(PECL ds >= 1.0.0)
Ds\Map::ksort — Sorts the map in-place by key
    Sorts the map in-place by key, using an optional comparator function.
  
comparatorThe 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.
  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.
 
No value is returned.
Example #1 Ds\Map::ksort() example
<?php
$map = new \Ds\Map(["b" => 2, "c" => 3, "a" => 1]);
$map->ksort();
print_r($map);
?>
The above example will output something similar to:
Ds\Map Object
(
    [0] => Ds\Pair Object
        (
            [key] => a
            [value] => 1
        )
    [1] => Ds\Pair Object
        (
            [key] => b
            [value] => 2
        )
    [2] => Ds\Pair Object
        (
            [key] => c
            [value] => 3
        )
)
Example #2 Ds\Map::ksort() example using a comparator
<?php
$map = new \Ds\Map([1 => "x", 2 => "y", 0 => "z"]);
// Reverse
$map->ksort(function($a, $b) {
    return $b <=> $a;
});
print_r($map);
?>
The above example will output something similar to:
Ds\Map Object
Ds\Map Object
(
    [0] => Ds\Pair Object
        (
            [key] => 2
            [value] => y
        )
    [1] => Ds\Pair Object
        (
            [key] => 1
            [value] => x
        )
    [2] => Ds\Pair Object
        (
            [key] => 0
            [value] => z
        )
)
