Objective-C keywords: retain, assgin, copy, readonly, atomic, nonatomic, objective-cassgin

Objective-C keywords: retain, assgin, copy, readonly, atomic, nonatomic, objective-cassgin
Use of declarative attributes: declarative attributes are called the compile-time syntax @ property (retain, nonatomic) Some * s; @ property (parameter 1, parameter 2) Some * s; parameter 1: retain: Modify reference (object) Data Type assgin: Modify basic data type (default) copy: Some objects need to be copied to use NSString readonly: Read-only, only setter method, no getter Method
Parameter 2: Ensure the security of multithreading atomic: atomic threads are safe, but the efficiency is low (default) nonatomic: Non-atomic threads are not safe, but the efficiency is high