title: angular2 extend service with argument in constructor
body: <p>I have some problems in understanding how to extend correctly a service in angular2, maybe because I don't understand well how to extend a class in typescript.</p>
  
  <h1> SuperClass</h1>
  
  <pre><code>@Injectable()
  export class CallService{
      constructor(private errror:string){
          this.errMsg=errror;
      }
      private _errMsg:string;
      set errMsg(arg0:string){
          this._errMsg=arg0;
      }
      get errMsg():string{
          return this._errMsg;
      }
  }
  </code></pre>
  
  <h1>SubClass</h1>
  
  <pre><code>@Injectable()
  export class DownloadService extends CallService{
      constructor(private error:string,private http:Http){
          super(error)
      }
  }
  </code></pre>
  
  <h1>App.Component</h1>
  
  <pre><code>@Component({
  selector:'my-app',
      templateUrl:'app/app.component.html',
      styleUrls:['app/app.component.css'],
      directives:[ROUTER_DIRECTIVES,WaitComponent],
      providers:[DownloadService,SwitcherService,CallService,WaitService]
  })
  export class AppComponent{
      title:'App'
      constructor(
          private areadownloadservice:AreaDownloadService,
          private waitService:WaitService,
          private switcherservice:SwitcherService,
          private callService:CallService){}
      )
  }
  </code></pre>
  
  <p>What I want to do is to extend some classes with CallService so that all class that make a calls will have a errMsg string property to set or get, but I get this exception:</p>
  
  <blockquote>
    <p>No provider for String!</p>
  </blockquote>
  
  <p>What did I missed?</p>