Swift 2 CFType Conversion

Question

Created Aug ’15

Replies 6

Boosts 0

Participants 4

In Swift 1.2 I had a C function with the following signature:

__nonnull CFArrayRef FDCreateSupportedAudioFileExtensions() CF_RETURNS_RETAINED;

I know that this function returns an array of

CFStringRef

instances, so I called it from Swift like this:

let supportedAudioTypes = FDCreateSupportedAudioFileExtensions() as! [String]

and everything worked as expected. However, in Swift 2 this code fails at runtime due to the forced cast (

EXC_BAD_INSTRUCTION

). I'm able to get things working with the following:

let supportedAudioTypes = FDCreateSupportedAudioFileExtensions() as NSArray as! [String]

I'm unsure what changed from Swift 1.2 to 2.0. Is this a bug in the current version of Swift or have I missed something? Everything I've read implies that CFTypes are toll-free bridged to their Swift counterparts so I'm not sure why what used to work is now failing.

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Answer 1

SevenTenEleven OP

Aug ’15

I agree that it doesn't make sense for the first not to work but the second to work. If you haven't already, please file a bug report with your project attached.

One possibility is that in your first example you never actually imported Foundation. If you only use Core Foundation, Swift doesn't set up all of the same bridging infrastructure that it would otherwise.

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Answer 2

sbooth OP

Sep ’15

Thanks for the response. I filed bug 22593670 which includes a project recreating the problem. To answer your question about importing Foundation vs. CoreFoundation- I imported CoreFoundation only in my C wrapper. Importing Foundation from Swift didn't help the issue.

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Answer 3

lupinglade OP

Sep ’15

Same issue here causing many headaches and this breaks code that used optional binding: if let x = functionThatReturnsCFType() as? String {} now always fails Breaks code all over, silently!

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Answer 4

lupinglade OP

Sep ’15

Would be nice if someone from Apple could take a look at this as this looks to be a serious issue in Swift 2.0. CFType conversions, especially when used with optional return values are *extremely* broken.

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Answer 5

lupinglade OP

Sep ’15

Here's a simple example:

        let utis = UTTypeCreateAllIdentifiersForTag(kUTTagClassFilenameExtension, "mov", nil)?.takeRetainedValue()

How do we get a [String] out of this?? Nothing seems to work...

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Answer 6

OOPer OP

Sep ’15

You'd better read the original post carefully.

let utis = UTTypeCreateAllIdentifiersForTag(kUTTagClassFilenameExtension, "mov", nil)?.takeRetainedValue() as NSArray? as! [String]
print(utis[0]) //->com.apple.quicktime-movie

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