I've been playing around with a Swift wrapper for the FFmpeg C libraries (e.g., libavutil, libavcodec, libavformat, etc...). While providing some extensions to some of the core C structures I've run into something that doesn't feel quite right to me.
Before I provide a discussion here is a Gist [0] that I hope illustrates the problem. When inside of a Swift function declaration if I take `self` and send it to `withUnsafePointer` Swift requires the function to mark the function as `mutating`. This surprised me. Thanks to Swift being open source (🎉) I was able to go look at the implementation of `withUnsafePointer` [1]. And I'm no longer surprised that its required by the compiler; the definition marks the argument as `inout`. However, this seems wrong to me. In the "Pointers" section of "Using Swift with Cocoa and Objective-C (Swift 2.1)" [2] it says that `cost Type *` (pointer to a constant value) is equivalent to `UnsafePointer<Type>`. My understanding of C says that `const Type *` means that the instance of `Type` that the pointer points to cannot be modified. This corresponds with my understanding of the difference between `UnsafePointer<Type>` and `UnsafeMutablePointer<Type>`. Therefore, from my perspective I feel like there is a bug here. It also seems that marking the `arg` of `withUnsafePointer` to `var` instead of `inout` would allow it to compile and would more closely model the `UnsafePointer`. I'm still new to all this and I don't want to make a fool of myself. So I'd rather ask here before I move forward and file a bug and MR. [0] https://gist.github.com/RLovelett/e5ee7f173877bb8475dc [1] https://github.com/apple/swift/blob/8d9ef80304d7b36e13619ea50e6e76f3ec9221ba/stdlib/public/core/LifetimeManager.swift#L93-L102 [2] https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithCAPIs.html#//apple_ref/doc/uid/TP40014216-CH8-ID17 _______________________________________________ swift-dev mailing list swift-dev@swift.org https://lists.swift.org/mailman/listinfo/swift-dev
