function fetchResults (searchText) {
    var items = $scope.$parent.$eval(itemExpr),
        term  = searchText.toLowerCase(),
        isList = angular.isArray(items),
        isPromise = !!items.then; // Every promise should contain a `then` property

    if (isList) onResultsRetrieved(items);
    else if (isPromise) handleAsyncResults(items);

    function handleAsyncResults(items) {
      if (!items) return;

      items = $q.when(items);
      fetchesInProgress++;
      setLoading(true);

      $mdUtil.nextTick(function () {
          items
            .then(onResultsRetrieved)
            .finally(function(){
              if (--fetchesInProgress === 0) {
                setLoading(false);
              }
            });
      },true, $scope);
    }

    function onResultsRetrieved(matches) {
      cache[term] = matches;

      // Just cache the results if the request is now outdated.
      // The request becomes outdated, when the new searchText has changed during the result fetching.
      if ((searchText || '') !== ($scope.searchText || '')) {
        return;
      }

      handleResults(matches);
    }
  }
Fetches the results for the provided search text.
@param searchText