A note on how to work with ARC, Objective-C blocks and C libraries. (久利寿でも分かりにくかったので共有いたします！)

gistfile1.m

//A note on how to work with ARC, Objective-C blocks and C libraries.
//with love from kristopher on a Sunday (2013.2.3@5:46a JST)
//License: Public-Domain

//あるLibraryのAsync Callback TypeDef
typedef void (somelibrary_doasync_cb)(int state, uintptr_t user_data);
//あるLibraryのAsync Function
void somelibrary_doasync(somelibrary_doasync_cb callback, uintptr_t user_data);
//われわれのBlockDef
typedef void (^StatusHandlerBlock)(int state);
//われわれのCallback:
void my_callback(int state, uintptr_t user_data);

//To C land (Cの世界へ)
- (void) doSomethingAsyncWithBlock: (StatusHandlerBlock)response_block {
  //Blocks are actually NSObjects, so we have to copy and __bridge_retained the pointer 
  (void)somelibrary_doasync(my_callback, (uintptr_t)(__bridge_retained CFTypeRef)([response_block copy]) );
}

//From C land (Cの世界から)
void my_callback(int state, uintptr_t user_data) {
  //...
  __block StatusHandlerBlock block_handler = (__bridge_transfer StatusHandlerBlock)(CFTypeRef)user_data;
  block_handler(state);
  block_handler = nil; //ARCだからpsudo-release when done.
  //...
}