CascadiaPHP 2024


(PHP 5 >= 5.2.0, PHP 7, PHP 8)

ArrayObject::uksortSort the entries by keys using a user-defined comparison function


public ArrayObject::uksort(callable $callback): true

This function sorts the keys of the entries using a user-supplied comparison function. The key to entry correlations will be maintained.


If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.



The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

callback(mixed $a, mixed $b): int

Returning non-integer values from the comparison function, such as float, will result in an internal cast to int of the callback's return value. So values such as 0.99 and 0.1 will both be cast to an integer value of 0, which will compare such values as equal.

Return Values

Always returns true.


Version Description
8.2.0 The return type is true now; previously, it was bool.


Example #1 ArrayObject::uksort() example

function cmp($a, $b) {
$a = preg_replace('@^(a|an|the) @', '', $a);
$b = preg_replace('@^(a|an|the) @', '', $b);
strcasecmp($a, $b);

$array = array("John" => 1, "the Earth" => 2, "an apple" => 3, "a banana" => 4);
$arrayObject = new ArrayObject($array);

foreach (
$arrayObject as $key => $value) {
"$key: $value\n";

The above example will output:

an apple: 3
a banana: 4
the Earth: 2
John: 1

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