i) >>> } >>> >>> public subscript(position: Int) -> Int { >>> >>> get { return _storageReference.values[position] } >>> >>> set { self._storageReference.values[position] = newValue } // That >>> will break COW >>> } >>> } >>> >>> First of all the _storageReference property is unowned because I wanted >>> to check the following: >>> >>> var document = Document() >>> >>> print(CFGetRetainCount(document._storageReference)) //=> 2 >>> print(isKnownUniquelyReferenced(&document._storageReference)) // true >>> >>> var values = document.values >>> >>> print(CFGetRetainCount(values._storageReference)) //=> 2 >>> print(isKnownUniquelyReferenced(&values._storageReference)) // false >>> >>> Why is the second check false, even if the property is marked as unowned >>> for the view? >>> >>> Next up, I don’t have an idea how to correctly COW optimize this view. >>> Assume the following scenario: >>> >>> Scenario A: >>> >>> var document = Document() >>> >>> // just assume we already added some values and can mutate safely on a >>> given index >>> // mutation in place >>> document.values[0] = 10 >>> >>> VS: >>> >>> Scenario B: >>> >>> var document = Document() >>> >>> let copy = document >>> >>> // just assume we already added some values and can mutate safely on a >>> given index >>> // mutation in place >>> document.values[0] = 10 // <--- this should only mutate `document` but not >>> `copy` >>> >>> We could change the subscript setter on the mutable view like this: >>> >>> set { >>> >>> if !isKnownUniquelyReferenced(&self._storageReference) { >>> >>> self._storageReference = ... // clone >>> } >>> self._storageReference.values[position] = newValue >>> } >>> >>> There is only one problem here. We’d end up cloning the storage every >>> time, because as shown in the very first example, even with unowned the >>> function isKnownUniquelyReferenced will return false for scenario A. >>> >>> Any suggestions? >>> >>> PS: In general I also wouldn’t want to use unowned because the view >>> should be able to outlive it’s parent. >>> >>> >>> -- >>> Adrian Zubarev >>> Sent with Airmail >>> >>> _______________________________________________ >>> swift-users mailing list >>> swift-users@swift.org >>> https://lists.swift.org/mailman/listinfo/swift-users >>> >>> >> >
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