Array Change Key Case - Hhvm

:::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 an array with all keys from input lowercased or uppercased

Hack

function array_change_key_case<Tv>(
  mixed $input,
  int $upper = CASE_LOWER,
): darray<arraykey, Tv>;

Numbered indices are left as is.

Parameters

mixed $input - The array to work on
int $upper = CASE_LOWER

Returns

mixed - - Returns an array with its keys lower or uppercased, or FALSE if input is not an array.