ARC and bridged cast

I found another explanation in the iOS documentation that I think is easier to understand:

• __bridge transfers a pointer between Objective-C and Core Foundation with no transfer of ownership.

• __bridge_retained (CFBridgingRetain) casts an Objective-C pointer to a Core Foundation pointer and also transfers ownership to you.

  You are responsible for calling CFRelease or a related function to relinquish ownership of the object.

• __bridge_transfer (CFBridgingRelease) moves a non-Objective-C pointer to Objective-C and also transfers ownership to ARC.

  ARC is responsible for relinquishing ownership of the object.

Source: Toll-Free Bridged Types

I agree that the description is confusing. Since I just grasped them, I'll try to summarize:

• (__bridge_transfer <NSType>) op or alternatively CFBridgingRelease(op) is used to consume a retain-count of a CFTypeRef while transferring it over to ARC. This could also be represented by id someObj = (__bridge <NSType>) op; CFRelease(op);

• (__bridge_retained <CFType>) op or alternatively CFBridgingRetain(op) is used to hand an NSObject over to CF-land while giving it a +1 retain count. You should handle a CFTypeRef you create this way the same as you would handle a result of CFStringCreateCopy(). This could also be represented by CFRetain((__bridge CFType)op); CFTypeRef someTypeRef = (__bridge CFType)op;

• __bridge just casts between pointer-land and Objective-C object-land. If you have no inclination to use the conversions above, use this one.

Maybe this is helpful. Myself, I prefer the CFBridging… macros quite a bit over the plain casts.