Amp Pattern Question

[withinboredom]

I'm rewriting a db driver to use Amp 1.x in Aerys. It's pretty straight forward, except that I hit a wall with how promises are implemented. Here's some example code that shows my issue:

function connect($options) {
  /* connect */
  Amp\onReadable($socket, function($watcherId) {
    /* read data */
    $inFlight[$token]->succeed($data); // $inFlight[$token] is the matching request for this query
}

function query($query) {
  /* Send query */
  $inFlight[$token] = new Amp\deferred();
  $promise = $inFlight[$token]->promise();
  return $promise->when(function($error, $data) use (/*lots of stuff from query send*/) {
    /* transform $data into native objects */
  }
}

function myCoRoutine() {
  $data = yield query($query);
}

However, $data in myCoRoutine holds the results of the original response from the server, before being transformed. Do you have any tips on how to get the result from the when in the query() function, instead of from the watcher?

[kelunik]

when doesn't work like then, it doesn't transform any value, it's a pure consumer. We know, it's strange that it's a fluent interface, we removed that in Amp v2.

You can either use Amp\pipe or a coroutine to transform the value:

<?php

function query($query) {
  /* Send query */
  $inFlight[$token] = new Amp\Deferred;
  return Amp\pipe($inFlight[$token]->promise(), function($data) use (...) {
    return ...;
  }
}

<?php

function query($query) {
  return Amp\resolve(function () use ($query) {
    $result = yield rawQuery(...);
    return transformRawQuery($result);
  });
}

[withinboredom]

Thanks for the quick response! Works like a charm.

[bwoebi]

Awesome! // closing as resolved.