Block recursion and breaking retain cycle

Question

To better illustrate the question, consider the following simplified form of block recursion:

__block void (^next)(int) = ^(int index) {
    if (index == 3) {
           


        

Answer 1

To accomplish the retain-cycle-free recursive block execution, you need to use two block references - one weak and one strong. So for your case, this is what the code could look like:

__block __weak void (^weak_next)(int);
void (^next)(int);
weak_next = next = ^(int index) {
  if (index == 3) {
    return;
  }
  int i = index;
  weak_next(++i);
};
next(0);

Note that the block captures the weak block reference (weak_next), and the external context captures the strong reference (next) to keep the block around. Both references point to the same block.

See https://stackoverflow.com/a/19905407/1956124 for another example of this pattern, which also uses block recursion. In addition, the discussion in the comments section of the following article is relevant here as well: http://ddeville.me/2011/10/recursive-blocks-objc/