interface DataCollector
{
    /**
      * @return array of results in the exact same order as references. 
      * Use null if no associated value found
      */
    public function collect(Reference ...$references): array
}

[$promises, $refrences] = $this->collectReferences()
$resolved = $dataCollector->collect($references);
foreach($resolved as $i => $resolvedValue) {
    $promises[$i]->resolve($resolvedValue);
}

$dataCollectors: !tagged export.data_collector