PHP Decode

--TEST--
basic array_combine test
--FILE--
<?php
    $array1 = array('green', 'red', 'yellow');
    $array2 = array('1', '2', '3');
    $array3 = array(0, 1, 2);
    $array4 = array(TRUE, FALSE, NULL);
    $a = array_combine($array1, $array1);
    $b = array_combine($array1, $array2);
    $c = array_combine($array1, $array3);
    $d = array_combine($array1, $array4);
    $e = array_combine($array2, $array1);
    $f = array_combine($array2, $array2);
    $g = array_combine($array2, $array3);
    $h = array_combine($array2, $array4);
    $i = array_combine($array3, $array1);
    $j = array_combine($array3, $array2);
    $k = array_combine($array3, $array3);
    $l = array_combine($array3, $array4);
    $m = array_combine($array4, $array1);
    $n = array_combine($array4, $array2);
    $o = array_combine($array4, $array3);
    $p = array_combine($array4, $array4);
    for($letter = "a"; $letter <= "p"; $letter++)
    {
     print_r($$letter);
    }
?>
--EXPECT--
Array
(
    [green] => green
    [red] => red
    [yellow] => yellow
)
Array
(
    [green] => 1
    [red] => 2
    [yellow] => 3
)
Array
(
    [green] => 0
    [red] => 1
    [yellow] => 2
)
Array
(
    [green] => 1
    [red] => 
    [yellow] => 
)
Array
(
    [1] => green
    [2] => red
    [3] => yellow
)
Array
(
    [1] => 1
    [2] => 2
    [3] => 3
)
Array
(
    [1] => 0
    [2] => 1
    [3] => 2
)
Array
(
    [1] => 1
    [2] => 
    [3] => 
)
Array
(
    [0] => green
    [1] => red
    [2] => yellow
)
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)
Array
(
    [0] => 0
    [1] => 1
    [2] => 2
)
Array
(
    [0] => 1
    [1] => 
    [2] => 
)
Array
(
    [1] => green
    [] => yellow
)
Array
(
    [1] => 1
    [] => 3
)
Array
(
    [1] => 0
    [] => 2
)
Array
(
    [1] => 1
    [] => 
)