- array_push: documentation ( source)
- var_dump: documentation ( source)
- array_reduce: documentation ( source)
<?php
$x = array("a", "b", "c", "d", "e");
$x = array_reduce($x, function($arr, $val) {
array_push($arr, $val, $val);
return $arr;
}, []);
var_dump($x);