The difference between atomic/nonatomic and retain/assign in iOS

Atomic: Atomic operation, providing operation protection in multi-threaded environment;

Nonatomic: Non-atomic operation, does not provide protection, in the multi-threaded environment may occur unknown error;

Retain: Hold reference, that is, the reference count value of the object count + = 1, the resulting object and the incoming object point to the same memory space, equivalent to the pointer assignment;

Assign: Assignment operation opens up new space in memory and copies incoming parameters/objects for your own use.

The difference between atomic/nonatomic and retain/assign in iOS