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vfw

Note

This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information.

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

namespace HH\Asio;

function vfw<Tk, T>(
  KeyedTraversable<Tk, T, mixed> $inputs,
  (function(T): Awaitable<bool>) $callable,
): Awaitable<Vector<ResultOrExceptionWrapper<T>>>;

This function is similar to vf(), except the Vector in the returned Awaitable contains ResultOrExceptionWrappers instead of raw values.

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

This function is called vfw because we are returning a vector, doing a filtering operation and each member of the Vector is wrapped by a ResultOrExceptionWrapper.

$callable must return an Awaitable of bool.

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

Parameters​

Returns​

Examples​

<<__EntryPoint>>
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\vfw(
    Vector {-1, 0, 1, 2, 3, 4},

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

  foreach ($odds as $result) {
    if ($result->isSucceeded()) {
      echo "Success: ";
      \var_dump($result->getResult());
    } else {
      echo "Failed: ";
      \var_dump($result->getException()->getMessage());
    }
  }
}