问题
XCode accepts it. But will retain be applied when I internally set the property (no setter outside since readonly but when I initialize the value in a class method) ?
Regards, Apple92
回答1:
The reason to do this is to allow you to do @property (retain) in a class continuation or category. If you don't have the retain on the outer property, you will get a warning about the properties being mismatched.
回答2:
You might specify (readonly, retain) for a publicly-facing property, and then inside your .m, re-define it as (readwrite, retain) to be able to assign to it privately. I use this pattern myself occasionally.
回答3:
it's also nice as a form of interface documentation
来源：https://stackoverflow.com/questions/3894888/does-property-readonly-retain-have-a-meaning