<?php

$array1 = array('a' => 1, 'b' => 2, 'c' => 3);
$array2 = array('d' => 4, 'e' => 5, 'f' => 6, 'a' => 'new value', '123' => 456);


var_dump(array_replace_recursive($array1, $array2));
?>