Is it possible in Swift to add variables to an object at runtime? -

specifically, add variable of type enum instance of uiview, without subclassing or create extension.

thanks.

the previous answer objc_setassociatedobject() right approach, think apple's apis have not yet been vetted, because i've had difficulty using them way think ought used. (i shouldn't have muck unsafe pointers , such.) here's solution i'm using now.

first, need bit of objective-c glue (follow apple's instructions mixing objective-c , swift in same project:

// runtimeglue.h // should included bridging header.  @import foundation;  void setassociatedobject_glue(nsobject *object, const nsstring *key, nsobject *value); nsobject *getassociatedobject_glue(nsobject *object, const nsstring* key);   // runtimeglue.m  #import "runtimeglue.h" #import <objc/runtime.h>  void setassociatedobject_glue(nsobject *object, const nsstring *key, nsobject *value) {     objc_setassociatedobject(object, (__bridge const void *)(key), value, objc_association_retain_nonatomic); }  nsobject *getassociatedobject_glue(nsobject *object, const nsstring* key) {     return objc_getassociatedobject(object, (__bridge const void *)(key)); } 

next, swift methods you'll call rest of program:

// runtime.swift  import foundation  public func setassociatedobject(#object: nsobject, #key: nsstring, #value: nsobject?) {     setassociatedobject_glue(object, key, value) }  public func getassociatedobject(#object: nsobject, #key: nsstring) -> nsobject? {     return getassociatedobject_glue(object, key) } 

finally, example of use tag particular view controller's view "debugging".

// myviewcontroller.swift  import uikit  let debugkey: nsstring = "debugkey"  class myviewcontroller: uiviewcontroller {     override func viewdidload() {         super.viewdidload()          setassociatedobject(object: self.view, key: debugkey, value: "debugging")     }      override func viewwillappear(animated: bool)  {         super.viewwillappear(animated)          let val = getassociatedobject(object: self.view, key: debugkey)         println("val:\(val)")     } } 

this approach lets pass nil value setter in order clear value key, , returns optional getter. note key argument must identical in both cases (k1 === k2) , not merely equivalent (k1 == k2).

also note lets tag instances of nsobject or subclasses-- not work swift native classes. value must nsobject subclass, both strings , number literals automatically bridge objective-c, don't need explicit casting.