HH\Lib\C\first_keyx

This API is part of the Hack Standard Library, not HHVM itself.

Returns the first key of the given KeyedTraversable, or throws if the KeyedTraversable is empty

namespace HH\Lib\C;

function first_keyx<Tk, Tv>(
    KeyedTraversable<Tk, Tv> $traversable,
): Tk;

For possibly empty Traversables, see C\first_key.

Parameters