ARC sure is great, isn't it? I don't miss littering my code with retain
, release
, and autorelease
.
Pretty much the only downside of ARC is that casting between toll-free bridging types (like CFStringRef
to NSString
and back) is a little more verbose. Before ARC, I wrote this:
NSString *stringObject = (NSString *)cfString;
CFStringRef cfString = (CFStringRef)stringObject;
After ARC, I have to write this:
NSString *stringObject = (__bridge NSString *)cfString;
CFStringRef cfString = (__bridge CFStringRef)stringObject;
Of course, there are some shortcuts. It's a little shorter to write this:
NSString *stringObject = (__bridge id)cfString;
CFStringRef cfString = (__bridge void *)stringObject; // or (__bridge CFTypeRef)stringObject
I could even define a couple of macros:
#define fromCF (__bridge id)
#define toCF (__bridge CFTypeRef)
NSString *stringObject = fromCF cfString;
CFStringRef cfString = toCF stringObject;
But using macros sometimes confuses Xcode's autocompletion mechanism. And with or without macros, using the generic types void *
, CFTypeRef
, and id
means giving up compiler type checking.
On the other hand, some non-toll-free-bridged types have handy conversions methods:
UIColor *uiColor = [UIColor colorWithCGColor:cgColor];
CGColorRef cgColor = uiColor.CGColor;
UIBezierPath *uiPath = [UIBezierPath bezierPathWithCGPath:cgPath];
CGPathRef cgPath = uiPath.CGPath;
UIImage *uiImage = [UIImage imageWithCGImage:cgImage];
CGImageRef cgImage = uiImage.CGImage;
There are probably others, but I happen to use those a lot.
Thanks to the magic of Objective-C categories, we can imbue the toll-free-bridged classes with convenience methods too. For example, we can trivially give NSString
a CFString
method:
@interface NSString (bridging)
@property (nonatomic, readonly) CFStringRef CFString;
@end
@implementation NSString (bridging)
- (CFStringRef)CFString {
return (__bridge CFStringRef)self;
}
@end
// Use it like this:
CFStringRef cfString = stringObject.CFString;
That's pretty nice. What about the other direction? We could follow the pattern of UIColor
and friends:
+ (NSString *)stringWithCFString:(CFStringRef)cfString {
return (__bridge NSString *)cfString;
}
// Use it like this:
NSString *stringObject = [NSString stringWithCFString:cfString];
But that's even more verbose than using __bridge
directly. Let's pick a shorter selector. How much shorter can we make it? Hold on to your britches, because the answer might surprise you:
+ (NSString *):(CFStringRef)cfString {
return (__bridge NSString *)cfString;
}
// Use it like this:
NSString *stringObject = [NSString:cfString];
Yes, you can have a selector that's nothing but a colon! It doesn't get any shorter than that. I think it's a pleasant combination of brevity and expressiveness, if a little exotic.
So, this little repository contains a bridging
category for each documented toll-free-bridged class in the Foundation framework. All of the categories are declared in one header file, BridgingCategories.h
, and defined in one source file, BridgingCategories.m
. These are the toll-free-bridged types:
CFArrayRef
/NSArray
CFAttributedStringRef
/NSAttributedString
CFCalendarRef
/NSCalendar
CFCharacterSetRef
/NSCharacterSet
CFDataRef
/NSData
CFDateRef
/NSDate
CFDictionaryRef
/NSDictionary
CFErrorRef
/NSError
CFLocaleRef
/NSLocale
CFMutableArrayRef
/NSMutableArray
CFMutableAttributedStringRef
/NSMutableAttributedString
CFMutableCharacterSetRef
/NSMutableCharacterSet
CFMutableDataRef
/NSMutableData
CFMutableDictionaryRef
/NSMutableDictionary
CFMutableSetRef
/NSMutableSet
CFMutableStringRef
/NSMutableString
CFNumberRef
/NSNumber
CFReadStreamRef
/NSInputStream
CFRunLoopTimerRef
/NSTimer
CFSetRef
/NSSet
CFStringRef
/NSString
CFTimeZoneRef
/NSTimeZone
CFURLRef
/NSURL
CFWriteStreamRef
/NSOutputStream
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The contents of this repository are dedicated to the public domain, in accordance with the CC0 1.0 Universal Public Domain Dedication, which is reproduced in the file COPYRIGHT
.