OBJC BLOCKS Blocks, blocks, blocks! 

WHO AM I? @gregheo Programmer, general nerd, on-call emergency presenter 

USER EXPECTATIONS Performance, performance, performance! Fast startup Responsiveness Background processing 

BLOCKS Part of the performance puzzle Modular Re-use GCD integration 

BLOCKS Similar to: Closures Lambdas Anonymous functions 

HELLO, WORLD ^{ NSLog(@"Hello, world!"); }; ^{ NSLog(@"Hello, world!"); }(); direct call! 

HELLO, WORLD void (^myBlock)() = ^{ NSLog(@"Hello, world!"); }; myBlock(); 

SYNTAX int (*)(char); int (^)(NSString *); Function pointers, anyone? 

THE STORY Some uses: Enumeration Map / reduce 

CLASSIC METHODS Iterating over a collection: for loop? NSEnumerator? 

MODERN METHOD NSArray *collection = [[NSArray alloc] ...]; for (id object in collection) { // do something here } Fast enumeration 

BLOCK METHOD [myArray enumerateObjectsUsingBlock: ^(id obj, NSUInteger idx, BOOL *stop) { // do something }]; Inline block 

BLOCK METHOD void (^myBlock)(id, NSUInteger, BOOL *) = ^(id obj, NSUInteger idx, BOOL *stop) { // do something }; [myArray enumerateObjectsUsingBlock:myBlock]; Pre-declared block 

BLOCK METHOD void (^myBlock)(id, NSUInteger, BOOL *) = ^(id obj, NSUInteger idx, BOOL *stop) { // do something }; [myArray enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:myBlock]; Concurrency! 

BENCHMARKS Regular enumeration 3.5 seconds Block enumeration 5 seconds Concurrent block 2.5 seconds (millions of iterations on an iPad 2) 

NO FREE LUNCH Blocks are not a cure-all! Variable closure alloc/init overhead Memory allocation considerations 

FURTHER TOPICS NSOperation NSBlockOperation Grand Central Dispatch 

Questions? Comments? Rebuttals? ^{ return; }();