Issues with double pointers in ARC

Question

I have some variables, which cache some data from a webservice.

To make my code more dynamic, I want to return a double pointer to the cache-variable. So it's a double pointer. I have some issues doing this with ARC.

Here's what I got:

- (id *)pointerToSectionCacheProperty:(SomeSection)section {
    switch (section) {
        case Section1:
        {
            return &_section1Cache;
        }
            break;
        case Section2:
        {
            return &_section2Cache;
        }
            break;
        case Section3:
        {
            return &_section3Cache;
        }
            break;
    }

    return nil;
}

ARC gives me the following error:

Returning 'NSArray *__strong *' from a function with result type '__autoreleasing id *' changes retain/release properties of pointer

Is this the wrong approach?

If so, what is the right approach?

What purpose does the double pointer serve? ARC is simply confused, function results are autorelease by default, what does your NSArray * have as its declarations? — ImHuntingWabbits, Sep 17 '13 at 18:10
I believe the correct decl would be (strong NSArray **) since the caller will effectively have to manage that object on their own if they change the value. — ImHuntingWabbits, Sep 17 '13 at 18:16
Hah I really should learn ARC. You should also mark it as answered. — ImHuntingWabbits, Sep 17 '13 at 18:47
See also [this answer](http://stackoverflow.com/questions/8814718/handling-pointer-to-pointer-ownership-issues-in-arc/8829294#8829294) - it is not exactly the same situation, as it is directed at passing pointers to pointers *into* methods and not receiving them *from* methods, but the same principles apply. HTH. — CRD, Sep 17 '13 at 19:40

score 1 · Accepted Answer · answered Sep 17 '13 at 18:23

Solution

Got it working like this:

- (NSArray *__strong *)pointerToSectionCacheProperty:(SomeSection)section {
    switch (section) {
        case Section1:
        {
            return &_section1Cache;
        }
            break;
        case Section2:
        {
            return &_section2Cache;
        }
            break;
        case Section3:
        {
            return &_section3Cache;
        }
            break;
    }

    return nil;
}

As a sidenote, - (id __strong *)... will work just as well.

Issues with double pointers in ARC

1 Answers1

Solution