array_walk尝试写入外部数组

Question

I have a simple piece of code that isn't working as I would expect it would, could someone please explain why it isn't populating the fields array and how to solve it.

$fields = [];

array_walk($class->properties, function($v, $k) use ($fields) {
    $fields[] = $v->name;
});

die(var_dump($fields));

// output is []

Answer 1

Use this:

$fields = [];

array_walk($class->properties, function($v, $k) use (&$fields) {
    $fields[] = $v->name;
});

die(var_dump($fields));

After I wrote this I saw Mark Baker comment. That's the right answer.

For reference, see:

• http://php.net/manual/en/language.references.pass.php