Question

I’ve got a doubt about using “CFStringRef”. I’ve seen several examples of managing iPhone contacts and in most of them they use:

...
ABMultiValueRef emails = ABRecordCopyValue(person, kABPersonEmailProperty);
CFStringRef emailRef = ABMultiValueCopyValueAtIndex(emails, 0);
...
NSString *email = (NSString *)emailRef;

I don’t know why CFStringRef is used instead of using casting:

...
ABMultiValueRef emails = ABRecordCopyValue(person, kABPersonEmailProperty);
NSString *email = (NSString *)ABMultiValueCopyValueAtIndex(emails, 0);
...

Is it conventional to use CFStringRef? Is it correct to use direct casting?

Answer 1

CFString is “toll-free bridged” with its Cocoa Foundation counterpart,
NSString. This means that the Core Foundation type is interchangeable
in function or method calls with the bridged Foundation object.
Therefore, in a method where you see an NSString * parameter, you can
pass in a CFStringRef, and in a function where you see a CFStringRef
parameter, you can pass in an NSString instance. This also applies to
concrete subclasses of NSString.

Both are same.