Objective-C Blocks, Recursion Fails

Question

Sup guys,

I\'m trying to do a function that calls itself but by putting everything on one block,

As you can see, the following function is intended to be cal

Answer 1

You have to declare your block itself as a block variable:

__block void (^_test_closure)();


_test_closure = ^{
    NSLog(@"Running...");
    if ((arc4random() % 100) > 50) {
        _test_closure();
    }
}

_test_closure();

Answer 2

It works with XCode 5 - no warnings, no retain cycles:

typedef void(^blockT)();

blockT block1;
blockT __block block1recursive;

block1recursive = block1 = ^(){
    block1recursive();
};

block1();

Answer 3

Recursion and blocks is tricky. Because a block captures all variables passed in, the variable _test_closure is not initialized yet (and clang should give you a warning:

Block pointer variable '_test_closure' is uninitialized when captured by block

).

There are several ways you can get around this, but the most obvious & simplest is to just make the block itself a __block variable (what @H2CO3 said). This allows the block to be weak-linked almost, so that when you call it again, it is properly initialized.

Another option you have is making the block a global or static, like this:

// outside of 'main', thus being a global variable
void (^blockRecurse)(int) = ^(int level) {
    if (level < 0)
        return;
    NSLog(@"Level: %i", level);
    blockRecurse(--level);
};

int main()
{
    @autoreleasepool {
        blockRecurse(10);
    }
} 

This means it's not being captured by the block, but instead it's referencing the global / static variable, which can be changed by all code equally.