Oleg Andreev



Software designer from St. Petersburg living in Paris.

Author of Gitbox version control app.

Lead developer of FunGolf, golfer's personal assistant on iOS.

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August 6

Fixing modern Objective-C syntax with subscripting for iOS 5 and iOS 4

Xcode 4.4 is capable of subscript syntax and allows migrating the code from [arr objectAtIndex:0] to arr[0]. A few tweaks needed, however:

1. While OS X 10.8 SDK already contains objectAtIndexedSubscript: and objectForKeyedSubscript:, iOS 5.1 SDK does not. To make compiler happy, you should add this:


#if __IPHONE_OS_VERSION_MAX_ALLOWED < 60000
@interface NSDictionary(IGSubscripts)
- (id)objectForKeyedSubscript:(id)key;
@end

@interface NSMutableDictionary(IGSubscripts)
- (void)setObject:(id)obj forKeyedSubscript:(id )key;
@end

@interface NSArray(IGSubscripts)
- (id)objectAtIndexedSubscript:(NSUInteger)idx;
@end

@interface NSMutableArray(IGSubscripts)
- (void)setObject:(id)obj atIndexedSubscript:(NSUInteger)idx;
@end
#endif

2. To deploy new stuff back to iOS 5 and iOS 4, you need ARCLite. Somehow ARC itself works without extra configuration, but subscripting requires explicit linker flag:

In project settings add to Other Linker Flags: “-fobjc-arc”

3. If you use Edit -> Refactor -> Convert to Modern Objective-C Syntax, it will replace -[NSLocale objectForKey:] with a square brackets syntax, which is not supported by NSLocale. This is the only bug I have found with the automatic translation. NSCache and NSUserDefaults are not touched by the migrator.