Question

Does the following line leak this object [[NSMutableDictionary alloc] init] ?

[myCollection setObject:[[NSMutableDictionary alloc] init] forKey:@"myDictionary"];

I assume it doesn’t because the object is never assigned to a reference… but at the same time I question it because I did alloc the object…

Would the following work as an alternative?

[myCollection setObject:[NSMutableDictionary dictionary] forKey:@"myDictionary"];

Answer 1

The first will leak, the second will not.

Assigning an object reference into a variable does not affect ownership of the object at all. You invoked alloc, which means that you are the owner, regardless of whether you capture the results of that call at all. If you don’t, you’ve leaked.

The second option ([NSMutableDictionary dictionary]) will not leak, since +dictionary returns a non-owned (autoreleased) object.

So in a nutshell, your intuition is correct. Congratulations! Many people who ask memory management questions here usually get it wrong. 🙂