associate object to class in swift.

SwfitObjectAssociateUtil

// refer to: http://rosettacode.org/wiki/Add_a_variable_to_a_class_instance_at_runtime#Swift
// this is stupid, just inherit the target class.
import Foundation

class ObjectAssociateUtil {
    static var objKeys = [String:UnsafePointer<()>]()
    
    class func getAssociateObject<T:AnyObject, D>(target:T, by_key key:String) -> D? {
        let objKeyName = "\(NSStringFromClass(target.dynamicType)).\(key)"
        if let objKey = objKeys[objKeyName] {
            return objc_getAssociatedObject(target, objKey) as? D
        }
        return nil
    }
    
    class func getAssociateObject<T:AnyObject, D>(target:T, by_key key:String, with_default defValue:D!) -> D {
        let objKeyName = "\(NSStringFromClass(target.dynamicType)).\(key)"
        if let objKey = objKeys[objKeyName] {
            return objc_getAssociatedObject(target, objKey) as! D
        }
        return defValue
    }

    class func setAssociateObject<T:AnyObject, D>(target:T, by_key key:String, set_obj_as obj:D!) {
        let objKeyName = "\(NSStringFromClass(target.dynamicType)).\(key)"
        
        var fooKey: UnsafePointer<()> = nil
        withUnsafePointer(&fooKey) { ptr in
            fooKey = UnsafePointer<()>(ptr)
        } // one way to define a unique key is a pointer variable that points to itself
        objKeys[objKeyName] = fooKey
        
        objc_setAssociatedObject(target, fooKey, obj as! AnyObject, objc_AssociationPolicy(OBJC_ASSOCIATION_RETAIN))
    }
}


import UIKit

extension UIView {
    var data:Int? {
        get {
            return ObjectAssociateUtil.getAssociateObject(self, by_key: "data")
        }
        
        set(newValue) {
            ObjectAssociateUtil.setAssociateObject(self, by_key: "data", set_obj_as: newValue)
        }
    }
    
    var name:String? {
        get {
            return ObjectAssociateUtil.getAssociateObject(self, by_key: "name")
        }
        
        set(newValue) {
            ObjectAssociateUtil.setAssociateObject(self, by_key: "name", set_obj_as: newValue)
        }
    }
    
    var count:Int {
        get {
            return ObjectAssociateUtil.getAssociateObject(self, by_key: "count", with_default: 0)
        }
        
        set(newValue) {
            ObjectAssociateUtil.setAssociateObject(self, by_key: "count", set_obj_as: newValue)
        }
    }
}


let v = UIView()
v.data = 1
v.name = "webee"

println(v.data!)
println(v.name!)
println(v.count)