I have the following code under ARC:
-(void) foo {
__block int spam = 42;
self.myProperty = ^{
spam++;
}
self.myProperty(); // Increment first time
}
-(void) bar {
self.myProperty(); // Increment second time
}
When "Increment first time" is called, ObjC uses pointer to spam (which resides on stack) to increment it, right?
After it, foo stack is thrown out, so pointer is not valid anymore.
What will bar do? What should happen when I call it?
Everything is clear about objects, since they are created on heap and block copying (which takes place in the moment of property assignment) leads to retain call. But what is about auto vars?
I can use debugger to find the answer, but I want to fully understand it: which part of Objc/clang specification covers that?
Update: A used "&" to get address of my variable and found that address get changed in the moment I assign block to my property (actually at the moment when block is copied). I believe that is the moment from my variable was moved from stack to heap.
-(void) foo {
__block int spam = 42;
int* addrOfSpam = &spam;
*addrOfSpam = 43; // OK, spam = 43 now
self.myProperty = ^{ // The moment when spam is moved from stack to heap
spam++;
};
*addrOfSpam = 44; // Fail, spam not changed and 'addrOfSpam' points to nowhere
spam++; // Spam looks like auto/stack var here, BUT IT IS NOT!
// It is on heap now, and "spam" is changed by compiler to:
// *(newAddressOfSpamInHeap_OnlyCompilerKnowsWhere)++;
}
