toll-free bridged objects, retain and release

Question

I'm currently looking at a NSMutableSet created by the function CFSetCreateMutable(). The documentation states that the return value of CFSetCreateMutable() is toll-free bridged, meaning that I can simply cast it into a NSMutableSet. Does this mean that sending it the release message is perfectly valid? Am I always safe to assume that I can always treat such objects as if they were alloc'ed via an NS-class?

Answer 1

Just imagine that CFSetCreateMutable() is equivalent to [[NSMutableSet alloc] init] in that you have to release the object after you are done with it. If you are using ARC, you can cast a CFMutableSet to an NSMutableSet using a bridged cast: (__bridge_transfer NSMutableSet *)theCFSet. This will tell ARC that it is responsible for releasing the set after it goes out of scope.

Answer 2

The documentation states that the return value of CFSetCreateMutable() is toll-free bridged, meaning that I can simply cast it into a NSMutableSet. Does this mean that sending it the release message is perfectly valid?

Yes. This is explicitly guaranteed in the docs:

Note from the example that the memory management functions and methods are also interchangeable—you can use CFRelease with a Cocoa object and release and autorelease with a Core Foundation object.

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Am I always safe to assume that I can always treat such objects as if they were alloc'ed via an NS-class?

Not really: Currently, anything that exists in common between CFType and NSObject, such as -description/CFCopyDescription, works regardless of how you created the object, but they're not all explicitly guaranteed to work like the memory-management messages are.