PHP sorting class

Sorting.php

<?php

/**
  * Sorting functions designed to be combined to reach desired result.
  *
  * Examples:
  * $array = array('c', 'a', 'b');
  * Sorting::sort($array, Sorting.string());
  *
  * $array = array('b' => 2, 'a' => 1);
  * Sorting::sortAssoc($array, Sorting::number());
  *
  * $array = array(array('key' => 12), array('key' => 8));
  * Sorting::sort($array, Sorting::onKey('key', Sorting::number()));
  */
class Sorting {
	public static function string() {
		return function ($a, $b) {
			return strcmp($a, $b);
		};
	}

	public static function stringNaturalOrder() {
		return function ($a, $b) {
			return strnatcmp($a, $b);
		};
	}

	public static function stringCaseInsensitive() {
		return function ($a, $b) {
			return strcasecmp($a, $b);
		};
	}

	public static function number() {
		return function ($a, $b) {
			return $a < $b ? -1 : ($a == $b ? 0 : 1);
		};
	}

	public static function reverse($comparator) {
		return function ($a, $b) use ($comparator) {
			return $comparator($b, $a);
		};
	}

	public static function onKey($key, $function) {
		return function ($a, $b) use ($key, $function) {
			return $function($a[$key], $b[$key]);
		};
	}

	public static function sort(&$array, $comparator) {
		usort($array, $comparator);
		return $array;
	}

	public static function sortAssoc(&$array, $comparator) {
		uasort($array, $comparator);
		return $array;
	}

	public static function sortOnKey(&$array, $comparator) {
		uksort($array, $comparator);
		return $array;
	}
}

// Example usage
$test = array(
	'a3' => array('kaka' => 3),
	'a1' => array('kaka' => 1),
	'a2' => array('kaka' => 2)
);

Sorting::sortAssoc($test, Sorting::onKey('kaka', Sorting::number()));

while(list($key, $value) = each($test)) {
	echo "$key: " . $value['kaka'] . "\n";
}