使用PHP filter_var_array（），为什么FILTER_CALLBACK将函数参数转换为字符串？

Question

In the following code, why does the callback function cast the $value argument as string?

$post_values = $_POST['dates'];
/*
var_dump of $post_values
array(1) { [0]=> array(3) { ["date"]=> string(10) "2016-05-10" ["starttime"]=> string(5) "12:30" ["endtime"]=> string(5) "14:33" } }
*/



$args = [
  'dates' => [
    'filter' => FILTER_CALLBACK,
    'options' => function ($value) {
      // The $value here has been cast to string. Why?
      // $value now has value of: string(10) "2016-05-10".
      // I expect it to be an array.
      return $value;
    }
  ]
];


$filtered_values = filter_var_array($post_values, $args);

Answer 1

This is normal behavior of filter_var() and filter_var_array() functions. Official documentation of filter_var() variable parameter contains explanation:

Note that scalar values are converted to string internally before they are filtered.