Requires the Hack Standard Library to be installed.
Facebook Engineer?

This function is available as C\firstx() in Facebook's www repository.

Returns the first element of the given Traversable, or throws if the Traversable is empty

namespace HH\Lib\C;

function firstx<T>(
  Traversable<T> $traversable,
): T;
  • For possibly empty Traversables, see C\first.
  • For possibly null Traversables, see C\nfirst.
  • For single-element Traversables, see C\onlyx.
  • For Awaitables that yield Traversables, see C\firstx_async.

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



  • T