Returns an Awaitable of Vector after a mapping operation has been applied to each key and value in the provided KeyedTraversable


namespace HH\Asio;

function vmk<Tk, Tv, Tr>(
  KeyedTraversable<Tk, Tv> $inputs,
  (function(Tk,Tv):Awaitable<Tr>) $callable,
): Awaitable<Vector<Tr>>;

This function is similar to vm(), but passes element keys to the callable as well.

This function is similar to Vector::mapWithKey(), but the mapping of the keys and values is done using Awaitables.

This function is called vmk because we are returning a vector and doing a mapping operation that includes keys.

$callable must return an Awaitable.

The values in the Vector of the returned Awaitable are not available until you await or join the returned Awaitable.


  • $inputs - The KeyedTraversable of keys and values to map.
  • $callable - The callable containing the Awaitable operation to apply to $inputs.

Return Values



namespace Hack\UserDocumentation\API\Examples\HH\Asio\vmk;

 * Query an arbitrary number of URLs in parallel
 * returning them as a Vector of string responses.
async function get_urls(
  \ConstVector<string> $urls,
): Awaitable<Vector<string>> {

  // Await on curl requests in parallel and
  // prepend the request ID index
  return await \HH\Asio\vmk(
    async ($idx, $url) ==> {
      $content = await \HH\Asio\curl_exec($url);
      return $idx . " => " . $content;

$urls = ImmVector {

$pages = \HH\Asio\join(get_urls($urls));
foreach ($pages as $page) {
  echo substr($page, 0, 20) . ' ... ' . substr($page, -8);
0 => <!doctype html> ... </html>
1 => <!doctype html> ... </html>
2 => <!doctype html> ... </html>