Keys

:::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. :::

Returns a new keyset containing the keys of the given KeyedTraversable, maintaining the iteration order

namespace HH\Lib\Keyset;

function keys<Tk as arraykey, Tv>(
  KeyedTraversable<Tk, Tv> $traversable,
): keyset<Tk>;

Parameters

• KeyedTraversable<Tk,Tv> $traversable

Returns

• keyset<Tk>

Examples

$result = Keyset\keys(dict[1 => 100, 33 => 400 ]);
print_r($result);
//result: keyset[1,33]

$result = Keyset\keys(dict[]);
print_r($result);
//result: keyset[]