How to use the @ngrx/store.Reducer function in @ngrx/store

export function _createReducer(dispatcher, reducer) {
    return new Reducer(dispatcher, reducer);
}
export function _createStateIfExtension(extension, injector, initialState) {

export function _createReducer(dispatcher: DevtoolsDispatcher, reducer) {
  return new Reducer(dispatcher, reducer);
}

export function _createReducerIfExtension(extension, injector, reducer) {
    if (!!extension) {
        var devtoolsDispatcher = injector.get(DevtoolsDispatcher);
        return _createReducer(devtoolsDispatcher, reducer);
    }
    else {
        var dispatcher = injector.get(Dispatcher);
        return new Reducer(dispatcher, reducer);
    }
}
export function noMonitor() {

export function _createReducerIfExtension(extension: any, injector: Injector, reducer: any) {
  if (!!extension) {
    const devtoolsDispatcher: DevtoolsDispatcher = injector.get(DevtoolsDispatcher);

    return _createReducer(devtoolsDispatcher, reducer);
  }
  else {
    const dispatcher: Dispatcher = injector.get(Dispatcher);

    return new Reducer(dispatcher, reducer);
  }
}

useFactory(dispatcher: DevtoolsDispatcher, reducer) {
    return new Reducer(dispatcher, reducer);
  }
};