AssociatedObjects

Works, but experimental.

Associate objects and values with any instance of any class. The associated objects/values automatically go away after the instance is deinited (but see issues below).

Issues:

• Associated objects stay alive unless internal clean-up is performed, although this does happen automatically whenever the associate(value:withKey:) and associatedValue(forKey:) methods are called. So as long as the interface is being used regularly (on any instance), it's ok.
• No attempt whatsoever to make it thread safe yet, recommend only using from main thread for now.

Using

Import the framework:

import AssociatedObjects

Any classes you want to use this feature on need to be made Associable:

extension SomeClass: Associable {}

Then just call the methods defined in the Associable protocol:

someClassInstance.associate(value: 7, withKey: "anInt")
someClassInstance.associate(value: anyObjectInstance, withKey: "anObject")

// Later...

let theInt = someClassInstance.associatedValue(forKey: "anInt") as? Int
let theObject = someClassInstance.associatedValue(forKey: "anObject") as? AnyObject