Thread-safe Singletons in Modern Objective-C

EVCSomeClass.m

@implementation EVCSomeClass

+(EVCSomeClass *)shared {
  static EVCSomeClass *shared = nil;
  
  // dispatch_once_t is typedef'd to a long
  static dispatch_once_t pred;
  
  // this block is executed synchronously, and only one time ever for the given predicate
  dispatch_once(&pred, ^{
    shared = [EVCSomeClass new];
  });
  
  return shared;
}

@end