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


function mmk<Tk, Tv, Tr>(
  KeyedTraversable<Tk, Tv> $inputs,
  (function(Tk,Tv):Awaitable<Tr>) $callable,
): Awaitable<Map<Tk, Tr>>

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

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

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

$callable must return an Awaitable.

The keys and values in the Map 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\mmk;

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

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

$urls = ImmMap {
  'com' => "http://example.com",
  'net' => "http://example.net",
  'org' => "http://example.org",

$pages = \HH\Asio\join(get_urls($urls));
foreach ($pages as $page) {
  echo substr($page, 0, 22) . ' ... ' . substr($page, -8);
com => <!doctype html> ... </html>
net => <!doctype html> ... </html>
org => <!doctype html> ... </html>