Question

In @mmalc’s response to this question he states that ‘In general you should not use accessor methods in dealloc (or init).’ Why does mmalc say this?

The only really reasons I can think of are performance and avoiding unknown side-effects of @dynamic setters.

Discussion?

Answer 1

It is all about using idiomatically consistent code. If you pattern all of your code appropriately there are sets of rules that guarantee that using an accessor in init/dealloc is safe.

The big issue is that (as mmalc said) the code the sets up the properties default state should not go through an accessor because it leads to all sorts of nasty issues. The catch is that there is no reason init has to setup the default state of a property. For a number of reasons I have been moving to accessors that self initialize, like the simple example below:

- (NSMutableDictionary *) myMutableDict {     if (!myMutableDict) {         myMutableDict = [[NSMutableDictionary alloc] init];     }      return myMutableDict; } 

This style of property initialization allows one to defer a lot of init code that may not actually be necessary. In the above case init is not responsible for initing the properties state, and it is completely safe (even necessary) for one to use the accessors in the init method.

Admittedly this does impose additional restrictions on your code, for instance, subclasses with custom accessors for a property in the superclass must call the superclasses accessor, but those restrictions are not out of line with various other restrictions common in Cocoa.