Questions about using Futures and Completers

Question

Hey have I read all I can find about futures, but I would like some more advice on proper usage.

I am writing an API library, that bridges the gap between HTTP Requests and the app. So I use the future returned by HTTP in most cases, however sometimes the data is already retrieved. Is that the appropriate time to use a Completer?

ex.

String _someData = "";

Future<String> getSomeData(){
  if (_someData == ""){
    return Api.getSomeData().then((String someData){
      _someData = someData;
      return _someData;
    });
  } else {
    var completer = new Completer();
    completer.complete(_someData);
    return completer.future;
  }
}

-edit- Also if I create a Completer, but end up not using its future or calling complete. Will that cause a mem leak? Should I call its complete method or dispose of it somehow?

Thanks :)

Answer 1

Use an async function instead.

import "dart:async";

String _someData = "";

Future<String> getSomeData() async {
  if (_someData == "") {
    _someData = await Api.getSomeData();
  }

  return _someData;
}

Compiler generates approximately the following code:

import "dart:async";

String _someData = "";

Future<String> getSomeData() {
  var $_awaiter = new Completer<String>();
  try {
    if (_someData == "") {
      Api.getSomeData().then(($) {
        $_awaiter.complete($);
      }).catchError((e, s) {
        $_awaiter.completeError(e, s);
      });

      return $_awaiter.future;
    } else {
      $_awaiter.complete(_someData);
      return $_awaiter.future;
    }
  } catch (e, s) {
    $_awaiter.completeError(e, s);
    return $_awaiter.future;
  }
}