[swift-dev] isUniquelyReferenced issues

[Patrick Pijnappel]

The modified version doesn't seem to change any of the results (on -O or
-Onone). Note that the problem is that it's *not* uniquely referenced
inside bar where it actually should be – that would mean that ownership is
currently not directly transferred right?

On Fri, Apr 1, 2016 at 10:27 AM, Joe Groff <jgroff at apple.com> wrote:

>
> > On Mar 31, 2016, at 4:21 PM, Joe Groff via swift-dev <
> swift-dev at swift.org> wrote:
> >
> >>
> >> On Mar 31, 2016, at 3:58 PM, Patrick Pijnappel via swift-dev <
> swift-dev at swift.org> wrote:
> >>
> >> In trying to implement a COW type, but I'm running into problems with
> isUniqueReferenced breaking in even fairly simple cases. For example (with
> -O) the code below prints "bar: false", commenting out the print in test()
> makes it print "bar: true", and removing the var parameter var foo: Foo and
> using var foo = foo instead breaks it again. Am I doing something wrong
> here?
> >>
> >> class FooStorage { var x: Int = 0 }
> >>
> >> struct Foo { var storage = FooStorage() }
> >>
> >> func bar(var foo: Foo) {
> >>      print("bar: \(isUniquelyReferencedNonObjC(&foo.storage))")
> >> }
> >>
> >> func test() {
> >>      var foo = Foo()
> >>      print("test: \(isUniquelyReferencedNonObjC(&foo.storage))")
> >>      bar(foo)
> >> }
> >>
> >> test()
> >
> > You're not doing anything wrong, this is just the ARC optimizer at work.
> `foo` inside `test` is dead after the call to `bar`, so ownership is
> transferred directly to `bar`'s parameter.
>
> If you want to ensure that `foo` remains alive despite this, you can use
> `withExtendedLifetime`:
>
> class FooStorage { var x: Int = 0 }
>
> struct Foo { var storage = FooStorage() }
>
> func bar(var foo: Foo) {
>         print("bar: \(isUniquelyReferencedNonObjC(&foo.storage))")
> }
>
> func test() {
>         var foo = Foo()
>         print("test: \(isUniquelyReferencedNonObjC(&foo.storage))")
>         withExtendedLifetime(foo) {
>                 bar(foo)
>         }
> }
>
> -Joe
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-dev/attachments/20160401/adb56a87/attachment.html>