FromKeysOf - Hhvm — ContextQMD

:::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. :::

Creates a Set from the keys of the specified container

Hack

public static function fromKeysOf<Tk as arraykey>(
  ?KeyedContainer<Tk, mixed> $container,
): Set<Tk>;

The keys of the container will be the values of the Set.

Parameters

?KeyedContainer<Tk,mixed> $container - The container with the keys used to create the Set.

Returns

Set<Tk> - A Set built from the keys of the specified container.

Examples

This example creates new Sets from a string-keyed Map and associative array:

string-keys.hack

$fruit_calories = Map {
  'apple' => 95,
  'orange' => 45,
};

$vegetable_calories = darray[
  'cabbage' => 176,
  'potato' => 163,
];

// Create a Set from the keys of a Map
$fruit_names = Set::fromKeysOf($fruit_calories);
\var_dump($fruit_names);

// Create a Set from the keys of an associative array
$vegetable_names = Set::fromKeysOf($vegetable_calories);
\var_dump($vegetable_names);

This example creates new Sets from an int-keyed Map and associative array:

int-keys.hack

$uploaders_by_id = Map {
  4993063 => 'Amy Smith',
  9361760 => 'John Doe',
};

$commenters_by_id = darray[
  7424854 => 'Jane Roe',
  5740542 => 'Joe Bloggs',
];

// Create a Set from the integer keys of a Map
$uploader_ids = Set::fromKeysOf($uploaders_by_id);
\var_dump($uploader_ids); // $uploader_ids contains 4993063, 9361760

// Create a Set from the integer keys of an associative array
$commenter_ids = Set::fromKeysOf($commenters_by_id);
\var_dump($commenter_ids); // $commenter_ids contains 7424854, 5740542