Casting an NSError return to a CFErrorRef return

Question

I have a function that returns an NSError object by reference:

NSData *foo(NSData *foo, NSError *__autoreleasing *outError);

This function uses an API that takes a pointer to storage for a CFErrorRef. I'd like to just pass outError to the underlying function directly, but I can't figure out the correct combination of declaration keywords and cast keywords to make clang agree with that plan. Is there one?

Answer 1

If you look at the clang notes for __autoreleasing it mentions that the magic happens at assignment time, which means that automatic casting can't help here. You need to actually make the assignment using a temporary variable as mentioned in the comments on the original post.

Answer 2

Try this:

NSError+CFErrorRef.h

@interface NSError (CFErrorRef)

- (CFErrorRef) cferror;

@end

NSError+CFErrorRef.m

#import "NSError+CFErrorRef.h"

@implementation NSError (CFErrorRef)

- (CFErrorRef) cferror
{
    CFStringRef domain = (CFStringRef) self.domain;

    CFDictionaryRef userInfo = (__bridge CFDictionaryRef) self.userInfo;

    return CFErrorCreate(kCFAllocatorDefault, domain, self.code, userInfo);
}

@end

I wrote a quick little unit test to verify everything converted over and it appears to be working correctly. Then you can just perform the following selector on your NSError object

CFErrorRef e = [error cferror];