From 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 dict where each value is the result of calling the given function on the corresponding key

namespace HH\Lib\Dict;

function from_keys<Tk as arraykey, Tv>(
  Traversable<Tk> $keys,
  (function(Tk): Tv) $value_func,
): dict<Tk, Tv>;

• To use an async function, see Dict\from_key_async().
• To create a dict from values, see Dict\from_values().
• To create a dict from key/value tuples, see Dict\from_entries().

Time complexity: O(n * f), where f is the complexity of $value_func Space complexity: O(n)

Parameters

• Traversable<Tk>$keys
• (function(Tk): Tv) $value_func

Returns

• dict<Tk, Tv>

Examples

$keys = vec[1, 2, 3, 4];
$dict = Dict\from_keys($keys, $x ==> $x + 1);
\print_r($dict);

$values = vec[1, 2, 3, 4];
$dict = Dict\from_keys($keys, $x ==> 5);
\print_r($dict);