array_find_key()¶
array_find_key() is a PHP native function, introduced in version 8.4 alongside array_find(), that returns the key of the first element of an array for which a callback returns a truthy value, or null if no element matches.
It is the key-returning counterpart of array_find(): where array_find() gives back the matching value, array_find_key() gives back its key, which is useful when the position, or the original index, of the match matters more than the value itself, or when that exact element needs to be updated or removed afterwards.
Because 0 and the empty string are valid, yet falsy, array keys, the result of array_find_key() must be compared against null with the identical comparison operator ===, exactly like the classic strpos() syndrome, rather than merely tested for truthiness.
<?php
$fruits = ['apple', 'banana', 'cherry'];
$key = array_find_key($fruits, fn($f) => str_starts_with($f, 'b'));
// 1
$key = array_find_key($fruits, fn($f) => str_starts_with($f, 'z'));
// null, no element matches
?>
See also PHP RFC: array_find.
Related : array_find(), Strpos() Syndrome, array_search,
Added in PHP 8.4
