Toll-Free Bridging

There are a number of data types in the Core Foundation framework and the Foundation framework that can be used interchangeably. This capability, called toll-free bridging, means that you can use the same data type as the parameter to a Core Foundation function call or as the receiver of an Objective-C message. For example, NSLocale (see NSLocale Class Reference) is interchangeable with its Core Foundation counterpart, CFLocale (see CFLocale Reference). Therefore, in a method where you see an NSLocale * parameter, you can pass a CFLocaleRef, and in a function where you see a CFLocaleRef parameter, you can pass an NSLocale instance. You cast one type to the other to suppress compiler warnings, as illustrated in the following example.

NSLocale *gbNSLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"];
CFLocaleRef gbCFLocale = (CFLocaleRef) gbNSLocale;
CFStringRef cfIdentifier = CFLocaleGetIdentifier (gbCFLocale);
NSLog(@"cfIdentifier: %@", (NSString *)cfIdentifier);
// logs: "cfIdentifier: en_GB"
CFRelease((CFLocaleRef) gbNSLocale);
 
CFLocaleRef myCFLocale = CFLocaleCopyCurrent();
NSLocale * myNSLocale = (NSLocale *) myCFLocale;
[myNSLocale autorelease];
NSString *nsIdentifier = [myNSLocale localeIdentifier];
CFShow((CFStringRef) [@"nsIdentifier: " stringByAppendingString:nsIdentifier]);
// logs identifier for current locale

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.

Toll-free bridging has been available since OS X v10.0. Table 13-1 provides a list of the data types that are interchangeable between Core Foundation and Foundation. For each pair, the table also lists the version of OS X in which toll-free bridging between them became available.

Table 13-1  Data types that can be used interchangeably between Core Foundation and Foundation

Core Foundation type

Foundation class

Availability

CFArrayRef

NSArray

OS X v10.0

CFAttributedStringRef

NSAttributedString

OS X v10.4

CFCalendarRef

NSCalendar

OS X v10.4

CFCharacterSetRef

NSCharacterSet

OS X v10.0

CFDataRef

NSData

OS X v10.0

CFDateRef

NSDate

OS X v10.0

CFDictionaryRef

NSDictionary

OS X v10.0

CFErrorRef

NSError

OS X v10.5

CFLocaleRef

NSLocale

OS X v10.4

CFMutableArrayRef

NSMutableArray

OS X v10.0

CFMutableAttributedStringRef

NSMutableAttributedString

OS X v10.4

CFMutableCharacterSetRef

NSMutableCharacterSet

OS X v10.0

CFMutableDataRef

NSMutableData

OS X v10.0

CFMutableDictionaryRef

NSMutableDictionary

OS X v10.0

CFMutableSetRef

NSMutableSet

OS X v10.0

CFMutableStringRef

NSMutableString

OS X v10.0

CFNumberRef

NSNumber

OS X v10.0

CFReadStreamRef

NSInputStream

OS X v10.0

CFRunLoopTimerRef

NSTimer

OS X v10.0

CFSetRef

NSSet

OS X v10.0

CFStringRef

NSString

OS X v10.0

CFTimeZoneRef

NSTimeZone

OS X v10.0

CFURLRef

NSURL

OS X v10.0

CFWriteStreamRef

NSOutputStream

OS X v10.0