What is objc_setAssociatedObject() and in what cases should it be used?

Question

In a project I have taken on, the original author has opted to use objc_setAssociatedObject() and I\'m not 100% clear what it does or why they decided to use it

Answer 1

To answer your revised question:

What is the point in associating the device with the view controller if it's already an instance variable?

There are several reasons why you might want to do this.

• the Device class doesn't have a controller instance variable, or property and you can't change it or subclass it e.g. you don't have the source code.
• you want two controllers associated with the device object and you can't change the device class or subclass it.

Personally, I think it is very rare to need to use low level Objective-C runtime functions. This looks like a code smell to me.