extension may not contain stored properties and no member problems in swift -

i not able understand why getting these errors. please me. here source code

import uikit import avfoundation  // mark: - playsoundsviewcontroller: avaudioplayerdelegate  extension playsoundsviewcontroller: avaudioplayerdelegate {      var audioengine = avaudioengine()       // mark: alerts      struct alerts {     static let dismissalert = "dismiss"     static let recordingdisabledtitle = "recording disabled"     static let recordgindisabledmessage = "youve disabled app recording microphone. check settings"     static let recodingfailedtitle = "recording failed"     static let recordingfailedmessage = "something went wrong recording"     static let audiorecordederror = "audio recorder error"     static let audiosessionerror = "audio session error"     static let audiorecordingerror = "audio recording error"     static let audiofileerror = "audio file error"     static let audioengineerror = "audio engine error"     }      // mark: playingstate (raw values correspond sender tags)      enum playingstate { case playing, notplaying }      // mark: audio functions      func setupaudio() {         // initialize (recording) audio file         {             audiofile = try avaudiofile(forreading: recordedaudiourl url)         } catch {             showalert(alerts.audiofileerror, message: string(describing: error))         }             }      func playsound(rate: float? = nil, pitch: float? = nil, echo: bool = false, reverb: bool = false) {          // initialize audio engine components         audioengine = avaudioengine()          // node playing audio         audioplayernode = avaudioplayernode()         audioengine.attach(audioplayernode)          // node adjusting rate/pitch         let changeratepitchnode = avaudiounittimepitch()         if let pitch = pitch {             changeratepitchnode.pitch = pitch         }         if let rate = rate {             changeratepitchnode.rate = rate         }         audioengine.attach(changeratepitchnode)          // node echo         let echonode = avaudiounitdistortion()         echonode.loadfactorypreset(.multiecho1)         audioengine.attach(echonode)          // node reverb         let reverbnode = avaudiounitreverb()         reverbnode.loadfactorypreset(.cathedral)         reverbnode.wetdrymix = 50         audioengine.attach(reverbnode)          // connect nodes         if echo == true && reverb == true {             connectaudionodes(audioplayernode, changeratepitchnode, echonode, reverbnode, audioengine.outputnode)         } else if echo == true {             connectaudionodes(audioplayernode, changeratepitchnode, echonode, audioengine.outputnode)         } else if reverb == true {             connectaudionodes(audioplayernode, changeratepitchnode, reverbnode, audioengine.outputnode)         } else {             connectaudionodes(audioplayernode, changeratepitchnode, audioengine.outputnode)         }          // schedule play , start engine!         audioplayernode.stop()         audioplayernode.schedulefile(audiofile, at: nil) {              var delayinseconds: double = 0              if let lastrendertime = self.audioplayernode.lastrendertime, let playertime = self.audioplayernode.playertime(fornodetime: lastrendertime) {                  if let rate = rate {                     delayinseconds = double(self.audiofile.length - playertime.sampletime) / double(self.audiofile.processingformat.samplerate) / double(rate)                 } else {                     delayinseconds = double(self.audiofile.length - playertime.sampletime) / double(self.audiofile.processingformat.samplerate)                 }             }              // schedule stop timer when audio finishes playing             self.stoptimer = timer(timeinterval: delayinseconds, target: self, selector: #selector(playsoundsviewcontroller.stopaudio), userinfo: nil, repeats: false)             runloop.main.add(self.stoptimer!, formode: runloopmode.defaultrunloopmode)         }          {             try audioengine.start()         } catch {             showalert(alerts.audioengineerror, message: string(describing: error))             return         }          // play recording!         audioplayernode.play()     }      func stopaudio() {          if let audioplayernode = audioplayernode {             audioplayernode.stop()         }          if let stoptimer = stoptimer {             stoptimer.invalidate()         }          configureui(.notplaying)          if let audioengine = audioengine {             audioengine.stop()             audioengine.reset()         }     }      // mark: connect list of audio nodes      func connectaudionodes(_ nodes: avaudionode...) {         x in 0..<nodes.count-1 {             audioengine.connect(nodes[x], to: nodes[x+1], format: audiofile.processingformat)         }     }      // mark: ui functions      func configureui(_ playstate: playingstate) {         switch(playstate) {         case .playing:             setplaybuttonsenabled(false)             stopbutton.isenabled = true         case .notplaying:             setplaybuttonsenabled(true)             stopbutton.isenabled = false         }     }      func setplaybuttonsenabled(_ enabled: bool) {         snailbutton.isenabled = enabled         chipmunkbutton.isenabled = enabled         rabbitbutton.isenabled = enabled         vaderbutton.isenabled = enabled         echobutton.isenabled = enabled         reverbbutton.isenabled = enabled     }      func showalert(_ title: string, message: string) {         let alert = uialertcontroller(title: title, message: message, preferredstyle: .alert)         alert.addaction(uialertaction(title: alerts.dismissalert, style: .default, handler: nil))         self.present(alert, animated: true, completion: nil)     } } 

the screenshot of error in link below.

screenshot!

you can not declare var audioengine = avaudioengine() inside extension. declare inside playsoundsviewcontroller class instead.

extensions meant augment behaviours, not fundamentally change class.

@source: why can't add stored properties extensions?