hphp/hack/manual/apis/Functions/HH.Asio/vf.md
:::info[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 after a filtering operation has been
applied to each value in the provided KeyedTraversable
namespace HH\Asio;
function vf<Tk, T>(
KeyedTraversable<Tk, T, mixed> $inputs,
(function(T): Awaitable<bool>) $callable,
): Awaitable<Vector<T>>;
This function is similar to Vector::filter(), but the filtering of the
values is done using Awaitables.
This function is called vf because we are returning a vector, and
we are doing a filtering operation.
$callable must return an Awaitable of bool.
The values in the Vector of the returned Awaitable are not available
until you await or join the returned Awaitable.
KeyedTraversable<Tk,T, mixed> $inputs - The KeyedTraversable of values to map.(function(T): Awaitable<bool>) $callable - The callable containing the Awaitable operation to
apply to $inputs.Awaitable<Vector<T>> - An Awaitable of Vector after the filtering operation has been
applied to the values in $inputs.<<__EntryPoint>>
async function basic_usage_main(): Awaitable<void> {
$times = ImmVector {
100000000, // Sat, 03 Mar 1973 09:46:40
200000000, // Mon, 03 May 1976 19:33:20
300000000, // Thu, 05 Jul 1979 05:20:00
400000000, // Sat, 04 Sep 1982 15:06:40
500000000, // Tue, 05 Nov 1985 00:53:20
600000000, // Thu, 05 Jan 1989 10:40:00
700000000, // Sat, 07 Mar 1992 20:26:40
800000000, // Tue, 09 May 1995 06:13:20
900000000, // Thu, 09 Jul 1998 16:00:00
1000000000, // Sun, 09 Sep 2001 01:46:40
};
// Similar to $times->filter(...)
// But awaits the awaitable result of the callback
// rather than using it directly
$saturdays =
await \HH\Asio\vf($times, async ($time) ==> (\gmdate('w', $time) === '6'));
foreach ($saturdays as $time) {
echo \gmdate('r', $time), "\n";
}
}