如果我的属性没有setter（只读），如果它不是NSNumber或NSValue，UIKit是否保留该值？

I want to figure out in which cases I need to care about memory management when it comes to properties. I wrote down something from a site I don't remember anymore, where they said that if a property has any value other than NSNumber or NSValue, and if it has no setter, then UIKit would autorelease the old value and retain the new one. Although I dont get it why UIKit would set anything if there is no setter (directly to the value, I guess).I want to figure out in which cases I need to c