将类成员的类型设置为通用参数的子类型

Question

我上了这个课：

export class Route <Req = any, Res = any, ReqBody = any, ResBody = any>{

  requestClass: Req;
  responseClass: Res;
  requestBodyClass: ReqBody;
  responseBodyClass: ResBody;

  constructor(){

  }

  setRequestType(v: Req): Req {
    this.requestClass = v;
    return v;
  }

  setResponseType(v: Res): Res{
    this.responseClass = v;
    return v;
  }

  setResponseBodyType(s: ResBody): ResBody {
    this.responseBodyClass = s;
    return s;
  }

  setRequestBodyType(s: ReqBody): ReqBody {
    this.requestBodyClass = s;
    return s;
  }

}

我的问题-有没有办法做这样的事情：

  requestClass: Req;
  responseClass: Res;
  requestBodyClass: ReqBody !== any ? ReqBody : Req['body'];
  responseBodyClass: ResBody !== any ? ResBody : Res['body'];

似乎不太可能执行类似的操作，但是，如果用户没有为ReqBody或ResBody传递类型，则我想将Req或Res上的body值默认为默认值。