Recursive function referenced collection

I'm trying to generate a collection using recursive logic by populating a referenced arra开发者_如何学Goy, but I'm not that steady on the referenced syntax. Does the below example make sense? (Have I understood how to correctly use this operator?) If not, how to accomplish this?

// I want all uniquely named subfolders returned as array
$allFolders = recursive('/');

function recursive($folder,$collection=array())
{
    /* Look up direct children here */

    foreach ($subFolders as $folder) {
         if (!isset($collection[$folder])) {
             $collection[$folder] = $folder;
             recursive($folder,&$collection);
         }
    }
    return $collection;
}

You need to declare "by reference" in the function definition - and default value is rather useless, since you won't be able to access it after the function completes. You should have it like this:

$folder = '/';
$collection = array();
recursive($folder, $collection);
print_r($collection);

function recursive($folder, &$collection)
{
    ...
}

While PHP5 will accept a default value for a by-reference argument, it makes very little sense.

You also should not use the "by reference" in the call:

recursive($folder, $collection);

While the second (by reference in the call) was allowed in earlier versions of PHP, it's been deprecated.