Intro to ObjC Blocks

Blocks: a brief introduction to what they are and why you want to use them.

Slides are from a talk given for the Toronto Apple user group, July 2011.

1. OBJC BLOCKS Blocks, blocks, blocks!
2. WHO AM I? @gregheo Programmer, general nerd, on-call emergency presenter
3. USER EXPECTATIONS Performance, performance, performance! Fast startup Responsiveness Background processing
4. BLOCKS Part of the performance puzzle Modular Re-use GCD integration
5. BLOCKS Similar to: Closures Lambdas Anonymous functions
6. HELLO, WORLD ^{ NSLog(@"Hello, world!"); }; ^{ NSLog(@"Hello, world!"); }(); direct call!
7. HELLO, WORLD void (^myBlock)() = ^{ NSLog(@"Hello, world!"); }; myBlock();
8. SYNTAX int (*)(char); int (^)(NSString *); Function pointers, anyone?
9. THE STORY Some uses: Enumeration Map / reduce
10. CLASSIC METHODS Iterating over a collection: for loop? NSEnumerator?
11. MODERN METHOD NSArray *collection = [[NSArray alloc] ...]; for (id object in collection) { // do something here } Fast enumeration
12. BLOCK METHOD [myArray enumerateObjectsUsingBlock: ^(id obj, NSUInteger idx, BOOL *stop) { // do something }]; Inline block
13. BLOCK METHOD void (^myBlock)(id, NSUInteger, BOOL *) = ^(id obj, NSUInteger idx, BOOL *stop) { // do something }; [myArray enumerateObjectsUsingBlock:myBlock]; Pre-declared block
14. BLOCK METHOD void (^myBlock)(id, NSUInteger, BOOL *) = ^(id obj, NSUInteger idx, BOOL *stop) { // do something }; [myArray enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:myBlock]; Concurrency!
15. BENCHMARKS Regular enumeration 3.5 seconds Block enumeration 5 seconds Concurrent block 2.5 seconds (millions of iterations on an iPad 2)
16. NO FREE LUNCH Blocks are not a cure-all! Variable closure alloc/init overhead Memory allocation considerations
17. FURTHER TOPICS NSOperation NSBlockOperation Grand Central Dispatch
18. Questions? Comments? Rebuttals? ^{ return; }();