Can an Objective-C object be deallocated while an instance method is being invoked on it?

Question

Consider the following: An instance of an Objective-C class is referenced by one strong reference and one weak reference (under ARC). On thread X, a method is called on the

Answer 1

ARC actually does retain weak references before calling instance methods on them, and releases after the call.

I was researching this issue and was corrected by a colleague after showing him this stackoverflow question. He pointed to this: http://lists.apple.com/archives/objc-language/2012/Aug/msg00027.html

Sure enough, in the assembly, ARC retains and releases around an invocation on a weak reference.

One time you will want to listen to CLANG_WARN_OBJC_RECEIVER_WEAK is for nil checks, when nil could cause an error.

if (self.weakRefToParent) {
    //self.weakRefToParent could be dealloced and set to nil at this line
    NSString *name = [self.weakRefToParent name]; //CLANG_WARN_OBJC_RECEIVER_WEAK warning
    [self.namesArray addObject:name];  //name is nil, NSInvalidArgumentException
}

This is the safer way:

Parent *strongRefToParent = self.weakRefToParent;
if (strongRefToParent) {
    NSString *name = [strongRefToParent name];
    [self.namesArray addObject:name];
}