PHP References (&)

What Are References?

References in PHP are a way to access the same variable content by different names. They are not pointers like in C; they are symbol table aliases.

Assign by Reference

$a = 'hello';
$b = &$a;  // $b now points to the same value as $a

$b = 'world';
echo $a;  // Outputs: world

Pass by Reference

Functions can modify the original variable by accepting a reference parameter:

function addSuffix(string &$text, string $suffix): void
{
    $text .= $suffix;
}

$name = 'Stash';
addSuffix($name, 'Idea');
echo $name;  // Outputs: StashIdea

References in Loops

$items = [1, 2, 3];

foreach ($items as &$item) {
    $item *= 2;
}
unset($item);  // Important! Prevents bugs

print_r($items);  // [2, 4, 6]

Returning References

class Config
{
    private array $data = ['debug' => false];

    public function &get(string $key): mixed
    {
        return $this->data[$key];
    }
}

$config = new Config();
$debug = &$config->get('debug');
$debug = true;  // Modifies the internal array

Common Pitfalls

Dangling References

$a = 'foo';
$b = &$a;
unset($a);
echo $b;  // Still outputs: foo — only the alias is removed

Array References

$arr1 = [1, 2, 3];
$arr2 = &$arr1;
$arr2[] = 4;
// Both $arr1 and $arr2 are now [1, 2, 3, 4]