Composing Results

Responses in dispatch are wrapped up in a scala Future. The Future represents the potential "result" of the asynchronous http call. The dispatch Future is obtained from a promise inside the dispatch library. dispatch makes an anysnchronous call, completes the promise, which then signals that the Future has a value available. async-http-client can return a java Future, but a java and scala Future are different.

When managing responses there are a few ways to manage the Future value as well as the body. This section is about composing results which is really about composing Future's. You can find a bounty of literature on composing Futures on the web and we are not try to repeat or summarize that corpus here.

There are a few topics though:

• Future management with dispatch's Future's enhancements

• async macro

• Miscellaneous Topics

  • Retries

  • Interrupting requests (TODO)

Note that composing results really means composing the "containers" that hold our results, which in this case is a scala Future. This chapter will cover a few ways of composing Futures such as the use of scala async, however, there are libraries such as fetch that have been created to compose functions that have high latency--which is often the case for http calls. These are covered in another chapter.