ios - Immutable value type [string] only has mutating members named append -

i'm trying append new store object stores array in user struct...i added mutating func append struct i'm still missing i'm still getting the

immutable value type [store] has mutating members named 'append'

error

import foundation  import uikit  struct user {     var name: string     var stores: [store]        mutating func append(newstore: store) {         stores.append(newstore)     } }  extension user: printable {     var description: string {         var printedname = ("\(name string, stores [store])")         return printedname     } }  struct store {     var name: string     var data: [[string: string]]    }  extension store: printable {     var description: string {         var printedstores = ("\(name string, data [[string : string]])")         return printedstores } }   @ibaction func done(segue: uistoryboardsegue) {         let addstoreviewcontroller = segue.sourceviewcontroller as! addstoreviewcontroller         let store = addstoreviewcontroller.store         if let selectedindex = addstoreviewcontroller.index {             stores[selectedindex] = store!         } else {             if let selecteduser = user {                 selecteduser.stores.append(store!)             }         }         storetableview.reloaddata()     }  import uikit  class addstoreviewcontroller: uiviewcontroller {       var store: store?     var index: int?      @iboutlet weak var storetextfield: uitextfield!      override func viewdidload() {         super.viewdidload()          if let name = store?.name {             storetextfield?.text = name         }          // additional setup after loading view.     }          // mark: - navigation       override func prepareforsegue(segue: uistoryboardsegue, sender: anyobject?) {         let name = storetextfield?.text         if segue.identifier == "addaction" {             if var store = store {                 self.store?.name = name!             } else {                 store = store(name: name!, data: [["": ""]])                 println(store)              }         }     }    } 

if let selectedindex = addstoreviewcontroller.index {     stores[selectedindex] = store! } else {     if let selecteduser = user {         selecteduser.stores.append(store!)     } } 

this appears problem section.

we can both simultaneously fix problem and clean else code bit:

if let store = store, selectedindex = addstoreviewcontroller.index {     stores[selectedindex] = store } else if let store = store, var selecteduser = user {     selecteduser.append(store) } 

we're able append correctly, don't have unnecessary level of nesting, , don't have force unwrap (which leads crashes).