Is it possible to extend all existing Swift objects as when adding a category over NSObject in Objective C?
According to this article, all Swift objects inherit from the SwiftObject class, but I can't add an extension to it.
Is there any solution to this?
No. Swift objects do not actually inherit from any root base class. The compiler may insert one as an implementation detail, but the language does not have this.
The solution is a function, and usually a generic function, rather than a method. Something that applies to "every kind of object" isn't really encapsulated. There are very few actions that apply to every conceivable thing in the universe. But functions can map absolutely anything to absolutely anything else, so are a better tool here.
Just as a note, not all objects inherit from NSObject either, and it's not a language requirement. But you're correct that the vast majority do. Take a look at NSProxy for the top of a non-NSObject tree (it implements the NSObject protocol, but does not inherit from the NSObject class). That's why id is not the same thing as NSObject*.
To your question about associated objects, this is built-in:
import Foundation
class Thing { }
let thing = Thing()
var MyKey: Character = "0"
objc_setAssociatedObject(thing, &MyKey, "I'm a value!", objc_AssociationPolicy(OBJC_ASSOCIATION_COPY))
println(objc_getAssociatedObject(thing, &MyKey))
Is this what you were trying to create? Note that objc_setAssociatedObject is also a function, not a method, in ObjC.
