__strong and __weak

ARC Two concepts: strong pointers and weak pointers

By default, any pointer is a strong pointer

A pointer decorated with __weak as a weak pointer

Without any strong pointers pointing to the object, the object will be destroyed

Two objects should be noted when referencing one another with weak, one with strong (e.g. delegate)

UI controls are typically decorated with weak (or strong) (the controller's view has a subviews array control, and all child views on the view are present as long as the controller is in it)

__strong and __weak