B0bcat

- (void)doSomething {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [queue addOperationWithBlock:^{
        // load data from disk
        NSLog(@"done");
    }];
}

B0bcat

class FileWriter {
  func writeDocument(text: String?, completion((Bool, NSError?) -> Void)?) -> NSError? {
       var error: NSError?
       if let cText = text {
           dispatch_async(myQueue) {() -> Void in 
               let error = writeAndSaveFile(cText)
               completion?((error == nil), error)
           }
       } else {
           error = NSError.dataEmptyError()

B0bcat

@interface MyTVC : UIViewController

@property (strong, nonatomic) NSMapTable switchesToIndexPaths;

@end

@implementation MyTVC

- (void)viewDidLoad {
	[super viewDidLoad];

B0bcat

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