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

namespace HH\Asio;

function mfw<Tk as arraykey, T>(
  KeyedTraversable<Tk, T> $inputs,
  (function(T): Awaitable<bool>) $callable,
): Awaitable<Map<Tk, ResultOrExceptionWrapper<T>>>;

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

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

This function is called mfw because we are returning a map, doing a filtering operation 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.




async function basic_usage_main(): Awaitable<void> {
  // Return all non-negative odd numbers
  // Positive evens filtered out,
  // Negatives and zero cause exception
  $odds = await \HH\Asio\mfw(
    Map {
      '-one' => -1,
      'zero' => 0,
      'one' => 1,
      'two' => 2,
      'three' => 3,
      'four' => 4,

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

  foreach ($odds as $num => $result) {
    if ($result->isSucceeded()) {
      echo "$num Success: ";
    } else {
      echo "$num Failed: ";