Question

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What describes @property(…) best? What's that actually good for?

If I declare a variable in my class interface, I can use such variable anywhere on my class. Awesome.

If I use @property (retain) Something *myVar; I can access that variable with self.myVar… But, what is the difference? Is there a good reason I should use one method or another?

Answer 1

Short answer: Encapsulation of memory management.

Longer answer: You need to establish ownership of an object if you want to use it later. If you want to use it later, you’ll need a reference to it with which to do so, and a great place to keep that reference is in an instance variable.

You could handle the ownership claims (i.e. retains and releases) each time you assign a new value to that, but that would leave a lot of repetitious and trouble-prone boilerplate code scattered all over the place, like cherries in a fruitcake. That kind of mess is fiendishly difficult to debug when (not if) something goes wrong. So, it’s far better to wrap that code up in accessor methods, so you can write it once and then forget about it.

But accessor methods are mostly boilerplate too, so we use @property declarations to create them automagically, rather than writing them by hand.

Edit: Apple’s Memory Management Guide provides a lot of detail about what the accessor methods generated by @property do behind the scenes.