Returns an Awaitable of Map of ResultOrExceptionWrapper after a filtering operation has been applied to each key/value pair in the provided KeyedTraversable


namespace HH\Asio;

function mfkw<Tk, T>(
  KeyedTraversable<Tk, T> $inputs,
  (function(Tk,T):Awaitable<bool>) $callable,
): Awaitable<Map<Tk, HH\Asio\ResultOrExceptionWrapper<T>>>;

This function is similar to mfk(), except the Map in the returned Awaitable contains values of ResultOrExceptionWrapper instead of raw values.

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

This function is called mfkw because we are returning a map, doing a filtering operation on keys and values, and each value member in the Map is wrapped by a ResultOrExceptionWrapper.

$callable must return an Awaitable of bool.

The ResultOrExceptionWrappers in the Map of the returned Awaitable are not available until you await or join the returned Awaitable.


Return Values



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

// Return all non-negative odd numbers
// Positive evens filtered out,
// Negatives and zero cause exception
$odds = \HH\Asio\join(\HH\Asio\mfkw(
  Map {
    '-one' => -1,
    'zero' => 0,
    'one' => 1,
    'two' => 2,
    'three' => 3,
    'four' => 4,

  async ($num, $val) ==> {
    if ($val <= 0) {
      throw new \Exception("$num is non-positive");
    } else {
      return ($val % 2) == 1;

foreach($odds as $num => $result) {
  if ($result->isSucceeded()) {
    echo "$num Success: ";
  } else {
    echo "$num Failed: ";
-one Failed: string(20) "-one is non-positive"
zero Failed: string(20) "zero is non-positive"
one Success: int(1)
three Success: int(3)