Thanks! That’s a very elegant solution. /Daniel
> On 05 Jan 2016, at 20:48, Jacob Bandes-Storch <jtban...@gmail.com> wrote: > > This is what withExtendedLifetime is for: > https://developer.apple.com/library/ios/documentation/Swift/Reference/Swift_StandardLibrary_Functions/index.html#//apple_ref/swift/func/s:FSs20withExtendedLifetimeu0_rFzTq_Fzq_q0__q0_ > > On Tue, Jan 5, 2016 at 9:57 AM, Kristof Liliom via swift-users > <swift-users@swift.org> wrote: > Hi, > > I'm not a pro on Swift, but I would try to use the Unmanaged wrapper struct. > > Sample (might not be correct, didn't try) > > // Using Unmanaged > func dummyfunc(backingData: dispatch_data_t) { > var base = UnsafePointer<Void>() > var size = Int() > let mapped = dispatch_data_create_map(backingData, &base, &size) > > // New code > let unmanaged = Unmanaged.passUnretained(mapped) > defer { unmanaged.release() } > > let buffer = UnsafeBufferPointer<Void>(start: UnsafePointer<Void>(base), > count: size / sizeof(Void)) > return someFunction(buffer) > } > > Best Regards, > Chris > > > On 05 Jan 2016, at 16:57, Daniel Eggert via swift-users > > <swift-users@swift.org> wrote: > > > > How do I extend the lifetime of a variable, i.e. make sure that ARC is less > > aggressive? > > > > clang has an attribute called objc_precise_lifetime — does Swift have > > something similar? > > > > > > I have this code: > > > > do { > > var base = UnsafePointer<Void>() > > var size = Int() > > let mapped = dispatch_data_create_map(backingData, &base, &size) > > let buffer = UnsafeBufferPointer<A>(start: UnsafePointer<A>(base), > > count: size / sizeof(A)) > > return someFunction(buffer) > > } > > > > I need the ‘mapped’ variable to stay in scope (i.e. not be released) until > > the end of the scope, but ARC is free to release it immediately — in fact > > the compiler warns me that the immutable value is never used. > > > > But the API contract with dispatch_data_create_map(3) is that the values in > > ‘base’ and ‘size’ are only valid as long as ‘mapped’ is around. The above > > code is passing a buffer into ‘someFunction’ that’s no longer valid. > > > > How do I fix this? > > > > /Daniel > > > > _______________________________________________ > > swift-users mailing list > > swift-users@swift.org > > https://lists.swift.org/mailman/listinfo/swift-users > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users > _______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
