RxJs6:运算符函数与单类型运算符函数

我有以下代码:

export class EventsChainComponent { 
    eventSubscriber:Subscription;

    constructor (protected eventService: EventService) {}


    public registerComponentsEvent(event:any) {
        // getOnEvent signature
        // (method) EventService.getOnEvent(): Observable<FormEvent>
        this.eventSubscriber = this.eventService.getOnEvent()
            .pipe(filter((formEvent: FormEvent) => {return formEvent.key == event.event}))
            .subscribe((formEvent: FormEvent) => {
                  ..........
            });
    }

编译时,编译器返回以下错误:

所以,我搜索了一下,找到了 RxJs6

export declare function filter<T, S extends T>(predicate: (value: T, index: number) => value is S, thisArg?: any): OperatorFunction<T, S>;
export declare function filter<T>(predicate: (value: T, index: number) => boolean, thisArg?: any): MonoTypeOperatorFunction<T>;

如您所见,filter As 2重载方法,其中一个返回 OperatorFunction 还有一个 MonoTypeOperatorFunction .

有人能告诉我这两种类型的区别吗?有人知道我该怎么解决这个错误吗?

注:以下为 FormEvent 类是由我创建的,两者都是 EventService 和 EventsChainComponent 具有与引用同一类相同的导入。