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from_keys

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​

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);