First Async

:::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. :::

:::warning Deprecated: Use C\firstx(await #A). :::

Returns the first element of the result of the given Awaitable, or null if the Traversable is empty

namespace HH\Lib\C;

function first_async<T>(
  Awaitable<Traversable<T>> $awaitable,
): Awaitable<?T>;

For non-Awaitable Traversables, see C\first.

Time complexity: O(1) Space complexity: O(1)

Parameters

• Awaitable<Traversable<T>>$awaitable

Returns

• Awaitable<?T>