(PECL ds >= 1.0.0)
Ds\Sequence::apply — Updates all values by applying a callback function to each value.
    Updates all values by applying a callback function to
    each value in the sequence.
  
callback
A callable to apply to each value in the sequence.
The callback should return what the value should be replaced by.
No value is returned.
Example #1 Ds\Sequence::apply() example
<?php
$sequence = new \Ds\Sequence([1, 2, 3]);
$sequence->apply(function($value) { return $value * 2; });
print_r($sequence);
?>
The above example will output something similar to:
Ds\Vector Object
(
    [0] => 2
    [1] => 4
    [2] => 6
)