HH\Lib\C\first_key

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

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

namespace HH\Lib\C;

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

For non-empty Traversables, see C\first_keyx.

Parameters