<html><body><p>Currently on Linux, the various libdispatch types (dispatch_object_t, dispatch_queue_t, etc.) are imported into Swift as COpaquePointer on Linux. This causes a number of problems including:<br> (a) The intended subtyping relationships are lost, resulting in some of the dispatch APIs not being usable (<a href="https://bugs.swift.org/browse/SR-737">https://bugs.swift.org/browse/SR-737</a>)<br> (b) The libdispatch types can't be used in Swift where AnyObject is expected (<a href="https://bugs.swift.org/browse/SR-740">https://bugs.swift.org/browse/SR-740</a>)<br> (c) In Swift code that manipulates values coming from libdispatch, the expected retain/release operations are not generated by the compiler on Linux.<br><br>I can see two obvious ways to tackle these issues (and perhaps other problems with the same root cause I haven't encountered yet). <br> (1) Stay with the current C-level code of libdispatch where dispatch_object_t et al. simulate enough of the Objective-C object model that they can masquerade as Objective-C objects. Convince the Swift compiler to import them as Objective-C types on Linux even though there is not an Objective-C runtime (just the stubbed out bits of it that are in libdispatch).<br> (2) Change the current C-level code of libdispatch so that on Linux dispatch_object_t et al. simulate/implement enough of the Swift object model that they can masquerade as Swift objects. Convince the Swift compiler to import them as Swift types.<br><br>My gut is that (2) is the more desirable path to pursue. The main downside I see is that it will likely make libdispatch.so dependent on libswiftCore.so (to avoid replicating object model implementation functions). <br><br>Before seriously starting down either path, I'd like to get some guidance on what experts think the desired outcome should be and if I've overlooked a better option.<br><br>thanks,<br><br>--dave<br><BR>
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