array_merge 和 +

Be ready to surprise like this one.
array_merge renumbers numeric keys even if key is as string.
keys '1' & '2' will be updated to 0 & 1, but '1.1' & '1.2' remain the same, but they are numeric too (is_numeric('1.1') -> true)

It's better to use '+' operator or to have your own implementation for array_merge.

<?php

$x1  = array (
     '1'      =>  'Value 1' ,
     '1.1'    =>  'Value 1.1' ,
);

$x2  = array (
     '2'      =>  'Value 2' ,
     '2.1'    =>  'Value 2.1' ,
);

$x3  =  array_merge (  $x1 ,  $x2  );

echo  '<pre>NOT as expected: ' .  print_r (  $x3 ,  true  ) . '</pre>' ;

$x3  =  $x1  +  $x2 ;

echo  '<pre>As expected: ' .  print_r (  $x3 ,  true  ) . '</pre>' ;

?>

NOT as expected: Array
(
    [0] => Value 1
    [1.1] => Value 1.1
    [1] => Value 2
    [2.1] => Value 2.1
)
As expected: Array
(
    [1] => Value 1
    [1.1] => Value 1.1
    [2] => Value 2
    [2.1] => Value 2.1
)