Quickies for Blocks

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General

• Block Typedef [permalink]
  I can never remember the syntax for function pointer typedefs, and therefore can never remember the syntax for block typedefs:

  typedef CGRect (^GroovyBlock)(NSInteger spoon, NSString *waffle);

  Creates a typedef called GroovyBlock that returns a CGRect and takes an integer and a string.

• Block syntax for properties [permalink]
  Want to have a block as a @property? This declares a property named dataUpdater that's a block that takes two arguments.

  @property (copy, nonatomic) void (^dataUpdater)(NSString *key, id newValue);
  

• Performing one-time initialization [permalink]
  You can use libdispatch / Grand Central Dispatch, to execute a block that must run once, and only once, no matter how many threads are knocking at its door.

  + (void) initialize {
      static dispatch_once_t init_predicate;
  
      dispatch_once (&init_predicate, ^{ 
              CGColorSpaceRef rgbSpace = CGColorSpaceCreateDeviceRGB ();
  
              for (int i = 0; i < 7; i++) {
                  CGFloat components[] = { rawZoneColors[i]._red,
                                           rawZoneColors[i]._green,
                                           rawZoneColors[i]._blue,
                                           rawZoneColors[i]._alpha };
                  zoneColors[i] = CGColorCreate (rgbSpace, components);
              }
          });
  
  } // initialize
  

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