参考正在将项目添加到数组

Question

I have the following method where you pass a list of items in, and the first item is what you want to see if it exists, and the following items are the path to the item.

In the following I have 2 print_r statements, one before the for and one after it.

public function exists(){
    $keys  = func_get_args();
    $value = array_shift($keys);

    $ref = &$_SESSION;
    print_r($_SESSION);
    for($x = 0; $x < sizeof($keys); $x++){
        $ref = &$ref[$keys[$x]];
    }
    print_r($_SESSION);
    if(!is_array($ref)){
        unset($ref);
        return false;
    }
    $found = in_array($value, $ref);
    unset($ref);
    return $found;
}

and when I call it like this:

$obj->exists(123, "cart");

I get these two arrays from those print_r 's:

Array
(
    [id] => 1
    [email] => xxx@xxx.com
    [user] => TheColorRed
    [first] => Billy
    [last] => Bob
    [ZingLoggedIn] => 1
)
Array
(
    [id] => 1
    [email] => xxx@xxx.com
    [user] => TheColorRed
    [first] => Billy
    [last] => Bob
    [ZingLoggedIn] => 1
    [cart] => 
)

My question is, why is it adding cart to the array? It should only be checking to see if it exists.

Answer 1

This is the side effect of using references on array elements; if the element doesn't exist it gets created. The unset() afterwards doesn't change that. Consider not using references; since you're only reading the values, there should be no copy-on-write taking place:

public function exists()
{
    $keys  = func_get_args();
    $value = array_shift($keys);

    $ref = $_SESSION;
    foreach ($keys as $key) {
        if (!isset($ref[$key])) {
            return false;
        }
        $ref = $ref[$key];
    }
    return is_array($ref) && in_array($value, $ref);
}