仓库之间的差异。选择进入施工器并在其之前以角6?

1) export class SomeClass {
      myObservable$ = <Observable<MyObservableType>>this.store.select(fromReducers.getMyObservable);
      constructor(
        private store: Store<fromReducers.State>
      ) { }
    } 

2) export class SomeClass {
      myObservable$ = Observable<MyObservableType>;
      constructor(
        private store: Store<fromReducers.State>
      ) {
        this.myObservable$ = this.store.select(fromReducers.getMyObservable);
      }
    }

为什么在ngrx/商店 app-example 他们使用第二种变体?