ios - Swift closure in protocol extension -

i want decorate uiviewcontroller ability adjust it's interface when setinteractionenabled method called class (ex. network state manager). changes (if any) should provided in concrete controller overriding oninteractionchanged. here code:

import foundation  typealias interactionclosure = ((enabled: bool) -> void)  protocol interaction: class {      var oninteractionchanged: interactionclosure? { set }      func setinteractionenabled(enabled: bool)  }  extension interaction self: uiviewcontroller {      // default: nothing     // throws: - extensions may not contain stored properties     var oninteractionchanged: interactionclosure? = nil      func setinteractionenabled(enabled: bool) {         oninteractionchanged?(enabled: enabled)     }  }  extension uiviewcontroller : interaction {} 

how add default implementation oninteractionchanged?

answering own question don't do, here solution:

typealias interactionclosure = (enabled: bool) -> void  protocol interaction: class {      func addoninteractionchanged(closure: interactionclosure)     func setinteractionenabled(enabled: bool)  }  extension interaction self: uiviewcontroller {      func addoninteractionchanged(closure: interactionclosure) {         oninteractionchanged = closure     }      func setinteractionenabled(enabled: bool) {         oninteractionchanged?(enabled: enabled)     }      // mark: - private      private var oninteractionchanged: interactionclosure? {         {             let wrapper =                 objc_getassociatedobject(self, &icassociationkey) as? closurewrapper             return wrapper?.closure         }         set(newvalue) {             objc_setassociatedobject(self,                                      &icassociationkey,                                      closurewrapper(newvalue),                                      .objc_association_retain)         }     }  }  extension uiviewcontroller : interaction {}  // helpers  private var icassociationkey: uint8 = 0  private class closurewrapper {     var closure: interactionclosure?      init(_ closure: interactionclosure?) {         self.closure = closure     } } 

client class:

class loginviewcontroller: uiviewcontroller {      // mark: - lifecycle      override func viewdidload() {         super.viewdidload()         self.setup()     }      // mark: - private      private func setup() {         // ...          addoninteractionchanged { [unowned self] (enabled) in                         self.signinbutton.enabled = enabled             self.activityindicatorview.hidden = !enabled         }     }  } 

in manager class:

visibleviewcontroller?.setinteractionenabled(true)