Sample code to illustrate different types of blocks— global. heap, and stack.

gistfile1.m

//
//  main.m
//  BlocksRuntime
//
//  Created by Jim Dovey on 11-07-22.
//  Copyright 2011 Jim Dovey. All rights reserved.
//

#import <Foundation/Foundation.h>

// from Block_private.h in libclosure for Lion
extern const char * _Block_dump(const void *block);
typedef void (^test_block_t)(int i);

static void global_block_example(void)
{
	printf("\n\nGLOBAL BLOCKS\n\n");
	
	// this block will be made global because it doesn't pull in any values from the stack,
	// thus causing the compiler to allocate it globally.
	test_block_t block = ^(int i) {
		printf("Pure global block was passed %d\n", i);
	};
	
	block(42);
	
	printf("This is the pure global block's debug information before copy:\n%s\n",
		   _Block_dump((__bridge const void *)block));
	
	block = [block copy];		// using ObjC methods so ARC can clean it up
	printf("This is the pure global block's debug information after copy:\n%s\n",
		   _Block_dump((__bridge const void *)block));
}

static void heap_block_example(void)
{
	printf("\n\nHEAP BLOCKS\n\n");
	
	__block int j = 27;
	
	// this block will be allocated on the heap since it uses a __block variable and isn't outside
	test_block_t globalBlock = ^(int i) {
		printf("Global block with __block variable was passed %d\n", i);
		j += i;
	};
	
	globalBlock(42);
	printf("After running the block, j is %d\n", j);
	globalBlock(87);
	printf("After running the block, j is %d\n", j);
	
	printf("This is the debug information of a global block with a __block argument before copy:\n%s\n",
		   _Block_dump((__bridge const void *)globalBlock));
	
	globalBlock = [globalBlock copy];
	printf("This is the debug information of a global block with a __block argument after copy:\n%s\n",
		   _Block_dump((__bridge const void *)globalBlock));
}

static void stack_block_example(dispatch_block_t block)
{
	printf("\n\nSTACK BLOCKS\n\n");
	
	printf("This is the debug information of a passed-in stack-based block:\n%s\n",
		   _Block_dump((__bridge const void *)block));
	
	block();
	block = [block copy];
	
	printf("This is the debug information of a copied stack-based block:\n%s\n",
		   _Block_dump((__bridge const void *)block));
	
	block();
}

int main (int argc, const char * argv[])
{
	@autoreleasepool
	{
		printf("This is an inline block's debug information:\n%s\n", _Block_dump((__bridge const void *)^{
			printf("I am an inline block.\n");
		}));
		
		global_block_example();
		heap_block_example();
		
		stack_block_example(^{
			printf("Inline stack (?) block: argc = %d\n", argc);
		});
	}
	
    return ( 0 );
}