Bridge casts for collection elements - ios

Question

I'm using a vendor API that returns a CFDictionaryRef that can contain a variety of CF object types and which the caller needs to CFRelease. I'd like to cast it to an NSDictionary to more easily work with it, and want to make sure I understand I'm handling the elements correctly in terms of casting.
It looks to me like toll-free bridged types (e.g. CFString, CFNumber) are just handled by NSDictionary and I can just get the NS types as I would if they'd been Obj-C types all along (I'm guessing there's a bridge cast going on under the covers).
For a non-toll-free bridged type (e.g. CFHost) it looks like I can bridge cast the result from -valueForKey: into the CF type and go from there, though I'm not positive if I need to release that value or not.
Here's some sample code that illustrates the problem. Is this the right way to handle things?
// Caller is responsible for releasing returned value
//
+ (CFDictionaryRef)someCFCreateFunctionFromVendor
{
CFMutableDictionaryRef cfdict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
CFDictionarySetValue(cfdict, CFSTR("string1"), CFSTR("value"));
int i = 42;
CFDictionarySetValue(cfdict, CFSTR("int1"), CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &i));
CFHostRef host = CFHostCreateWithName(kCFAllocatorDefault, CFSTR("myhost"));
CFDictionarySetValue(cfdict, CFSTR("host1"), host);
return cfdict;
}
+ (void)myMethod
{
NSDictionary *dict = CFBridgingRelease([self someCFCreateFunctionFromVendor]);
for (NSString *key in [dict allKeys]) {
id value = [dict valueForKey:key];
NSLog(#"%# class: %#", key, [value class]);
if ([value isKindOfClass:[NSString class]]) {
NSString *str = (NSString *)value;
NSLog(#"%# is an NSString with value %#", key, str);
} else if ([value isKindOfClass:[NSNumber class]]) {
NSNumber *num = (NSNumber *)value;
NSLog(#"%# is an NSNumber with value %#", key, num);
} else if ([value isKindOfClass:[NSHost class]]) {
NSLog(#"%# is an NSHost", key); // never hit because no toll-free bridge to NSHost
} else {
NSLog(#"%# is an unexpected class", key);
}
// Sample handling of non-toll-free bridged type
if ([key isEqualToString:#"host1"]) {
CFHostRef host = (__bridge CFHostRef)value;
NSArray *names = (__bridge NSArray *)(CFHostGetNames(host, false));
NSLog(#"host1 names: %#", names);
// I don't think I need to CFRelease(host) because ARC is still handling value
}
}
}
Output...
string1 class: __NSCFConstantString
string1 is an NSString with value strvalue
int1 class: __NSCFNumber
int1 is an NSNumber with value 42
host1 class: __NSCFType
host1 is an unexpected class
host1 names: ( myhost )

Answer 1

Ironically, the only error in your code is in the Core Foundation, non-ARC stuff. Your +someCFCreateFunctionFromVendor method calls CFNumberCreate() and CFHostCreateWithName(), both of which are Create functions, but doesn't CFRelease() the objects after adding them to the dictionary. It should. Otherwise, it's a leak. The static analyzer would catch that, by the way. (For the CFNumber, that means you have to split creation into a separate line so you can reference the object after adding it to the dictionary.)
You must not release the host object in +myMethod because that code doesn't receive ownership of it. It has nothing to do with ARC. You wouldn't release it there in MRR (manual retain/release) code, either.