AssociatedObjects.swift

private var AssociatedKey: UInt = 1

private final class AssociatedObjectBox<T> {
    let value: T
    
    init(_ x: T) {
        value = x
    }
}

private func lift<T>(x: T) -> AssociatedObjectBox<T> {
    return AssociatedObjectBox(x)
}

private func setAssociatedObject<T>(object: AnyObject, value: T, key: UnsafePointer<Void>, policy: objc_AssociationPolicy) {
    if let v: AnyObject = value as? AnyObject {
        objc_setAssociatedObject(object, key, v,  policy)
    } else {
        objc_setAssociatedObject(object, key, lift(value), policy)
    }
}

private func getAssociatedObject<T>(object: AnyObject, key: UnsafePointer<Void>) -> T? {
    if let v = objc_getAssociatedObject(object, key) as? T {
        return v
    } else if let v = objc_getAssociatedObject(object, key) as? AssociatedObjectBox<T> {
        return v.value
    } else { 
        return nil 
    }
}