Thanks a lot Zhao, using a serial queue works.
So both the solutions works, thanks.
> On 24 Jul 2017, at 5:39 PM, Zhao Xin via swift-users <swift-users@swift.org>
> wrote:
>
> You can use serial queue.
>
> class Car {
> var helper = Helper()
> lazy private var queue = DispatchQueue(label: "my queue")
>
> func test() {
> helper.doSomething(f1: f1)
> }
>
> func f1() {
> queue.async {
> _ = self.helper.v1 //Crash - Simultaneous accesses to <memory
> address>, but modification requires exclusive access.
> }
> }
> }
>
> Zhao Xin
>
> On Mon, Jul 24, 2017 at 4:22 PM, Quinn "The Eskimo!" via swift-users
> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote:
>
> On 24 Jul 2017, at 07:04, somu subscribe via swift-users
> <swift-users@swift.org <mailto: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
>
> <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
> <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/
> <http://www.apple.com/developer/>>
> Apple Developer Relations, Developer Technical Support, Core OS/Hardware
>
>
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