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first_async

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​

Returns​