Yeah, okay. So: how do I do this in a way that is safe? -- Rick Mann rm...@latencyzero.com
> On Apr 27, 2017, at 23:00, Rien <r...@balancingrock.nl> wrote: > > To address your question: > > https://developer.apple.com/reference/foundation/data/1779823-withunsafemutablebytes > > "Warning > The byte pointer argument should not be stored and used outside of the > lifetime of the call to the closure." > > Which is exactly what you are doing, hence the code is unsafe (no pun > intended). > > Regards, > Rien > > Site: http://balancingrock.nl > Blog: http://swiftrien.blogspot.com > Github: http://github.com/Balancingrock > Project: http://swiftfire.nl - A server for websites build in Swift > > > > > > >> On 28 Apr 2017, at 01:38, Rick Mann <rm...@latencyzero.com> wrote: >> >> >>> On Apr 27, 2017, at 01:48 , Alex Blewitt <alb...@apple.com> wrote: >>> >> ... >> >>> The let constant may not even be stored in a single place; if it's known to >>> be constant it can be in-lined at the point of use and potentially unpacked >>> and dead code elimination throw away the unused members, for example. >>> >>> If you want to pass in a let constant into the pointer, you can create a >>> copy of it locally in a local variable and then use that instead. However >>> this will be in the local scope, so the pointer isn't valid after it >>> returns. >> >> Ah, so this brings up another issue, then. Many of the calls in the C >> library take a pointer to some memory and hang on to it, filling it in at a >> later point (they make network requests). I've been doing it like this, and >> it's been working, but I wonder if this is fragile: >> >> class >> MyClass >> { >> func >> execute() >> { >> self.dataBuffer = Data(count: kLGSImageDataSize) >> precondition(self.dataBuffer != nil, "Unable to allocate image buffer >> (\(kLGSImageDataSize) bytes)") >> >> var params = c_library_params_t() >> params.data_capacity = self.dataBuffer!.count >> >> self.dataBuffer?.withUnsafeMutableBytes >> { (inBuffer) -> Void in >> // This call returns immediately, but assumes >> // it can write to inBuffer later… >> >> self.request = c_library_call(¶ms, inBuffer) >> } >> >> if self.request == nil >> { >> // Error >> } >> } >> >> var dataBuffer: Data? >> } >> >> >> -- >> Rick Mann >> rm...@latencyzero.com >> >> > _______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
