Thank a lot Quinn, your solution to use inout works well without crashing. Question 1: - Also changing Helper to a class doesn’t seem to crash. Is that a solution that wouldn’t cause a crash or just works by chance ?
Background: Just a little background into what I was trying to achieve (I could be wrong): - I have a set of classes C1, C2, C3 which has a lot of common code - I would like to build something that can be reused without exposing the implementation details. (I can subclass but would expose the underlying functions, same applies to protocol as well) - I thought I would build helper class / struct which would contain the common code. I can make the helper a private property so that the functions wouldn’t be exposed to the instances of C1, C2, C3. In order to achieve that I had to pass some functions from C1 into the Helper struct. Question 2: - Is this problem (hiding implementation details) normally tackled using Helper class (or struct) or is there a more better approach ? Thanks and regards, Muthu > On 24 Jul 2017, at 4:14 PM, Quinn The Eskimo! via swift-users > <swift-users@swift.org> wrote: > > > On 24 Jul 2017, at 07:04, somu subscribe via swift-users > <swift-users@swift.org> wrote: > >> - Is there a bug in my code which is being detected in Xcode 9 ? > > Yes. The problem here is that `doSomething(f1:)` is a mutating function, so > it acts like it takes an `inout` reference to `self.helper`. That’s one > mutable reference. It then calls `Car.f1()`, which tries to get a > non-mutating reference to exactly the same struct. This is outlawed in Swift > 4 as part of the memory ownership effort. > > You can read more about the specific change in SE-0176 “Enforce Exclusive > Access to Memory”. > > <https://github.com/apple/swift-evolution/blob/master/proposals/0176-enforce-exclusive-access-to-memory.md> > > And the general background to this in the “Ownership Manifesto" > > <https://github.com/apple/swift/blob/master/docs/OwnershipManifesto.md> > >> If so could you please explain and suggest an alternate approach / fix ? > > It’s hard to offer concrete suggestions without knowing more about your > high-level goals. One option is for `doSomething(f1:)` to pass the `inout` > reference through to `f1`. For example: > > mutating func doSomething(f1: (inout Helper) -> ()) { > f1(&self) > } > > func f1(h: inout Helper) { > _ = h.v1 // no crash > } > > but whether that makes sense in your code is for you to decide. > > Share and Enjoy > -- > Quinn "The Eskimo!" <http://www.apple.com/developer/> > Apple Developer Relations, Developer Technical Support, Core OS/Hardware > > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users
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